Дисертації: "Dosimetry gel"

1

Wong, Christopher James, and chrisjwong@yahoo com au. "High Resolution Polymer Gel Dosimetry for Small and Micro Field Dosimetry, and Development of Innovative Polymer Gel Dosimeters." RMIT University. Medical Sciences, 2009. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20091002.161512.

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Current radiotherapy techniques are focused on delivering effective treatments while sparing surrounding healthy tissues. As a result, radiotherapy treatments are using narrower and more tightly conforming therapy techniques. For these treatments to be effective an accurate measure of the dose delivered by these very narrow radiotherapy beams, both in and around the target volume, is required. It is a challenging task for the conventional type dosimeters to determine dose distribution in such small fields. The best example of such fields is microbeam beam radiotherapy (MRT), a developing treatment technique that takes this requirement even further. MRT delivers an array of micrometre size radiotherapy beams to the target. MRT has been shown to be highly effective, but reliable dosimetry of MRT is challenging due to the micrometre scales involved. Attempts to determine the MRT dose distribution have been documented for using special type dosimeters such as radioch romic film and MOSFET detectors, as well as Monte Carlo simulations. This thesis investigates polymer gels as a dosimeter for dose distribution measurements of small radiotherapy fields and microbeams. Polymer gel dosimetry is a technique which uses a tissue-equivalent gel to act as both a three-dimensional dosimeter and a phantom at the same time. These gels polymerise when exposed to ionising radiation and the response is locally dose dependent linearly. This thesis investigates the use of polymer gels for the dosimetry of small sub-centimetre (down to 3 × 3 mm2) and micrometre radiotherapy fields. A high resolution imaging technique is also required for such small beam dosimetry. This work used special high strength MRI scanners to analyse polymer gels at high resolution. This work explores the feasibility of polymer gels irradiated by microbeams and analysed using Raman spectroscopy as a dosimeter for synchrotron generated microbeams. MRT is characterised by very high doses, and special high-dose resistive types of gel were developed as part of this work. It is shown that polymer gels imagined using Raman spectroscopy techniques are capable of measuring the dose distribution of microbeam radiation techniques. This thesis also investigates the use of polymer gels to measure dose perturbations caused by metallic artefacts. Metallic artefacts, such as a surgical aneurysm clip, can be left in a patient and cause dose perturbations during radiotherapy procedures. Polymer gels were used to determine the degree of dose enhancement induced by an aneurysm clip placed inside when irradiated with a typical stereotactic radiotherapy procedure. In addition, this thesis used gels in several other innovative applications. Photonuclear interactions generated in gel by high energy x-ray beams were measured via secondary neutrons. Special clear-type gels that do not change colour with irradiation were developed. Polymer gels were investigated for dosimetry of an extremely high dose rate capacitor type linear accelerator. And polymer gels were for measurement of a high energy proton beam.

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2

Pavoni, Juliana Fernandes. "Dosimetria tridimensional por imagens de ressonância magnética com gel MAGIC modificado." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-27042010-171038/.

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Os avanços nas técnicas de tratamento com radiação ionizante estão gerando distribuições de dose muito complexas que precisam ser verificadas antes da aplicação do tratamento no paciente. Diversos dosímetros já foram propostos para esta verificação, mas o que vem apresentando os melhores resultados são os géis poliméricos que permitem a visualização tridimensional da dose. Neste trabalho desenvolvemos um gel dosimétrico do tipo MAGIC com componentes nacionais, para baratear o custo e assim, facilitar a sua aplicação na rotina clínica. Nós adicionamos formaldeído ao gel para aumentar seu ponto de fusão e facilitar seu manuseio em temperatura ambiente. A avaliação das doses foi feita através da relaxometria em imagens de ressonância magnética nuclear (IRMN). Foi encontrada uma resposta linear para dose de até 15Gy e uma dependência energética significativa para feixes de baixa energia (kVp), enquanto que para alta energia (MV) a dependência encontrada foi pequena. A variação da resposta do dosímetro em função da taxa de dose da irradiação foi menor que 5% nas taxas de 100 a 600cGy/min. A adição de formaldeído não eliminou a dependência da resposta do dosímetro para variações na temperatura durante a aquisição das IRMN, já a integridade da distribuição de dose se manteve inalterada por um período de três meses na irradiação de um campo blindado ao meio. Medidas tridimensionais de distribuição de dose foram realizadas para dois planos de radioterapia com intensidade modulada de feixe o primeiro em um acelerador linear e o segundo em um equipamento de tomoterapia, grande semelhança entre a sobreposição das isodoses e dos perfis de dose das imagens medidas com o gel e esperadas pelo sistema de planejamento (TPS) foi encontrada. A avaliação realmente tridimensional foi feita com os histogramas dose-volume (DVH), sendo que uma sobreposição entre os DVHs calculados para o volume planejado e os esperados pelo TPS foi encontrada nos dois planejamentos. Por tudo o que foi estudado, pode-se concluir que a modificação realizada no gel MAGIC resultou em um dosímetro de fácil manuseio que pode ser aplicado para medidas tridimensionais.
Advances in the treatment techniques with ionizing radiation are resulting in complex dose distributions that need to be verified before the application of the treatment in the patient. Several dosimeters have been suggested for this application, but polymeric gel dosimeters are presenting the best results so far, since they allow three dimensional dose visualization, are tissue equivalent, don\'t have dependence with angular distribution of the incident radiation and have a high spatial resolution. In this work a polymeric gel dosimeter with national components, to reduce de costs and facilitate its introduction in the clinical practice was developed. Formaldehyde was added to the gel formulation to increase its melting temperature and facilitate its use in typical room temperatures found in our country. Dose response analysis was done using nuclear magnetic resonance relaxometry. All the dosimetric characterization was done. We found a linear dose-response curve for doses until 15Gy and significant energy dependence for low energy beams (kVp), but for high energy beams (MV) this dependence is smaller. The response variation when varying the dose rate of irradiation was smaller than 5% in the dose rate range of clinical use in teletherapy (100-600cGy/min). The addition of formaldehyde did not eliminate the dosimeter dependence with variation of the scanning temperature; the integrity of dose distribution was unaltered at least for a tree month period of time in a half beam irradiation phantom. Tri-dimensional dose distributions were measured in two radiotherapy systems using intensity modulated beams, the first one in a linear accelerator and the second in a tomotherapy machine. A high similarity was found between the overlapping of isodoses and dose profiles of the dose distribution measured with the gel and expected by the treatment planning. The real tri- dimensional analysis was done with dose-volume histograms (DVH) and the DVHs measured for the planning volume and expected by the treatment planning were in good agreement. Our results show that the modification done in the gel formulation resulted in a dosimeter easy to handle and feasible for tri-dimensional measurements.

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3

Atkins, Timothy John. "Investigation of ultrasonic properties of MAGIC gels for pulse-echo gel dosimetry." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/371793/.

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This thesis describes investigations into the design and evaluation of novel ultrasonic methods for 3-dimensional ionising radiation dose verification. Pulse-echo ultrasound methods were investigated for the measurement and analysis of complex radiation therapy dose delivery. The physical properties of MAGIC (Methacrylic and Ascorbic acid in Gelatin Initiated by Copper) polymer gel dosimeters have been characterized. The variations of speed of sound, ultrasonic attenuation coefficient and density of MAGIC gel with radiation dose and temperature have been quantified. This extends work that has previously been reported for the properties of this gel to the effect of measurement temperature on the results. The facilities to perform these measurements were specified, constructed and evaluated as part of the project. The measurement of radiation dose using ultrasound back scatter from an interface between the polymer gel dosimeter and an inert reflector is demonstrated. To enable the measurement of radiation dose using pulse-echo ultrasound methods a novel inert material has been specified, manufactured and characterised. This material is matched to the acoustic impedance of MAGIC gel to produce the most dose-sensitive reflections. The reflections from the interface between the inert reflector and dose-dependent MAGIC gel have been analysed using both a single element transducer and a commercial ultrasound scanner. Both measurement systems demonstrate the same dose and temperature dependence of the ultrasonic reflection. A methodology has been developed to relate pixel values from the ultrasound scanner to the amplitude of the reflected ultrasound signal. A phantom consisting of an array of threads formed from the inert backscattering material has been designed and constructed and a method of extracting pixel data from images of the array acquired using a commercial ultrasound scanner has been developed, so that multiple imaging positions could be used to perform a 3-dimensional assessment of radiation dose distributions. It has been demonstrated that a pulse-echo technique using a commercial ultrasound scanner shows promise for radiation gel dosimetry. Further investigation and alternative polymer gel and inert reflector combinations may improve these techniques.

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4

Bäck, Sven Å J. "Implementation of MRI gel dosimetry in radiation therapy." Malmö : Lund : Malmö University Hospital ; Lund University, 1998. http://catalog.hathitrust.org/api/volumes/oclc/68945079.html.

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5

Silveira, Michely Cristina da. "Distribuição da dose absorvida no tratamento da micose fungóide através da dosimetria Fricke Xilenol Gel." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-04032011-155301/.

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A radioterapia utiliza a radiação ionizante para a destruição de células tumorais. O controle da dose absorvida de um tipo específico de radiação aplicada a um volume alvo (tumor) é feito através da dosimetria, (uso de sensores de radiação), que neste trabalho foram utilizados os dosímetros químicos Fricke e filme. Dentre os diversos tipos de câncer, indicados para tratamento, utilizando a radiação ionizante, têm-se também a neoplasia Micose Fungóide (MF), linfoma que se alastra na superfície e em profundidade na pele para o qual elétrons com alta energia são utilizados para seu tratamento, devido aos seus alcances. Neste trabalho o Fricke Xilenol Gel (FXG) foi utilizado para o planejamento do tratamento da MF, para averiguar a distribuição da dose absorvida proveniente das interações dos elétrons com os tecidos. Para tal, foram construídas cubetas especiais em acrílico (tomos) conformacionadas aos contornos do crânio e do abdômen, que uma vez preenchidas com o FXG serviram para avaliar as doses absorvidas num objeto simulador antropomórfico, o Rando Phantom. O simulador, completado com cubetas e filmes radiocrômicos, este último também conformacionado aos dois contornos de interesse, foi submetido à técnica de Stanford para irradiação do corpo total com elétrons de 6 MeV. Imagens CCD e de densidade radiográfica foram feitas e posteriormente avaliadas, através de perfis horizontais e verticais passando por seus centros. Estes a seguir foram analisados por programas computacionais: um desenvolvido no Matlab para as imagens do FXG e o outro pelo programa já conhecido, ImageJ, para as imagens do filme. Das medidas, pode-se inferir que o dosímetro FXG se presta, similarmente ao filme, para as avaliações da dose absorvida devida aos elétrons na superfície do paciente e no seu interior, devida à contaminação por raios-X.
Radioterapy uses ionizing radiation to destroy tumor cells. The absorbed dose control in a target volume is done through dosimetry, using radiation sensors, being the Fricke and film used in this study. Among several types of cancer indicated for treatment using ionizing radiation, there is also the Mycosis Fungoides (MF), lymphom that spreads on surface and depth in the skin, for which high-energy electrons are used for its treatment. In this work the Fricke Xylenol Gel (FXG) was used for MF treatment control, to obtain the absorbed dose distribution from electrons interaction with the tissues. For this scope cuvettes were manufactured of acrylic (slices), with the same contours of the skull and abdomen anthropomorphic simulator tomos. Once filled with the FXG, these cuvettes were used to infer the absorbed dose by the anthropomorphic simulator Rando Phantom. This simulator, completed with the cuvettes and radiochromic films, this last one also with the same contours similar to skull and abdomen were submitted to the Stanford technique, for 6 MeV electrons total body irradiation. CCD and radiographic density images were acquired and evaluated by horizontal and vertical profiles through theirs centers. These profiles were analyzed through a computer programs: one developed in Matlab for FXG images and the other by an already known program, ImageJ, for film images. From the results one can infer that the FXG dosimeter presents similarity with that of film, in the evaluation of the absorbed dose distribution on surface and also inside of the patient.

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6

Sakuraba, Roberto Kenji. "Desenvolvimento de um sistema de verificação dosimétrica tridimensional utilizando Solução Fricke gel na aplicação para a verificação da Radioterapia em Arco Modulado Volumétrico (VMAT) nos tratamentos com movimentação do alvo pela respiração." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/85/85131/tde-03032016-091027/.

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A Radioterapia em arco modulado volumétrico (VMAT) é uma das modalidades mais avançadas em teleterapia para o tratamento de câncer. Os diversos avanços tecnológicos, bem como a evolução das técnicas de tratamento tornaram o VMAT como uma das modalidades de estado da arte para o tratamento de alguns cânceres. Parte deste avanço é creditada à melhoria na acurácia e na prescrição de dose absorvida recomendada ao paciente ao longo dos anos. Este avanço permite que atualmente seja possível realizar os cálculos dosimétricos, por meio de sistemas de planejamento computadorizado, considerando as heterogeneidades dos pacientes, tais como: tecidos e órgãos com composições diferentes da água (meio de referência em radioterapia), contorno do paciente individualizado e o movimento dos tumores com a respiração. Tais avanços demandam o controle de qualidade destas ferramentas, com objetivo de assegurar que todo o processo de tratamento seja satisfatório e acurado. A comunidade dispõe poucos sistemas experimentais capazes de avaliar, considerando os níveis de incerteza, se os sistemas de planejamento computadorizados são aptos a considerar a movimentação dos alvos nos tratamentos com VMAT. Neste trabalho serão apresentados os resultados obtidos empregando um objeto simulador Fricke Xylenol Gel, com capacidade de mensurar as diferenças introduzidas pela movimentação, utilizando Imagem por Ressonância Magnética - MRI e comparando qualitativamente e quantitativamente os resultados. São discutidas as principais etapas de desenvolvimento deste objeto simulador, seus resultados experimentais, conclusões.
Volumetric Modulated Arc Therapy (VMAT) is one of the methods most commonly used in teletherapy to treat cancer. The various technological advances and the evolution of treatment techniques made the VMAT as one of the state of the art methods for the treatment of some cancers. Part of this improvement is credited to improvements in accuracy and prescription dose absorbed recommended to the patient over the years. This advance allows currently is possible to perform dosimetric calculations by means of the computerized planning system, considering the heterogeneity of patients, such as tissues and organs with different water compositions medium (reference radiation), and individual patient contour the movement of tumors breathing. Such advances require quality control of these tools, in order to ensure that the entire treatment process is satisfactory and accurate. Up to now, the community lacks an experimental system capable of evaluating, considering the uncertainty levels if the computerized planning systems are able to consider the movement of targets in the treatments with VMAT. In this paper, will be presented the results obtained with the phantom Fricke Xylenol Gel, capable of measuring the differences introduced by movement using the Magnetic Resonance Image - MRI and compared qualitatively and quantitatively. The main stages of the phantom development, their experimental results, conclusions and comparisons with other systems are discussed.

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7

Hurley, Christopher Anthony. "The development of normoxic polymer gel dosimetry using high resolution MRI." Queensland University of Technology, 2006. http://eprints.qut.edu.au/16442/.

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Dosimetry is a vital component of treatment planning in radiation therapy. Methods of radiation dosimetry currently include the use of: ionization chambers, thermoluminescent dosimeters (TLDs), solid-state detectors and radiographic film. However, these methods are inherently either 1D or 2D and their use involves the perturbation of the radiation beam. Although the dose distribution within tissues following radiation therapy treatments can be modeled using computerized treatment planning systems, a need exists for a dosimeter that can accurately measure dose distributions directly and produce 3D dose maps. Some radiation therapy and brachytherapy treatments require mapping the dose distributions in high-resolution (typically < 1 mm). A dosimetry technique that is capable of producing high resolution 3D dose maps of the absorbed dose distribution within tissues is required. Gel dosimetry is inherently a 3D integrating dosimeter that offers high spatial resolution, precision and accuracy. Polymer gel dosimetry is founded on the basis that monomers dissolved in the gel matrix polymerize due to the presence of free radicals produced by the radiolysis of water molecules. The amount of polymerization that occurs within a polymer gel dosimeter can be correlated to the absorbed dose. The gel matrix maintains the spatial integrity of the polymers and hence a dose distribution can be determined by imaging the irradiated polymer gel dosimeter using an imaging modality such as MRI, x-ray computed tomography (CT), ultrasound, optical CT or vibrational spectroscopy. Polymer gel dosimeters, however, suffer from oxygen contamination. Oxygen inhibits the polymerization reaction and hence polymer gel dosimeters must be manufactured, irradiated and scanned in hypoxic environments. Normoxic polymer gel dosimeters incorporate an anti-oxidant into the formulation that binds the oxygen present in the gel and allows the dosimeter to be made under normal atmospheric conditions. The first part of this study was to provide a comprehensive investigation into various formulations of polymer and normoxic polymer gel dosimeters. Several parameters were used to characterize and assess the performance of each formulation of polymer gel dosimeter including: spatial resolution and stability, temporal stability of the R2-dose response, optimal R2-dose response for changes in concentration of constituents and the effects of oxygen infiltration. This work enabled optimal formulations to be determined that would provide greater dose sensitivity. Further work was done to investigate the chemical kinetics that take place within normoxic polymer gel dosimeters from manufacture to post-irradiation. This study explored the functions that each of the constituent chemicals plays in a polymer gel dosimeter. Although normoxic polymer gel dosimeters exhibit very similar characteristics to polyacrylamide polymer gel dosimeters, one important difference between them was found to be a decrease in R2-dose sensitivity over time in the normoxic polymer gel dosimeter compared to an increase in the polyacrylamide polymer gel dosimeters. From an investigation into the function of anti-oxidants in normoxic polymer gel dosimeters, alternatives were proposed. Several alternative anti-oxidants were explored in this study that found that whilst some were reasonably effective, tetrakis (hydroxymethyl) phosphonium chloride (THPC) had the highest reaction rate. THPC was found not only to be an aggressive scavenger of oxygen, but also to increase the dose sensitivity of the gel. Hence, a formulation of normoxic polymer gel dosimeter was proposed, called MAGAT, that comprised: methacrylic acid, gelatin, hydroquinone and THPC. This formulation was examined in a similar fashion to the studies of the other formulations of polymer and normoxic polymer gel dosiemeters. The gel was found to exhibit spatial and temporal stability and an optimal formulation was proposed based on the R2-dose response. Applications such as IVBT require high-resolution dosimetry. Combined with high-resolution MRI, polymer gel dosimetry has potential as a high-resolution 3D integrated dosimeter. Thus, the second component of this study was to commission a micro-imaging MR spectrometer for use with normoxic polymer gel dosimeters and investigate artifacts related to imaging in high-resolutions. Using high-resolution MRI requires high gradient strengths that, combined with the Brownian motion of water molecules, was found to produce an attenuation of the MR signal and hence lead to a variation in the measured R2. The variation in measured R2 was found to be dependent on both the timing and amplitude of pulses in the pulse sequence used during scanning. Software was designed and coded that could accurately determine the amount of variation in measured R2 based on the pulse sequence applied to a phantom. Using this software, it is possible to correct for differences between scans using different imaging parameters or pulse sequences. A normoxic polymer gel dosimeter was irradiated using typical brachytherapy delivery and the resulting dose distributions compared with dose points predicted by the computerized treatment planning system.The R2-dose response was determined and used to convert the R2 maps of the phantoms to dose maps. The phantoms and calibration vials were imaged with an in-plane resolution of 0.1055 mm/pixel and a slice thickness of 2 mm. With such a relatively large slice thickness compared to the in-plane resolution, partial volume effects were significant, especially in the region immediately adjacent the source where high dose gradients typically exist. Estimates of the partial volume effects at various distances within the phantom were determined using a mathematical model based on dose points from the treatment planning system. The normalized and adjusted dose profiles showed very good agreement with the dose points predicted by the treatment planning system.

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8

Hepworth, Stephen J. "Investigations into polymer gel dosimetry using magnetic resonance imaging." Thesis, University of Surrey, 2000. http://epubs.surrey.ac.uk/978/.

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9

Alrushoud, Abdullah A. "Polymer gel dosimetry in radiation therapy using computed tomography." Thesis, University of Surrey, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616921.

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There have been developments in radiation therapy treatment techiques, which lead to an increase in the complexity of these treatments. The aim is to deliver highly conformal three-dimensional (3D) dose distributions, such as stereotactic radiosurgery (SRS). Polymer gel dosimetry offers three-dimensional (3D) dosimetry techniques for dose verification of dose distributions. Nisopropyl- acrylamide (NIP AM) polymer gel was the latest to develop and can be prepared under a normal atmospheric environment and has lower toxicity compared with the highly toxic polymer gels used earlier. NIPAM polymer gel using X-ray computed tomography (CT) was experimentally investigated in terms of its X-ray CT dose response, sensitivity and dose resolution. The effect of radiation beam type, radiation beam energy and radiation beam dose rate on X-ray CT dose response have also been studied. The temporal stability of NIP AM polymer gel has been examined over several days post-irradiation. The change in the polymer gel dosimeter's physical and electron densities as a function of absorbed dose was also investigated. In ,this study two new prototype phantoms were designed and constructed for imaging and irradiation of polymer gel dosimeters to provide simplicity and practicality for clinical dosimetry. The dosimetric and water equivalence properties of four NIP AM based polymer gel dosimeter formulations have been studied by examining their physical properties, interaction probability, radiation transport parameters and performing Monte Carlo modelling of depth doses. NIP AM polymer gel dosimeter irradiated at different doses using 6 Me V photon beam and 400 MU min-1 dose rate were found to have higher CT dose response (up to 37.8% at 10 Gy dose point) than results reported in the literature for NIP AM gel using similar concentration. The CT dose sensitivity of NIPAM polymer gel was found to be 0.405±0.014 H Gi1 , which is 26.2% higher than the reported sensitivity of 0.32l±0.008 H Gy-l with similar NIPAM gel concentration. The maximum change in physical density as a function of absorbed dose for polymer gel dosimeters was found to be up to ~1.0% for an absorbed dose of 20 Gy. 111

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Resende, Thiago Dias. "Um estudo para otimização da formulação do dosímetro gel MAGIC-f e avaliação da sua reutilização." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-07072017-123749/.

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A radioterapia é um procedimento que utiliza radiação ionizante de alta energia direcionado ao tumor, para destruir suas células. O objetivo é provocar o maior dano nas células tumorais enquanto se poupa o tecido sadio ao redor, para maximizar este resultado. Devido a alta complexidade dos feixes usados nestes tratamentos, um dosímetro tridimensional é desejado para garantir que a dose esteja sendo entregue da forma como foi planejada, sendo a dosimetria gel polimérica com leitura da dose em Imagens de Ressonância Magnética Nuclear (IRMN), uma opção para esta medida. Esse trabalho utiliza o dosímetro gel polimérico MAGIC-f como referência e tem como objetivo otimizar sua formulação, substituindo inicialmente os seus agentes antioxidantes (sulfato de cobre e ácido ascórbico) por um antioxidante mais potente, o cloreto de tetrakishidroximetilfosfônio (THPC), e, em seguida, variar as concentrações dos demais componentes do dosímetro a fim de obter a menor concentração de cada um deles que resulte em um dosímetro com sensibilidade adequada para uso em radioterapia.Foram feitas análises sobre a estabilidade térmica do dosímetro com THPC e estudos sobre as concentrações ideais de THPC (2mM, 5mM, 8mM, 10mM ou 20mM); Ácido Metacrílico (2%, 2,5%, 3%, 3,5% ou 4%); Gelatina (4%, 6%, 8% ou 10%). Após todas as modificações, a formulação otimizada contendo 88,96% Água MiliQ; 3% Ácido Metacrílico; 8% Gelatina; 0,04% THPC (5mM de concentração), apresentou uma sensibilidade próxima a 1,03 Gy-1s-1 e um ponto de fusão de aproximadamente 50C, utilizando as menores quantidades possíveis dos reagentes químicos e a sequência de leitura das IRMN implementada para esta dosimetria. O dosímetro otimizado obtido teve uma redução de 40% no seu custo, em comparação com o dosímetro MAGIC-f, e uma resolução de dose de 0,18 Gy. Obteve linearidade de resposta a dosede 0 a 10 Gy. Uma variação máxima na sensibilidade do dosímetro de 8,5% foi encontrada ao se variar a taxa de dose de 300 500 cGy/min.Também foi avaliada a integridade da distribuição de dose para esse dosímetro através da avaliação de uma irradiação com meio campo blindado. E, sua a maior variação em um teste de repetitividade foi de 15%. Um outro objetivo deste trabalho foi o desenvolvimento de uma metodologia para a reutilização do dosímetro gel, sendo que um dosímetro previamente irradiado com uma dose de 2Gy foi reutilizado após seu derretimento a 50C em um forno com controle digital de temperatura, seguido por uma nova gelificação.Para garantir sua resposta, foi necessária a readição de agentes antioxidantes à formulação reutilizada. Dessa forma, para o gel MAGAT com 1mM de THPC foi obtida uma sensibilidade 30% menor que a original para o dosímetro reutilizado e 15% para o mesmo dosímetro, com 2mM de THPC
Radiotherapy is a procedure that uses high energy ionizing radiation directed to the tumor to destroy its cells. The objective is to obtain tumoral cells more damaged avoiding the healthy cells around it and increase this result. Due to the high complexity of the energy beams used on these treatments, a three-dimensional dosimeter is demanded to assure that the dose is focused as planned, being the polymeric gel dosimetry using Nuclear Magnetic Resonance Images (NMRI) for dose scanning an option to this measurement. This work uses MAGIC-f gel as reference and its objective is to optimize the dosimeter formulation, by initiallyreplacing the antioxidants agents (Copper Sulfate and Ascorbic Acid) by a more power rating antioxidant, Tetrakis (hydroxymethyl) phosphonium chloride (THPC), and then, variatingthe others dosimeter´s components concentration in order to obtain the smallest concentration of each one that result in an adequate dosimeter´ssensitivity for radiotherapy application. Studies were made to check the thermal stability of the gel containing THPC and studies were carried out about the ideals concentrations of THPC (2mM, 5mM, 8mM, 10mM or 20mM); Methacrylic Acid (2%, 2.5%, 3%, 3.5% or 4%); Gelatin (4%, 6%, 8% or 10%). After the modifications, the optimized formulation containing 88.96% of mili-Q water; 3% of methacrylic acid; 8% of gelatine; 0.04% of THPC (5mM) showed a sensitivity of approximately 1.03 Gy-1s-1 and a melting point approximately of 50°C, using the smallest possible chemical compounds concentrations and the NMRI scanning sequence implemented for this dosimetry. The optimized dosimeter obtained presents a 40% cost reduction, comparing with the dosimeter MAGIC-f, and a dose resolution of 0.18 Gy. The dosimeter responds linearlywith doses from 0 to 10 Gy. A maximal sensitivity variation of 8.5% was found when varing the dose rate from 300 to 500 cGy/min. Its dose integrity was checked by a half beam blocked irradiation. And its largestsensitivity variation at a repeatability test was 15%. The second objective of this work was the development of a methodology for reusing the dosimeter.The dosimeter previously irradiated with 2Gy was reused after being melted in a digitaltemperature control oven at 50°C, followed by the re-addition of THPC and a new gelation. The reused MAGAT gel dosimeter with 1mM of THPC presented 30% sensitivity reductioin when compared to the the same dosimeter before the reusing process, while the MAGAT gel with 2mMof THPC presented a reduction of only 15%

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Neto, Euclydes Borguezan. "Gel Turnbull Blue aplicado à dosimetria de radiação ultravioleta e visível." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-22122016-135858/.

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O gel radiocrômico Turnbull Blue (TBG) é sensível a raios gamma e x. Este composto tem sido utilizado em dosimetria de radiações ionizantes devido à sua capacidade de simular tecido biológico quando exposto à radiação de alta energia. Após sua irradiação, o TBG sofre uma mudança de cor: o aspecto amarelo torna-se azul devido à formação do corante Turnbull Blue. Essa alteração de cor produz uma larga banda de absorção na faixa espectral do visível, com pico localizado em 690 nm. A intensidade desta banda é proporcional à dose de radiação absorvida. Entretanto, o comportamento do TBG, quando exposto a radiações menos energéticas, como luz visível e ultravioleta, ainda não é conhecido. Considerando as recomendações de organizações internacionais sobre os riscos do uso de tais radiações, esta pesquisa teve como objetivo caracterizar a resposta do TBG, quando irradiado por diferentes fontes ultravioletas e visíveis, tais como lâmpadas fluorescentes, LEDs e um simulador solar. O tempo entre a exposição do gel e a leitura de sua resposta foi estudado, assim como a influência da utilização de fontes com diferentes irradiâncias e diferentes temperaturas de irradiação. Um espectrômetro, operando na faixa espectral de 350 nm a 900 nm, foi utilizado para mensurar a mudança de cor no gel. Os resultados mostraram que o gel possui diferentes sensibilidades de acordo com a faixa espectral entregue pela fonte: a radiação UVC produziu a alteração de cor mais intensa, seguida pela UVB, UVA e visível, respectivamente. A temperatura de irradiação e a irradiância da fonte tiveram influência considerável na mudança de cor do TBG. Os resultados mostraram que é possível usar o gel TBG como um dosímetro de radiação óptica, desde que fatores de correção relacionados à irradiância da fonte e temperatura de irradiação sejam levados em consideração.
The radiochromic gel Turnbull Blue (TBG) is sensitive to gamma and x-rays. This compound has been utilized in ionizing radiation dosimetry, since it acts as biological tissue simulator when exposed to high-energy radiation. Subsequently to its radiation, TBG shows a color shift: the original yellow aspect becomes blue due to the production of the colorant Turnbull Blue. Such chromic shift yields a broad absorption band in the visible spectral range, with a peak located at 690 nm. The intensity of this band is proportional to the absorbed radiation dose. However, the behavior of TBG when exposed to less energetic radiation, e.g. ultraviolet and visible light, remains unclear. Considering the recommendations of international organizations regarding the risks of using such type of radiation, this research aimed to characterize the TBG response when irradiated by different ultraviolet and visible sources as well as to determine its sensitivity to the radiation in the UV-Visible spectral range. Furthermore, this investigation evaluated the viability of TBG as an optical dosimeter. During this study, the gel was exposed to different non-ionizing radiation sources, such as fluorescent lamps, LEDs and a sun simulator. The time between the gel exposition and the measurement of its response was studied, as well as the influence of different source irradiances and temperatures of irradiation. A spectrometer operating on the 350-900 nm spectral range has measured the gel color shift. The results showed different sensitivities according to the spectral range delivered by the source: UVC has produced the most intense change in color, followed by UVB, UVA and visible, respectively. The temperature of irradiation and the irradiance provided by the sources have shown considerable influence on the color shift. The results showed that it is possible to use the TBG gel as optical radiation dosimeter. The use of correction factors for temperature of irradiation and irradiance of the source are mandatory.

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12

Farajollahi, Ali Reza. "An investigation into the applications of polymer gel dosimetry in radiotherapy." Thesis, Online version, 1998. http://ethos.bl.uk/OrderDetails.do?did=1&uin=uk.bl.ethos.284699.

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13

Pastorello, Bruno Fraccini. "Montagem e caracterização de um fantoma para utilização em radioterapia utilizando imagens convencionais por ressonância magnética e contraste por transferência de magnetização." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-11092007-160124/.

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A dosimetria 3D utilizando gel à base de monômeros é uma importante ferramenta utilizada em casos de Radioterapia, em que há necessidade de uma alta resolução da distribuição espacial de dose. Neste trabalho, desenvolvemos um gel à base de monômeros do acido metacrilico, denominado MAGIC®, com a finalidade de avaliar a distribuição espacial de dose em simulações de tratamento de radioterapia, utilizando duas técnicas de imagens por ressonância magnética, Magnetic Resonance Imaging (MRI): a relaxometria (RT) e a transferência de magnetização (Magnetization Transfer, MT). Para tal, o trabalho foi desenvolvido em três etapas. Na primeira, desenvolvemos fantomas para serem irradiados com radiação ? e x, sobre os quais imagens de ressonância foram obtidas e analisadas. Desenvolvemos também um software, escrito em Matlab®, para analisar as imagens e traçar curvas de isodose dos fantomas irradiados. Em seguida, aperfeiçoamos o preparo, a composição, e as maneiras de adquirir e processar as imagens do gel irradiado. Nessa etapa incorporamos o formaldeido ao gel MAGIC, aumentando sua sensibilidade em 15%. Por fim, simulamos cinco configurações de tratamento de radioterapia e avaliamos as isodoses adquiridas, comparando-as com aquelas obtidas pelo software de planejamento radioterápico virtual, TPS®. As avaliações feitas com a técnica de relaxometria corresponderam às nossas expectativas. Com ela foi possível caracterizar o gel MAGIC, com alguns testes dosimétricos, bem como avaliar as 5 simulações de tratamentos radioterápicos propostas. O gel se mostrou linear até 20 Gy, mas não apresentou níveis aceitáveis de reprodutibilidade, necessitando de uma curva de calibração em cada teste. O gel possui número atômico efetivo próximo ao da água não necessitando de fatores de correções. Na maioria dos casos simulados, as isodoses das simulações feitas com o gel MAGIC reproduziram as simulações virtuais. Infelizmente, não obtivemos, por enquanto, o mesmo sucesso com a avaliação por MT. As imagens de MT não se mostraram confiáveis e por esse motivo as simulações com o gel só foram feitas com a técnica de RT.
The 3D monomeric gel dosimetry is an important tool in radiation therapy cases which needs high spatial dose resolution. In this work we developed a methacrilic acid monomeric gel called MAGIC® to evaluate spatial dose distributions in simulations of radiation therapy treatments. We used two Magnetic Resonance Imaging (MRI) techniques, the relaxometry (RT) and the magnetization transfer (MT). The work was developed in three stages. First of all, the phantoms were created to be irradiated using and x radiations, the MRI were acquired and analyzed. We also developed a software, programmed in Matlab®, to analyze the images and to draw isodoses curves of irradiated phantoms. Following it, we improved the way the gel was prepared and its composition, as well the image acquisition and processing. In this part we added formaldehyde to the gel, improving its sensibility in 15%. Finally, we simulated 5 different radiation therapy treatments and compared the isodoses measured with the isodoses of the radiation therapy treatment planning software (TPS®). The results of the RT technique corresponded to our expectations. Using the RT we characterized the gel with dosimetric tests and evaluated five different radiation therapy treatments. The gel showed a linear relation with the dose until 20 Gy, but the results of the tests were not reproducibles, because of that we made a calibration curve for each test. The effective atomic number of the gel is close to the water, so it was not necessary any correction. In most of the simulated cases, the isodoses measured with the gel reproduced the virtual simulations. Unfortunately, until now, we didn\' t have the same success using the MT technique. The MT images were not reliable and because of that the simulations were only made with the RT technique.

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14

Zaias, Herofen. "Desenvolvimento de um novo gel e otimização de leitor para dosimetria química." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-30092010-110923/.

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O interesse científico em se conhecer os efeitos provocados pelo uso da radiação ionizante nos sistemas biológicos, fez com que a área da dosimetria merecesse uma atenção especial na busca de sensores que pudessem traduzir respostas equivalentes às dos tecidos humanos. O presente trabalho mostra a caracterização preliminar e a aplicação de um novo dosímetro químico (FXGA), derivado do FXG, que se diferencia do anterior pela substituição da gelatina de pele de porco \"300 Bloom\" por uma nacional. As leituras de dose absorvida por esse dosímetro são baseadas na absorção ótica e para tal foi desenvolvido um protótipo portátil (RADIARE III), que se mostrou prático e acessível economicamente em relação a um espectrofotômetro. A partir das medidas realizadas pode-se inferir que o dosímetro FXGA possui comportamento linear com a dose absorvida no intervalo de 0,5 à 35 Gy para fótons do 60Co, e de 1 à 7 Gy para elétrons com energias de 5, 8 e 10 MeV. Também a dependência energética para fótons e elétrons foram obtidas e seus comportamentos são coerentes com o esperado. Aplicações na radioterapia foram obtidas, como: perfil, fator de campo e percentual de dose profunda para fótons do 60Co. Dos resultados obtidos da caracterização para fótons e elétrons, bem como dos parâmetros físicos para o equipamento 60Co, o sistema dosimétrico \"gel FXGA + protótipo RADIARE III\" mostrou-se promissor para ser utilizado no controle de qualidade de um serviço de radioterapia.
Researchs with radiation dosimeters look for materials that presents similar response to radiation as biological systems. This work presents preliminar characterization and radiotherapy application from a new chemical dosimeter (FXGA), derived from the FXG with a difference due to the gelatin used (pork skin \"300 Bloom\" for FXG and national gelatin for FXGA). The FXGA absorbed dose reading are based on the optic absorption, and for this reason a reader (RADIARE III) was developed, which is portable and economically accessible when compared with an spectrophotometer. From the measurements done, it can be inferred that FXGA dosimeter possess linear response with the absorbed dose from 0.5 up to 35 Gy for 60Co photons and from up 1 up to 7 Gy for 5, 8 and 10 MeV. The energy dependence for photons and electrons were obtained and their response are coherent those expected. FXGA radiotherapy applications had been done as field factor, profile and percentage depth dose for 60Co photons. From the characterization results for photons and electrons, as well from physical parameters for the 60Co , one can figure out that the dosimetric system \"FXGA gel + RADIARE III reader\" can be an attractive tool for the quality control in a radiotherapy service.

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Mangueira, Thyago Fressatti. "Avaliação dosimétrica da solução fricke gel usando a técnica de espectrofotometria para aplicação na dosimetria de elétrons e nêutrons." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/85/85131/tde-29032012-144938/.

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Neste trabalho as principais características dosímetricas da solução Fricke Xilenol Gel (FXG) foram estabelecidas para futura aplicação clínica na dosimetria de elétrons. As curvas de dose resposta para feixes de nêutrons térmicos para pesquisa em Terapia por Captura de Nêutrons (BNCT) e feixes elétrons de aplicação industrial também foram determinadas. A técnica padrão de leitura utilizada foi espectrofotometria. Para o feixe clínico as reprodutibilidades intra e inter-lotes da solução FXG são melhores que 1,4 % e 5,1 % respectivamente, o comportamento da resposta para o intervalo de dose entre 0,2 e 40 Gy é linear e independente da energia e da taxa de dose para o intervalo estudado. Devido aos efeitos da oxidação natural do FXG o tempo ótimo entre o preparo e a irradiação é de 24h e o comportamento da curva de dose resposta não se altera no período estudado para a variação da absorvância líquida do dosímetro. Para o estudo com o campo de nêutrons as curvas de dose resposta do FXG apresentaram comportamento linear em todo intervalo de dose estudado, e para campos industriais de elétrons o comportamento é exponencial decrescente. De acordo com os resultados obtidos para os feixes de radiação estudados, não houve alteração na posição das bandas características do espectro de absorção do FXG. Como testes adicionais, foi determinada a viabilidade do uso do método de leitura do FXG por imagens fotográficas digitais e aplicação do FXG na dosimetria para braquiterapia intracavitária. O bom desempenho do dosímetro FXG nos testes realizados indica que este pode ser utilizado na avaliação tridimensional da dose em tratamento radioterápicos.
In this work the main dosimetric characteristics of the Fricke Xylenol Gel (FXG) solution were established for further application in the measurement of dose distribution of clinical electron fields. The dose-response curves of the FXG in a neutron field were also evaluated for the research in Boron Neutron Capture Therapy (BNCT) and industrial electron fields. The standard reading technique was the spectrophotometric. For the clinical field, the intra and inter-batch reproducibility are better than 1.4% and 5.1 %, respectively, the response presents a linear behavior for doses ranging from 0.2 to 40 Gy independently of the energy and the dose rate in the studied ranges. Due to the effects of the FXG natural oxidation, the optimum elapsed time between FXG preparation and irradiation was established as 24h period and the behavior of the dose-response curve of the FXG using the variation in the absorbance relative to the non-irradiated dosimeter as a basis during the whole studied period were not altered. The dose-response to the industrial electron beam presented an exponential decreasing behavior and the neutron beam for research in BNCT presented a linear behavior for the complete studied dose range. According to the obtained results for the different types of radiation studied for the FXG, there was no change in the position of the characteristic bands of the absorption spectrum due to the interaction of these radiation types. Additional tests were performed to determine the digital photographic imaging of FXG analyses viability and the application of FXG dosimetry on intracavitary brachytherapy. The good performance of the FXG dosimeter in the tests that were carried out indicates that this dosimeter may be applied to the tri-dimensional dose evaluation in radiotherapic treatments using electrons and neutron beams.

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Camargo, Shiva do Valle. "Confecção e caracterização de dosímetros luminescentes de cerâmicas de BaTiO3 nanoestruturadas." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/3/3140/tde-11072014-093623/.

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Conforme pesquisas realizadas na literatura, o estudo do Titanato de Bário (BTO) na dosimetria é inédito, este material foi escolhido porque exibe propriedades luminescentes, demonstradas em experimentos de medidas de espectros de emissão. Para a confecção do BTO fez-se o uso da técnica química Sol-Gel, foi produzido amostras de BTO Puro, BTO dopado e co-dopado com diversas terras-raras. Todas as amostras produzidas sofreram calcinações com temperaturas definidas em 800, 1000 e 1200°C. As dopagens foram realizadas com os seguintes elementos terras-raras: Nd, Tb, Eu, Yb, Er, Pr, e as amostras co-dopadas foram com Tb/Eu e Yb/Er; no total foram confeccionadas trinta e uma amostras. No estudo de redução de massa foi constatada uma redução de metade das massas das amostras durante o processo de calcinação. Nas análises de Termoluminescência (TL) pelo menos uns dos tipos de calcinações apresentaram picos TL, com exceção das amostras co-dopadas com Tb/Eu. As amostras dopadas com Eu e Tb se destacaram nas análises das respostas termoluminescentes. A amostra com Tb e calcinada a 1200°C forneceu pico TL entre 90 a 200°C, e a dopada com Eu (1mol%) e calcinado a 1000°C apresentou picos TL em 110°C e 370°C. A mínima dose detectável para o pico de 110°C foi de 119 mGy e para o pico de 370°C foi de 143 mGy. As análises de MEV mostraram que as micrografias das amostras de BTO dopado tanto com Tb, quanto com Eu apresentaram superfícies porosas, diferentemente das Puras, que apresentaram superfície mais lisa. As análises de DRX indicaram uma fase tetragonal para as amostras Pura e dopadas com Eu (1 mol%), ambas calcinadas a 1000°C.
According to the literature, the study of Barium Titanate (BTO) for dosimetry is unpublished yet, this material was chosen because it exhibits luminescent properties, demonstrated in emission spectra experiments. To make the BTO samples the chemical sol-gel technique was used. Samples of BTO Pure, doped and co-doped with different rare earths were made. All produced samples were calcinated with temperatures at 800, 1000 and 1200°C. The doping was performed with the following rare earths: Nd, Tb, Eu, Yb, Er, Pr, and some samples were co-doped with Tb / Eu and Yb / Er; in total were made thirty-one samples. In the study of weight reduction, a reduction, by half of the mass of raw material, was observed during the calcination process. In the TL analysis, at least one of the types (temperature) of calcinations provides TL peaks formation, except for the samples co-doped with Tb / Eu. The BTO: Eu and Tb provided the best TL response. The BTO: Tb and calcined at 1200°C showed TL peak at 90 to 200°C and the one doped with Eu (1mol%) and calcined at 1000°C supplied peaks at 110°C and 370°C. The minimum detectable dose to the TL peak at 110°C was 119 mGy and for TL peak at 370°C was 143 mGy. SEM analyzes showed that the micrographs of BTO samples doped with both Tb and Eu supplied porous surfaces, unlike the pure sample, that showed smoother surface. XRD analyzes indicated a tetragonal phase to pure sample and the one doped with Eu (1 mol%), both calcined at 1000°C.

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Courter, Erik Joseph-Leonard. "Use of ClearView Gel Dosimeter for Quality Assurance and Testing of Stereotactic Radiosurgery." Wright State University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=wright1466417256.

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Oliveira, David Marçal Machado de. "Verificação do uso do dosímetro Fricke benzóico xilenol gel em tomografia computadorizada." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-08122011-154718/.

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A tomografia computadorizada (CT) representa a maior fonte de exposição aos raios X médicos e seu uso continua crescendo rapidamente, devido aos aparelhos de última geração com alta resolução de contraste. Uma avaliação dos parâmetros que influenciam a dose absorvida na tomografia asseguram o controle de qualidade e aceitação do equipamento. Os protocolos de CT utilizam câmara de ionização e filme radiográfico para esta avaliação e pela primeira vez, neste trabalho, o dosímetro químico Fricke Benzóico Xilenol Gel (FBXG) foi utilizado. Este dosímetro ao ser irradiado, produz um complexo colorido (Fe^{+3}-AX) possível de ser medido através de técnicas ópticas, acústicas e de ressonância magnética. A leitura do filme e FBXG por fotografia, também foi empregada pela primeira vez neste trabalho indicando ser adequada. Da utilização do FBXG para avaliação do CT, foi possível obter os parâmetros de espessura de corte, homogeneidade de campo e curvas de isodose, além da promissora indicação dos índices de dose em tomografia.
Computed tomography now represents the single largest source of medical exposure and its use is increasing rapidly, because of new generation units and hight contrast image. The acceptance and quality control tests of this equipment can be inferred through some parameters that influence the absorbed dose, such as axial and transaxial dose profile and CT dose indexes. Although ionization chamber and radiographic films are indicated by protocols for these evaluations, in this present work, beside this two dosimeters, we use the chemical dosimeter Fricke Benzoic Xylenol Gel (FBXG). This dosimeter when irradiated produces a colored complex (Fe^{+3}-XO), that in this work was measured photographically to obtain the parameters, once this technique as well the FBXG are linearly dependent on the absorbed dose. This reading technique was adequate to obtain the calibration curve, the axial and transaxial dose profile for the FBXG, besides to let us visualize the future acquiring of tomographic dose indexes.

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Amin, Md Nurul. "Polymer gel dosimetry applied to β particles, electrons and 300 kV X-rays". Thesis, University of Leicester, 2003. http://hdl.handle.net/2381/29451.

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Polymer gels were used with magnetic resonance imaging (MRI) to measure three-dimensional absorbed dose distributions for beta particles, electron and x-rays beams that are used in radiotherapy. The manufacturing processes and calibration procedures for two dosimeters (hypoxic PAG and normoxic MAGIC gels) were investigated. The response of both gels was energy independent over a range of electron and photon energies commonly used for radiotherapy. However, dose response of both gels was dependent on the temperature at the time of MR scanning, while MAGIC was also dependent on the temperature at the time of irradiation, which had not been previously reported. Results suggest that MAGIC gel is superior to PAG, since it is easier to manufacture and unaffected by oxygen diffusion through wall materials. The potential usefulness of both types of gel in different areas of radiotherapy was studied, including vascular brachytherapy. Results were compared with doses measured using radio- chromic film, confirming that dose distributions for vascular brachytherapy sources with a high dose gradient can be measured using PAG. However, because of the disadvantages of the gel manufacturing process and the need for access to a high-resolution scanner, it was concluded that radio-chromic film would be the method of choice for routine quality assurance in brachytherapy. PAG and MAGIC gels were also used for dosimetry across the junction of 6MV photon and 12MeV electron fields that are often used in radiotherapy. Different photon field configurations were studied, and dose profiles were measured. For each configuration either significant "hot" or "cold spots" were measured, with good agreement between the MAGIC and PAG and radio- chromic film. This work has confirmed the usefulness of gel dosimetry in radiotherapy in general, and in beta and electron dosimetry in particular. In addition, these studies have quantified the advantages of normoxic gels over the hypoxic PAG.

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Pires, Elcio Liberato. "Síntese e caracterização de elemento sensor de matriz KAISi3O8, dopadas com Mn ou Gd, obtidos pela técnica sol-gel, visando a aplicação em dosimetria das radiações ionizantes por termoluminescência e luminescência opticamente estimulada." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/3/3140/tde-19012011-104913/.

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Neste trabalho, estudou-se as propriedades termoluminescentes e fotoluminescentes (em processo anti-Stokes), além de algumas propriedades químicas e físicas, de amostras sintéticas de KAlSi3O8, dopadas com Mn ou Gd, obtidas por meio da técnica sol-gel. O objetivo principal do estudo foi a obtenção de um novo material, com possibilidades reais de aplicação em dosimetria das radiações ionizantes, como elemento sensor de dosímetros luminescentes. As amostras foram obtidas e trabalhadas na forma de pós com tamanho médio de partícula em 600 nm e suas estruturas composta por uma matriz amorfa e com presença de nano partículas, presente apenas nas amostras dopadas. Os resultados de EPR mostraram que os dopantes incorporaram na matriz sob a valência de Mn2+ e Gd3+ respectivamente. As curvas de emissão TL apresentaram formatos semelhantes para todas as regiões estudadas, com a presença de um pico principal de intensidade alta e reprodutível em torno de 170°C. As curvas de decaimento da LOE da amostra não dopada e dopada com Mn exibiram um decaimento total da luminescência para 40 s de estimulação centrada em 470 nm; por outro lado, a amostra dopada com Gd, exibiu um rápido decaimento da LOE (aproximadamente 71,4 % da intensidade inicial), para os primeiros 40 s de estimulação, seguida por um decaimento mais lento e persistente para o restante do período de estimulação, o que indica claramente a presença de duas componentes de decaimento. As amostras dopadas com Mn apresentaram emissão TL mais intensa em torno 570 nm, sendo mais eficientes para os estudos de TL no VIS; enquanto que, as dopadas com Gd, exibiram emissão mais intensa em 470 nm, porém, devido ao formato dos sinais (presença de um único pico aparente), mostraram-se melhor para os estudos de LOE e TL no UV. As amostras dopadas com 0,5% e 8% em mol de Mn e Gd, respectivamente, apresentaram os sinais luminescentes mais intensos, tanto para LOE quanto para TL. No estudo da dependência energética para diferentes energias de raios-X, o tipo de dopante influenciou no padrão de resposta obtido, tendo sido observado um decréscimo da intensidade luminescente com o aumento da energia para a amostra dopada com Mn; para a amostra não dopada e dopada com Gd, não se observou um padrão de decréscimo ou aumento da intensidade com a energia. As curvas de calibração foram ajustadas por meio de retas com grau de confiabilidade alto (fator R2 próximo a 1), e as menores doses detectáveis variaram entre 20 e 60 mGy aproximadamente. Todas as amostras apresentaram perdas consideráveis de intensidade luminescente com o passar do tempo após irradiação, e que foi de aproximadamente 80%, em média, para os 10 primeiros dias. Concluiu-se que, a princípio, os materiais têm maior possibilidade de aplicação na dosimetria em tempo real do que na dosimetria convencional ou passiva por TLDs, devido a sua alta resposta luminescente. Contudo, estudos futuros a respeito de tratamento térmico prévio, podem viabilizá-los a esta última aplicação. Com relação ao campo de aplicação, sugere-se a dosimetria ambiental, devido aos valores Z obtidos, que estão mais próximos do dos materiais que compões rochas e sedimentos.
In this work the thermoluminescent and photoluminescent properties (in the anti-Stokes process), and some other chemical and physical properties of KAlSi3O8 synthetic samples, doped with Mn or Gd, obtained by sol-gel method, were studied. The main goal of this study was to obtain a new material, with real possibility of application in ionizing radiation dosimetry as sensor element in luminescent dosimeters. The obtained samples were composed of powders with average particle size around 600 nm and they structures were composed of an amorphous matrix with presence of nanoparticles, observed only in the doped samples. The EPR results showed that the dopants incorporated in the matrix in the Mn2+ and Gd3+ valences, respectively. The TL glow curves exhibited a similar pattern for all the studied regions, composed of a main high-intensity and reproducible peak around 170 °C. The OSL shine-down curves for the undoped and Mn doped samples exhibited a total decay of luminescence for 40 s of stimulation centered at 470 nm; on the other hand, Gd doped sample exhibited an quick OSL decay (approximately 71.4 % of the initial intensity), for the first 40 s of stimulation, followed by a slower and more persistent decay, which clearly indicates the presence of two decay components. Mn doped samples showed the highest TL emission around 570 nm, being more efficient for the TL studies in the VIS, while the Gd doped samples exhibited the highest emission at 470 nm; however, due to the obtained curve pattern (with an apparent single peak), they had shown more efficient results for the applications in the UV. The samples doped with 0.5 and 8 mol% of Mn and Gd, respectively, showed the highest luminescent response improvement for OSL and TL. Energetic dependence on different X-rays energies study showed that the dopants changed the obtained response pattern. The Mn doped sample exhibited a decrease in luminescent response, while the Gd and the undoped samples do not show a pattern of decrease or increase in luminescence. The calibration curves were fitted by straight lines with high reliability degree (R2 near to 1), and the lowest detectable doses were between 20 and 60 mGy. All the samples exhibited considerable losses in luminescent intensity with the time after irradiation (about 80% for the firsts 10 days). From the results it was concluded that the studied materials are more applicable to real time than to passive TLD dosimetry, due to their high luminescent response. However, studies about previous heating treatment could make them feasible for the last application. The use of these materials in environmental dosimetry is suggested due to the obtained Z values, which are closer to those which form rocks and sediments.

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Rojas, Diana Maritza Cuevas. "Dosimetria 3D de um tratamento simulado de próstata na presença de próteses femorais metálicas." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-11072017-094424/.

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Historicamente a radioterapia é divida em radioterapia externa, braquiterapia e radioisotopoterapia sistemática. As diferenças entre as três está no posicionamento da fonte de radiação com respeito ao corpo humano. Na radioterapia externa a fonte fica a uma certa distância do paciente, já no caso da braquiterapia as fontes podem ser inseridas dentro de cavidades do corpo ou implantadas diretamente nos tecidos. Na radioisotopoterapia sistemática isótopos radiativos são administrados por via oral ou venosa. Dessas três a radioterapia externa é a mais usada pois, ela permite realizar planejamentos de radioterapia em três dimensões (3D), partindo inicialmente de uma tomografia computadorizada da região do tumor. O planejamento baseado na tomografia computadorizada permite que a distribuição da radiação nos tecidos seja feito com mais precisão evitando assim, que os tecidos sadios sejam afetados. Nesse trabalho a radioterapia externa convencional, foi implementada e executada para um tratamento de próstata com implantes metálicos, usando 4 campos de irradiação (0, 90, 180, 270 graus) e uma dose total planejada de 70 Gy fracionada em 35 sessões, cada uma com 2 Gy. Em qualquer tipo de tratamento que envolva a radiação ionizante é exigido um controle de qualidade para assim, determinar se a dose inicialmente planejada será entregue ou não ao tumor. Idealmente deveria ser implementado um controle de qualidade em três dimensões mas, até o momento não há um dosímetro 3D consolidado na rotina clinica. No entanto, o uso de géis poliméricos associados à técnica de leitura de dose com imagem de ressonância magnética (IRM) possibilita a dosimetria tridimensional. Nesse contexto, é aplicada a dosimetria 3D usando para isso, o gel magic com formaldeído (magic-f). Além da dosimetria 3D, foram realizadas medidas de dose absorvida por meio de dosimetria pontual, para tal fim são utilizados dosímetros termoluminescentes e de alanina. Na avaliação da distribuição de dose feita pelo planejamento e a medida com o gel é usado a análise gama (3%/3mm), neste caso, a distribuição de dose medida concorda com a distribuição de dose planejada TPS. A análise gama apresenta um porcentagem de aprovação do 93%. Os valores de dose absorvida na interface osso-metal determinados pelos dosímetros TL apresentam um aumento de 1,73 Gy na região do osso sacro e outros aumentos entre o 0,16 e 0,33 Gy foram encontrados em regiões como a cabeça do fêmur e quadril. Esses aumentos na dose foram só para duas sessões com doses entregadas ao fantom de 2 Gy. De igual maneira para os dosímetros de alanina se encontro um aumento na dose de 1,22 e 2,42 Gy na região do osso sacro. O planejamento feito nesse caso foi de 6 Gy. Os resultados evidentemente mostram como as inomogeneidades de um material com número atómico alto, gera perturbações sobre as distribuições de dose inicialmente planejadas.
Historically, Radiotherapy is divided into external radiotherapy, brachytherapy and systemic radioisotopotherapy. The difference between the three lies in the position of the radiation source regarding the human body. In external radiotherapy the source is at a certain distances of patient, and in the case of brachytherapy, this source can be inserted into cavities of body or implanted directly in the tissues. In systemic radiotherapy radioisotopes are administered orally or intravenously. Of these three, external radiotherapy is the most used because it allows planning of radiotherapy in three dimensions (3D), starting from a CT scan of the tumor region. Computed tomography planning allows the distribution of radiation in the tissues to be more accurate thus avoiding, that healthy tissues are affected. In our case, conventional external radiotherapy was implemented and executed for a prostate treatment with metal implants, using 4 irradiation fields (0, 90, 180, 270 degrees) and a total planned dose of 70 Gy fractioned in 35 sessions each with 2 Gy. In any type of treatment involving ionizing radiation, quality control (QC) is required to determine if the dose initially planned is delivered or not to the tumor. Ideally, a quality control should be implemented in three dimensions but to date there is no consolidated 3D dosimeter system in the clinic routine. However, the used of polymeric gels associated with magnetic resonance image (IRM) allow three-tridimensional dosimetry. In this context, the 3D dosimetry is applied using the magic gel with formaldehyde (magic-f). In addition to 3D dosimetry, absorbed dose measurements were performed by means of a dose in a point, using thermoluminescent and alanine dosimeters. The comparison of dose distributions calculated by TPS and measured in the gel was made using by gamma analysis (3% / 3mm), in this case, the distribution of dose measurement agrees with the distributions expected by TPS. The analysis shows a percentage of approval of 93%. The absorbed dose values at the bone-metal interface determined by the TL dosimeters, presented a 1.73 Gy increase in the region of the sacral bone, and another increases between 0,16 and 0,33 Gy were found in the regions as the head of the femur and the hip. These dose increases were only for two sessions with doses delivered to the phanton of 2 Gy. Similarly for alanine dosimeters were found increases in the dose of 1.22 and 2.42 Gy in the region of sacral bone. The planning done in this case was 6 Gy. The results evidently show how the inomogeneities of a material with a high atomic number generate disturbances over the initially planned dose distributions.

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22

Trapp, Jamie Vincent. "Imaging And Radiation Interactions Of Polymer Gel Dosimeters." Queensland University of Technology, 2003. http://eprints.qut.edu.au/15904/.

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Aim: The past two decades have seen a large body of work dedicated to the development of a three dimensional gel dosimetry system for the recording of radiation dose distributions in radiation therapy. The purpose of much of the work to date has been to improve methods by which the absorbed dose information is extracted. Current techniques include magnetic resonance imaging (MRI), optical tomography, Raman spectroscopy, x-ray computed tomography (CT) and ultrasound. This work examines CT imaging as a method of evaluating polymer gel dosimeters. Apart from publications resulting from this work, there has been only two other journal articles to date reporting results of CT gel dosimetry. This indicates that there is still much work required to develop the technique. Therefore, the aim of this document is to develop CT gel dosimetry to the extent that it is of use to clinical and research physicists. Scope: Each chapter in this document describes an aspect of CT gel dosimetry which was examined; with Chapters 2 to 7 containing brief technical backgrounds for each aspect. Chapter 1 contains a brief review of gel dosimetry. The first step in the development of any method for reading a signal is to determine whether the signal can actually be obtained. However, before polymer gel dosimeters can be imaged using a CT scanner, imaging techniques are required which are employable to obtain reliable readings. Chapter 2 examines the various artifacts inherent in CT which interfere with the quantitative analysis of gel dosimeters and a method for their removal is developed. The method for artifact reduction is based on a subtraction technique employed previously in a feasibility study and a system is designed to greatly simplify the process. The simplification of the technique removes the requirement for accurate realignment of the phantom within the scanner and the imaging of calibration vials is enabled. Having established a method by which readings of polymer gel dosimeters can be obtained with CT, Chapter 3 examines the CT dose response. A number of formulations of polymer gel dosimeter are studied by varying the constituent chemicals and their concentrations. The results from this chapter can be employed to determine the concentration of chemicals when manufacturing a polymer gel dosimeter with a desired CT dose response. With the CT dose response characterised in Chapter 3, the macroscopic cause of the CT signal is examined in Chapter 4. To this end direct measurement of the linear attenuation coefficient is obtained with a collimated radiation source and detector. Density is measured by Archimedes' principle. Comparison of the two results shows that the cause of the CT signal is a density change and the implications for polymer gel dosimetry are discussed. The CT scanner is revisited in Chapter 5 to examine the CT imaging techniques required for optimal performance. The main limitation of the use of CT in gel dosimetry to date has been image noise. In Chapter 5 stochastic noise is investigated and reduced. The main source of non-stochastic noise in CT is found and imaging techniques are examined which can greatly reduce this residual noise. Predictions of computer simulations are verified experimentally. Although techniques for the reduction of noise are developed in Chapter 5, there may be situations where the noise must be further reduced. An image processing algorithm is designed in Chapter 6 which employs a combination of commonly available image filters. The algorithm and the filters are tested for their suitability in gel dosimetry through the use of a simulated dose distribution and by performing a pilot study on an irradiated polymer gel phantom. Having developed CT gel dosimetry to the point where a suitable image can be obtained, the final step is to investigate the uncertainty in the dose calibration. Methods used for calibration uncertainty in MRI gel dosimetry to date have either assumed a linear response up to a certain dose, or have removed the requirement for linearity but incorrectly ignored the reliability of the data and fit of the calibration function. In Chapter 7 a method for treatment of calibration data in CT gel dosimetry is proposed which allows for non-linearity of the calibration function, as well as the goodness of its fit to the data. Alternatively, it allows for the reversion to MRI techniques if linearity is assumed in a limited dose range. Conclusion: The combination of the techniques developed in this project and the newly formulated normoxic gels (not extensively studied here) means that gel dosimetry is close to becoming viable for use in the clinic. The only capital purchase required for a typical clinic is a suitable water tank, which is easily and inexpensively producible if the clinic has access to a workshop.

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23

Sánchez, Mirko Salomón Alva. "Verificação 3D da distribuição da dose em radiocirurgia estereotáxica através de simulação Monte Carlo e dosimetria por ressonância magnética nuclear." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-15052013-193530/.

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A radiocirugia estereotáxica é uma técnica que fornece altas doses de radiação utilizando campos pequenos para conformação da dose no volume alvo do tratamento. Devido à complexidade desta técnica torna-se necessária a verificação da distribuição de dose no volume de tratamento. Neste trabalho, as distribuições tridimensionais (3D) de doses de casos clínicos de neoplasias cranianas foram estudadas utilizando-se um objeto simulador de cabeça. A reconstrução das distribuições de doses nos volumes alvo e nas regiões adjacentes a estes foram avaliadas com o código de simulação PENELOPE, o dosímetro MAGIC-f gel e com o sistema de planejamento iPlan. Filmes radiocrômicos também foram empregados para a determinação das distribuições de dose em planos do tratamento. As respostas obtidas com as ferramentas dosimétricas utilizadas foram analisadas através de distribuições de índices gama, comparando-se os mapas centrais das distribuições de dose obtidas com as quatro ferramentas dosimétricas utilizadas. Usando-se critérios de tolerância de 3% e 3mm, a análise realizada na região da prescrição de dose (isodoses de 95%) mostrou-se equivalente para todas as ferramentas dosimétricas utilizadas; resultado diferente foi observado para isodoses menores, com uma equivalência máxima de 76,5%. As distribuições volumétricas, obtidas através do PENELOPE, MAGIC-f gel e o iPlan, foram comparadas, ainda, através dos histogramas dose-volume, para cada caso estudado, mostrando que 95% da dose absorvida relativa encontra-se dentro do volume alvo para todos os planos estudados. A probabilidade de controle tumoral, TCP, foi avaliada para os casos de radiocirurgia estudados, a partir das distribuições volumétricas de dose, resultando em uma probabilidade de controle tumoral máxima de 72%, para todos os casos, conforme o modelo matemático de TCP utilizado. Das comparações realizadas pode-se inferir que o dosímetro MAGIC-f gel e o código de simulação PENELOPE-Monte Carlo podem ser utilizados para determinar as distribuições de dose em 3D para a técnica de radiocirurgia estereotáxica. Essas ferramentas dosimétricas podem, dessa forma, auxiliar no comissionamento de unidades de terapia e em verificações 3D de doses do tratamento dos pacientes, permitindo avaliações dentro e ao redor do volume alvo e podendo se tornar ferramentais de rotina nos serviços de radioterapia.
Stereotactic radiosurgery is a technique which delivers high radiation doses using small fields to conform the absorbed dose into the target volume. Due to the complexity of this technique it is necessary to verify the dose distribution in the treatment volume. Thus, in this study the three-dimensional (3D) dose distributions of selected clinical cases of cranial tumors were obtained using a head phantom. The the dose distributions of target volumes and adjacent regions were evaluated with PENELOPE Monte Carlo simulation code, MAGIC-f dosimeter and iPlan® treatment planning system. Radiochromic films were also used to determine the dose distribution on selected plans of the treatment. The obtained results for the proposed dosimetric tools were analyzed by the gamma index distributions, comparing the maps of the central dose distributions obtained with the four dosimetric tools. Using the dose criteria of 3% in 3 mm, the gamma index test showed equivalence in the region of dose prescription (95% isodose) and a different result was observed for lower isodoses, with maximum accordance of 76.5%. The volumetric dose distributions obtained with PENELOPE, MAGIC-f and iPlan were also compared using the dose-volume histograms for each studied case, showing that 95% of the absorbed dose yield within the target volume. The tumor control probability, TCP, was evaluated for the studied radiosurgery cases, from the dose distributions-volumetric, resulting in a maximum probability of tumor control of 72% for all cases, for the used mathematical model of TCP. From the results it can be inferred that the MAGIC-f gel dosimeter and the PENELOPE Monte Carlo simulation code can be used to determine 3D dose distributions for stereotactic radiosurgery. These dosimetric tools can assist the commissioning of treatment units and 3D dose verifications of patients treatments, allowing assessments in and around the target volume and may become routine in radiotherapy services.

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24

MANGUEIRA, THYAGO F. "Avaliacao dosimetrica da solucao fricke gel usando a tecnica de espectrofotometria para aplicacao na dosimetria de eletrons e neutrons." reponame:Repositório Institucional do IPEN, 2009. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9447.

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Made available in DSpace on 2014-10-09T12:26:53Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T14:00:05Z (GMT). No. of bitstreams: 0
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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25

Schwarcke, Marcelo Menna Barreto. "Caracterização do gel polimérico MAGIC-f para aplicação em medicina nuclear utilizando imagens de ressonância magnética." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-12112013-084219/.

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Este trabalho visa aprimorar e tornar mais precisa a utilização do dosímetro gel polimérico MAGIC-f no estudo da distribuição de dose para fonte radioativas utilizadas na terapia e diagnóstico em medicina nuclear. Para isso foram avaliados os parâmetros de leitura do gel em equipamentos de ressonância magnética e sua resposta quando comparado a resultados obtidos através da utilização do código PENELOPE de simulação Monte Carlo. Dentre as incertezas observadas no processo global da utilização do gel MAGIC-f, sua manufatura foi a que demonstrou uma maior preocupação uma vez que erro na frações de componentes químicos adicionados ocasiona grande diferença na resposta do dosímetro. A aquisição da informação dosimétrica em um equipamento de imagem por ressonância magnética demonstrou que tempos ao eco mais curtos são mais eficientes na diferenciação do sinal gerado no processo de polimerização devido a utilização de fontes de medicina nuclear do que ajustes na resolução da imagem e que a homogeneidade de campo magnético pode ocasionar grande alteração nos valores obtidos. Experimentos realizados com o gel MAGIC-f, demonstraram um baixa dependência energética e um grande dependência com a taxa de dose, dois fatores importantes em medicina, mas resultados simulados e experimentais comparativos utilizando fontes de I-131, Tc-99m e F-18, demonstraram uma grande precisão nos resultados apresentados, tornando assim o gel MAGIC-f uma excelente ferramenta na verificação volumétrica da dose absorvida na terapia com fontes de medicina nuclear.
This work aims to improve and make more accurate use of the gel dosimeter MAGIC-f polymer in the study of dose distribution for radioactive source used in therapy and diagnosis in nuclear medicine. For this, MRI parameters reading of the gel were evaluated and its response when compared to results obtained using a Monte Carlo simulation PENELOPE code. Among the uncertainties observed in the overall use of MAGIC-f gel, its manufacturing demonstrated a greater concern since error in chemical fractions added causes big difference in the response of the dosimeter. The acquisition of dosimetric equipment information in a magnetic resonance imaging showed that the shorter eco times are more efficient in differentiating the signal generated in the polymerization process due to the use of sources of nuclear medicine than image resolution changes and the homogeneity of the magnetic field can cause large difference in the results. Experiments performed with the MAGIC-f gel, demonstrated a low energy dependence and a large dependence on the dose rate, two important factors in nuclear medicine, but comparative results with simulated and experimental processes using sources of I-131, Tc-99m and F-18 showed a great accuracy in results, thus making the MAGIC-f gel an excellent tool for volumetric verification of absorbed dose therapy with sources of nuclear medicine.

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26

Sandwall, Peter A. II. "Spatial Dosimetry with Violet Diode Laser-Induced Fluorescence of Water-Equivalent Radio-Fluorogenic Gels." Thesis, University of Cincinnati, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3625827.

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The following work describes investigations of spatial dosimetry using laser-induced fluorescence of a radio-fluorogenic detector embedded within water-equivalent media. The chemical composition of a gelatin-based coumarin-3-carboxylic acid detector was investigated and dose response characterized. Violet diode (405nm) excitation sources were explored and laser-induced fluorescence (LIF) employed to obtain the pattern of fluorescent emission yielding images of the integrated spatial dose distribution. The design of a three-dimensional reader is proposed to provide a foundation for future work.

Radio-fluorogenic processes create fluorescent products in response to ionizing radiation. Water radiolysis produced by ionizing radiation yields hydroxyl free radicals that readily hydroxylate coumarin-3-carboxylic acid to 7-hydroxy-coumarin-3-carboxylic acid, a derivative of umbelliferone. Umbelliferone is a known fluorophore, exhibiting peak excitation in the UV to near UV range of 365-405nm with a visible 445nm blue emission. Coumarin-3-carboxlyic acid has been studied in an aqueous gelatin matrix.

The radio-fluorogenic coumarin-gelatin detector has been shown to respond to an absorbed dose of ionizing radiation in a measureable manner. The detector was studied with respect to concentration of gelatin and coumarin in the presence of pH buffers. Dose response of the detector was investigated with regard to ionizing radiation type, energy, and rate of irradiation. Results demonstrate a functional detector.

Patterns of energy deposition were formed in response to ionizing radiation produced by a sealed-source of radioactive Ir-192 embedded in the gelatin matrix of the detector. Spatial distributions of absorbed dose were recorded and analyzed as a function of fluorescent emission. The distribution of energy deposition was imaged with LIF excitation by a divergent beam of 405nm light and determined by analysis of digital image pixel intensity values displaying the 445nm fluorescent emission. Results demonstrate spatial dosimetry proof of principle.

A basic dedicated reader system was fabricated employing LIF. Images of fluorescent emission excitation profiles were obtained in multiple aqueous samples and processed to obtain a dose response. Design of an optical reader system for the radio-fluorogenic detector is explained and a three-dimensional dosimetry system proposed. Three-dimensional imaging principles with LIF have been illuminated.

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27

Venning, Anthony James. "Investigation of radiation sensitive normoxic polymer gels for radiotherapy dosimetry." Queensland University of Technology, 2006. http://eprints.qut.edu.au/16257/.

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The overall objective of this study was to develop and characterise new normoxic polymer gel formulations for evaluation of complex 3-D treatment volumes for application in radiotherapy dosimetry. Throughout this thesis, the essential characteristics of normoxic polymer gels have been extensively investigated. Studies were performed on the chemical components of the MAGIC gel and an improved formulation was proposed. Various anti-oxidants were studied and different versions of the MAGIC gel with fewer chemicals were developed and named MAGAS and MAGAT gel dosimeters. The ascorbic acid anti-oxidant was found to have a slow oxygen scavenging rate and therefore a delay period between manufacture and irradiation of the MAGAS gel was necessary before the gel became radiation sensitive. Vacuum pumping on the MAGAS gel solution to remove dissolved oxygen was shown to initially increase the R2-dose response and sensitivity of the dosimeter, reducing the time between manufacture and irradiation. Studies of the MAGAS gel for measurement of depth dose showed that MAGAS gel has potential as a clinical radiotherapy dosimetry tool. The radiological properties of MAGIC, MAGAS and MAGAT gels were investigated. Due to their high gelatine and monomer concentration, differences with water were observed for the cross-section ratios for attenuation, energy absorption and collision stopping power coefficient ratios through the therapeutic energy range. It was determined that when using and developing normoxic polymer gels the most important consideration for radiological water equivalence are the mass and relative electron densities. A preliminary study was performed with the hypoxic PAG gel dosimeter combined with tetrakis (hydroxymethyl) phosphonium chloride anti-oxidant to form a normoxic PAG gel dosimeter named PAGAT gel. It was found PAGAT gel compared favourably with previous studies of the hypoxic PAG gel. An extensive study was subsequently undertaken in which PAGAT gel was investigated for a number of essential characteristics. The PAGAT gel formulation showed potential as a normoxic polymer gel for clinical radiotherapy dosimetry, which has a significantly reduced manufacturing time and procedure compared with the hypoxic PAG gel dosimeter. The radiological attenuation properties of the PAGAT and MAGAT gels were investigated as a feasibility study for using x-ray computerised tomography (CT) as an evaluation technique of normoxic polymer gels. CT was shown to have potential as an evaluation tool for measuring the dose response of normoxic polymer gel dosimeters. An investigation was performed on the CT diagnostic dose response of normoxic polymer gels. Normoxic polymer gels were found to have potential for use as a specialised tool in measuring computerised tomography dose index (CTDI) for acceptance testing and quality assurance of CT scanners in diagnostic radiology. These findings provide a significant contribution toward the development and successful implementation of normoxic polymer gel dosimetry to clinical radiotherapy.

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Silva, Ana Luiza Quevedo Ramos da. "Avaliação de parâmetros dosimétricos de fontes de braquiterapia utilizando simulação Monte Carlo e dosimetria gel polimérica." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-06102014-084506/.

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A dosimetria em braquiterapia é importante para garantir a igualdade entre a dose entregue ao paciente e a dose planejada, porém a determinação experimental da dose é difícil devido ao alto gradiente de dose em regiões próximas à fonte. Nesse sentido, a dosimetria gel polimérica têm sido estudada como forma de se obter a distribuição tridimensional das doses dessas fontes. O protocolo da Associação Americana de Físicos em Medicina, intitulado TG-43, propõe um formalismo para o cálculo de dose de fontes de braquiterapia através de parâmetros da atividade, anisotropia e geometria da fonte, além de atenuação e espalhamento da radiação produzida pela fonte. Porém, a determinação das funções dosimétricas necessárias para o cálculo da dose não é feita diretamente através de experimentos. Nessa linha, o Método Monte Carlo vêm sendo utilizado no cálculo dessas funções dosimétricas em braquiterapia. Neste trabalho, foram determinados os parâmetros dosimétricos de duas fontes de braquiterapia, 60Co e 192Ir, utilizando simulação Monte Carlo com o código PENELOPE, assim como as distribuições de dose utilizando dosimetria gel polimérica com o MAGIC-f. Os dados obtidos computacionalmente foram comparados com a literatura, obtendo-se concordância melhor que 98% em todos os parâmetros para a fonte de 60Co. Para a fonte de 192Ir, encontraram-se diferenças de até 22%, embora quando os resultados deste trabalho foram comparados com o sistema de planejamento, o ajuste utilizado para o conjunto de pontos possui R2 de 0,9996. A comparação das distribuições de dose da fonte de 192Ir simuladas e determinadas com o gel polimérico MAGIC-f, apresentou concordância de 97% nos pontos englobados pela isodose de 50%, quando o critério de 3% e 3 mm foi utilizado. Esses resultados evidenciam o potencial do uso da dosimetria gel polimérica e da simulação Monte Carlo com o código PENELOPE em dosimetria de fontes de braquiterapia de alta taxa de dose.
Dosimetry in brachytherapy is important to assure the conformity between the planned and the delivered dose to the patient. However, the experimental determination of dose is difficult in this technique due the high dose gradient in regions near the source. Hence, polymer gel dosimetry has been studied as a tool to obtain three-dimensional distribution dose for these sources. A report of American Association of Medical Physics, entitled TG-43, proposes a formalism for dose calculation for brachytherapy sources through parameters such as activity, anisotropy and geometry of the source, and the attenuation and radiation scattering produced in the surrounding medium. However, the dosimetric functions needed for dose calculations are not directly determined through experiments. In this concern, the Monte Carlo method has been used in the calculation of these dosimetric funcions in brachytherapy. In the present work, the dosimetric parameters for two brachytherapy sources, 60Co e 192Ir, were determined using Monte Carlo simulation with PENELOPE code, and the dose distributions for the 192Ir source were determined using polymer gel dosimetry with MAGIC-f. Data obtained computationally were compared to literature, showing more than 98% agreement in all parameters for the 60Co source. For 192Ir, differences up to 22% were found to the literature, although when the results of this work were compared to the treatment planning system, a R2 equal to 0,9996 was found to the data fitting adjusting both data. The comparison of simulated dose distributions for 192Ir and those determined with MAGIC-f polymer gel showed that 97% of the points covered by 50% isodose are in agreement when gamma index criteria of 3% and 3 mm was used. These results indicate the potential use of polymer gel dosimetry with MAGIC-f and Monte Carlo simulation with PENELOPE code in dosimetry of high dose rate brachytherapy sources.

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Lizar, Jéssica Caroline. "Comparação dosimétrica 3D de tratamentos de câncer de mama com técnica conformacional 3D usando filtros e com IMRT direto e inverso na presença do movimento respiratório." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-30082017-152201/.

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A radioterapia externa pós-operatória em mulheres diagnosticadas com câncer de mama em estágio inicial é tido como um procedimento padrão, no entanto durante o planejamento para irradiação do volume alvo as possíveis incertezas dosimétricas introduzidas dado o movimento respiratório intrínseco da paciente são desconsideradas. Este estudo avalia não apenas a influência da respiração na distribuição tridimensional da dose, mas como essa distribuição se modifica dado a técnica radioterápica empregada para o tratamento. Três técnicas de planejamento foram analisadas: a radioterapia conformacional tridimensional (3D-RT) com filtros, a radioterapia com intensidade modulada (IMRT) usando planejamento direto e o IMRT inverso. A fim de simular o movimento de contração e expansão da caixa torácica, utilizou-se uma plataforma com amplitudes de oscilação pré-determinadas, sendo a frequência de oscilação provida por uma fonte de tensão variável. Para simular a mama usou-se objetos simuladores semiesféricos preenchidos com gel dosimétrico (MAGIC-f). Os planejamentos para cada técnica foram realizados sobre a mesma tomografia computadorizada (CT) do objeto simulador preenchido com água no modo estático. Foram produzidos três lotes de dosímetro gel para o projeto, cada lote foi irradiado com uma técnica radioterápica diferente, sendo que cada lote inclui cinco objetos simuladores e um conjunto de nove tubos de calibração preenchidos com gel MAGIC-f. O primeiro dos objetos simuladores é utilizado como referência, o segundo é irradiado no modo estático, os demais são irradiados em diferentes amplitudes, respectivamente: 0,34 cm, 0,88 cm e 1,22 cm. A informação volumétrica de dose foi obtida utilizando imagens por ressonância magnética nuclear (IRMN), para cada lote foram adquiridos IRMN com sequência multi spin echo e os mapas de relaxometria, que são associados à dose, foram extraídos em um software desenvolvido e aprimorado pelo nosso grupo de pesquisa. A comparação quantitativa dos mapas de relaxometria dos objetos simuladores em movimento em relação ao modo estático foi realizado pelo índice gamma tridimensional (3% / 3mm / 15% Threshold). Para o 3D-RT a porcentagem de pontos aprovados do objeto estático em relação ao oscilante na amplitude de 0,34 cm foi de 96,44%, para amplitude de 0,88 cm foi de 93,23% e para amplitude de 1,22 cm foi de 91,65%. Para o IMRT direto a porcentagem de pontos aprovados do objeto estático em relação ao oscilante na amplitude de 0,34 cm foi de 98,42%, para amplitude de 0,88 cm foi de 95,66% e para amplitude de 1,22 cm foi de 94,31%. Para o IMRT inverso a porcentagem de pontos aprovados do objeto estático em relação ao oscilante na amplitude de 0,34 cm foi de 94,49%, para amplitude de 0,88 cm foi de 93,51% e para amplitude de 1,22 cm foi de 86,62%. A partir dos resultados, infere-se que a movimentação respiratória de baixa amplitude, para tratamentos de câncer de mama, não é um fator preocupante para a rotina clínica, porém o aumento da amplitude da oscilação aumenta a inomogeneidade de dose e pode afetar os parâmetros dosimétricos da cobertura do volume alvo em relação ao planejamento do tratamento. Observou-se em conjunto que a distribuição de dose se modifica claramente com a técnica em uso e no caso do IMRT inverso para amplitude de oscilação de 1,22 cm a aprovação no índice gamma foi menor que 90%
External postoperative radiotherapy in women diagnosed with early stage breast cancer is considered as a standard procedure, however during planning for target volume irradiation as possible dosimetric uncertainties reabsorption of the patient\'s intrinsic respiratory movement are disregarded. This study evaluates not only the influence of respiration on the three-dimensional distribution of the dose but how this distribution is modified due to the radiotherapy technique used for treatment. Three planning techniques were analyzed: three-dimensional conformational radiotherapy (3D-RT) with filters, intensity-modulated radiotherapy (IMRT) using direct planning and inverse IMRT. In order to simulate the movement of contraction and expansion of the chest wall, a platform with predetermined oscillation amplitudes was used, the oscillation frequency was provided by a variable voltage source. To simulate the breast, semi-spherical simulator objects filled with dosimetric gel (MAGIC-f) were used. The plannnings for each technique were performed on the computerized tomography (CT) of the simulator object filled with water in static mode. Three batches of gel dosimeters were prepared for the project, each batch was irradiated with a different radiothermic technique and comprised five simulator objects and a set of nine calibration tubes filled with MAGIC-f gel. The first simulator objects is used as reference, the second is irradiated in the static mode, the others are irradiated using different amplitudes, respectively: 0,34 cm, 0,88 cm and 1,22 cm. Volumetric dose information was obtained using Nuclear Magnetic Resonance Imaging, each batch was scanned with a multi spin echo sequence and the dose-related relaxometry maps were extracted in a software developed and improved by our Group of research. The quantitative comparison of the relaxometry maps of the moving simulator objects with respect to the static mode was performed by the three-dimensional gamma index (3% / 3mm / 15% threshold). For the 3D-RT, the percentage of approved points of the static object with respect to the oscillator in the amplitude of 0.34 cm was 96.44%, for amplitude of 0.88 cm was 93.23% and for amplitude of 1.22 cm was 91.65%. For the direct IMRT the percentage of approved points of the static object in relation to the oscillator in the amplitude of 0.34 cm was 98.42%, for amplitude of 0.88 cm was 95.66% and for amplitude of 1.22 cm was 94.31%. For the inverse IMRT, the percentage of approved points of the static object in relation to the oscillator in the amplitude of 0.34 cm was 94.49%, for amplitude of 0.88 cm was 93.51% and for amplitude of 1.22 cm was 86.62%. From the results, it is inferred that a low-amplitude respiratory movement, for breast cancer treatments, is not a worrying factor for clinical routine, however, increasing the amplitude of the oscillation increases the inomogeneity of the dose and this affects the dosimetry parameters of the target volume coverage. It was observed that the dose distribution changes with the technique in use and in the case of the inverse IMRT for amplitude of oscillation of 1.22 cm, less than 90% of points were approved in the gamma index evaluation

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30

Paudel, Nava R. "Nanoparticle-aided Radiation Therapy: Micro-dosimetry and Evaluation of the Mediators Producing Biological Damage." University of Toledo / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1403142628.

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31

Meesat, Ridthee. "Evaluation of the radiosensitizing or radioprotective/antioxidant potential of some selected compounds by polyacrylamide gel dosimetry and Fricke dosimeter, and utilization of the femtosecond infrared laser pulse filamentation as a novel, powerful beam for cancer radiotherapy." Thèse, Université de Sherbrooke, 2012. http://hdl.handle.net/11143/6246.

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In radiation treatment, a sufficiently high radiation dose must be delivered to the tissue volumes containing the tumor cells while the lowest possible dose should be deposited in surrounding healthy tissue. We developed an original approach that is fast and easy to implement for the early assessment of the efficiency of radiation sensitizers and protectors. In addition, we characterized a new femtosecond laser pulse irradiation technique. We are able to deposit a considerable dose with a very high dose rate inside a well-controlled macroscopic volume without deposition of energy in front or behind the target volume. The radioprotective efficiency was measured by irradiation of the Fricke solution incorporating a compound under study and measuring the corresponding production of ferric ions G (Fe3+ ). The production of ferric ions is most sensitive to the radical species produced in the radiolysis of water. We studied experimentally and simulated with a full Monte-Carlo computer code the radiation-induced chemistry of Fricke/cystamine solutions. Results clearly indicate that the protective effect of cystamine originates from its radical-capturing ability, which allows this compound to compete with the ferrous ions for the various fre radicals - especially · OH radicals and H· atoms - formed during irradiation of the surrounding water. The sensitizing capacity of radiation sensitizers was measured by irradiation of a polyacrylamide gel (PAG) dosimeter incorporating a compound under study and measuring the corresponding increase in the gradient between spin-spin relaxation rate (R2 ) and absorbed dose. We measured an irradiation energy-dependent increase in R 2 -dose sensitivity for halogenated compounds or a decrease for radioprotectors. Finally, we studied a novel laser irradiation method called "filamentation". We showed that this phenomenon results in an unprecedented deposition of energy and the dose rate thus achieved exceeds by orders of magnitude values previously reported for the most intense clinical radiotherapy systems. Moreover, the length of the dose-fre entrance region was adjusted by selecting the duration of femtosecond laser pulses. In addition, we provided evidence that the biological damage caused by this irradiation was similar to other ionizing radiation sources. [symboles non conformes]

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SILVA, CLEBER F. "Avaliacao dosimetrica da resposta espectrofotometrica da solucao gel de alanina para radiacao gama, de fotons de eletrons e de neutrons termicos." reponame:Repositório Institucional do IPEN, 2009. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9441.

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Made available in DSpace on 2014-10-09T12:26:49Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T14:00:10Z (GMT). No. of bitstreams: 0
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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33

Bleuse, Olivier. "Développement de la lecture optique par lumière diffusée des gels dosimétriques." Thesis, Bourgogne Franche-Comté, 2018. http://www.theses.fr/2018UBFCE018.

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Les techniques les plus avancés en radiothérapie sont aujourd’hui devenu des standards dans les traitements des tumeurs malignes. Or ces techniques modernes ont la particularité de fournir des distributions complexes de la dose afin de cibler au mieux le volume tumoral à traiter et de protéger au mieux le tissu sain avoisinant le volume cible. Par conséquent, le problème de l’assurance qualité prend de plus en plus d’importance dans les unités de radiophysique au sein des services de radiothérapie. Pour pallier au manque des détecteurs actuels, une approche en trois dimensions est nécessaire pour garantir la qualité des traitements. Plusieurs techniques sont en cours de développement, notamment celles des gels dosimétriques. Cependant les techniques de lecture sont soumises à différentes types d’artéfacts limitants leurs intégrations dans les pratiques courantes. Ce travail a consisté à développer une nouvelle technique de lecture optique dédiée aux gels dosimétriques, notamment les gels de polymère. Cette méthode basée sur la mesure de l’intensité diffusée utilise une approche sphérique des domaines radioformés. En utilisant la technique du taux de polarisation, le prototype développé propose de lier l’intensité diffusée à une particule sphérique homogène dont la taille évolue en fonction de la dose absorbée. Pour démontrer cette approche de faisabilité, une caractérisation des gels de polymère a été réalisée, notamment l’étude de l’indice de réfraction en fonction de la dose absorbée. Ces informations ont permis de réaliser des modélisations numériques qui ont été ensuite confrontées à l’expérimentation
The most advanced techniques in radiotherapy have now become standard in the treatment of malignant tumors. However, these modern techniques have the particularity of providing complex distributions of the dose in order to better target the tumor volume to be treated and to better protect the healthy tissue surrounding the target volume. As a result, the problem of quality assurance is becoming increasingly important in radiophysics units within radiotherapy departments. To overcome the lack of current detectors, a three-dimensional approach is necessary to guarantee the quality of treatments. Several techniques are under development, including dosimetric gels. However, reading techniques are subject to different types of artifacts limiting their integration into daily uses.This work consisted to develop a new optical reading technique dedicated to dosimetric gels, especially polymer gels. This method based on the measurement of scattered intensity uses a spherical approach of radioformed domains.Using the polarization rate technique, the developed prototype proposes to link the scattered intensity of an homogeneous spherical particle whose size evolves as a function of the absorbed dose. To demonstrate this feasibility approach, a characterization of the polymer gels was carried out, in particular the study of the refractive index as a function of the absorbed dose. This information made it possible to carry out numerical modeling which was then confronted to the experimentation

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Oliveira, Paulo Marcio de. "Avaliação de dose nos sistemas de irradiação de bolsas de sangue para esterilização." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/85/85131/tde-14112014-142426/.

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O procedimento de esterilização do sangue é adotado para que sejam mínimas as condições necessárias de manifestação da doença do enxertoversus- hospedeiro associada à transfusão de sangue (DECHT), síndrome, geralmente fatal. Neste trabalho foi utilizada a solução Fricke gel desenvolvida no IPEN para a obtenção de um objeto simulador de bolsa de sangue empregada no processo de irradiação para esterilização de sangue em um irradiador Gammacell Elan. O objetivo desse trabalho é determinar a homogeneidade da dose aplicada no processo de esterilização de bolsas de sangue. Foram utilizadas as técnicas de Espectrofotometria de Absorção Óptica (EAO), Densitometria Óptica (DO), Termoluminescência (TL) e Ressonância Magnética por Imagem (RMI) e os softwares Numaris® versão 4 (Syngo-MR-A30) e MatLab® (versão 9.0) para a aquisição e reconstrução das imagens. O estudo foi realizado posicionando no canister do irradiador inicialmente uma bolsa e, posteriormente, duas bolsas e três bolsas e aplicando uma dose nominal de 25 Gy. O fabricante do irradiador Gammacell Elan recomenda que seja irradiado em cada procedimento o valor máximo de três bolsas de sangue. Os resultados obtidos indicam que o irradiador Gammacell Elan não demostrou homogeneidade na distribuição da dose. Irradiando uma bolsa de sangue foi obtida uma diferença de dose de 3,65 %, enquanto para duas bolsas de sangue essa diferença caiu para 2,65 % e quando posicionadas três bolsas de sangue a diferença de dose foi de 1,88 %. O tempo de abertura de fechamento do equipamento de irradiação é responsável pela diferença de dose 3,17 % acima da dose prevista à realização das irradiações de bolsas de sangue. Os resultados obtidos usando o filme radiocrômico Grafchromic MD-55 de dupla face aplicada à avaliação de dose no sistema de rotação de irradiação não apresentou resultados reproduzíveis.
The blood sterilization procedure is adopted so that the necessary conditions of manifestation of graft-versus-host syndrome, disease associated with blood transfusion (AT-GVHD), usually a fatal disease, are minimal. In this work the Fricke gel solution developed in IPEN was used for obtaining a phantom of blood bag used in the irradiation process for sterilization of blood in a Gammacell irradiator Elan. The objective of this study was to evaluate the homogeneity of the applied radiation sterilization dose in the blood bags. Optical Absorption Spectroscopy (OAS), Optical Densitometry (OD), Thermoluminescence (TL) and Magnetic Resonance Imaging (MRI) technics and Numaris® software version 4 (Syngo-MR-A30) and MatLab® (version 9.0) softwares were used to images acquisition and reconstruction. The study was conducted positioning one bag in the canister irradiator initially and subsequently two and three bags together and applying a nominal dose of 25 Gy. The Elan Gammacell irradiator manufacturer recommends that the maximum values of three blood bags are irradiated in each procedure. The results indicate that the Gammacell irradiator Elan did not presents homogeneous dose distribution. Radiating a blood bag a dose difference of 3.65 % was obtained, while for two bags of blood that difference dropped to 2.65% and when positioned three blood bags the difference in dose was 1.88 %. The opening and closing times of the irradiation source is responsible for an increasing in the planned irradiation dose of 3.17%. The results obtained using radiochromic double-sided Grafchromic MD-55 film applied to dose evaluation in the rotation irradiation system did not present reproducible results.

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Lima, Hestia Raissa Batista Reis. "Síntese e caracterização do LiAlSi2O6 por novas rotas de produção." Universidade Federal de Sergipe, 2013. https://ri.ufs.br/handle/riufs/5311.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
The spodumene (LiAlSi2O6 - LAS) is a silicate that has shown good results for high-dose dosimetry for gamma rays. This silicate may be obtained naturally or synthetically. The synthetic spodumene has been produced by solid state reaction, whose difficulty arises from the need to employ high temperatures. This paper aims to produce LAS through two different production routes: the proteic sol-gel and Pechini methods. The material produced was characterized by X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravimetry (TGA) in order to evaluate the structural properties of the material, as well as possible changes in physical or chemical properties depending on the temperature. It was found by XRD and Rietveld refinement was possible to obtain LAS B-spodumene phase by both methods. The thermal analysis showed that the material for both methods suffer considerable loss of weight in the temperature range 20-600 °C. Through thermoluminescent measures, one can observe that the LAS produced by both methods shows thermoluminescent peaks from beta irradiation at a dose of 1 Gy, thus allowing its application dosimetry. It can be concluded therefore that there is the possibility of producing them in large numbers at reduced cost and environmental impact, being viable in dosimetry. It also follows that the sol-gel protein appeared to be the best way to produce the LAS compared with other routes used, such as solid state synthesis or devitrification.
O espodumênio (LiAlSi2O6 LAS) é um silicato que tem demonstrado bons resultados para dosimetria de altas doses para raios gama. Esse silicato pode ser obtido de forma natural ou sintética. O espodumênio sintético tem sido produzido por reação do estado sólido, cuja dificuldade provém da necessidade de se empregar altas temperaturas. O presente trabalho tem o objetivo de produzir o LAS por meio de duas rotas de produção diferentes: a sol-gel proteica e método Pechini. O material produzido foi caracterizado através da difração de raios X (DRX), análises térmica diferencial (DTA) e termogravimétrica (TGA) com o intuito de avaliar as propriedades estruturais do material, bem como as possíveis mudanças de propriedades físicas ou químicas em função da temperatura. Verificou-se através da DRX e do refinamento Rietveld que foi possível se obter LAS na fase B-espodumênio por ambos os métodos. As análises térmicas mostraram que o material, por ambos os métodos, sofre perda considerável de massa no intervalo de temperatura de 20 a 600 °C. Através de medidas termoluminescentes, pode-se observar que o LAS produzido por ambos os métodos apresenta picos termoluminescentes a partir de irradiação beta com dose de 1 Gy, possibilitando sua aplicação dosimétrica. Pode-se concluir, assim, que há possibilidade de produção do LAS em larga escala a um custo e impacto ambiental reduzidos, sendo viável sua utilização em dosimetria. Também se conclui que o método sol-gel proteico se apresentou como sendo a melhor forma de produzir o LAS em comparação com outras rotas utilizadas, tais como síntese de estado sólido ou desvitrificação.

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Silveira, Matheus Antônio da. "Dosimetria gel no controle de qualidade tridimensional para radioterapia de intensidade modulada (IMRT) de próstata." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-03072014-233935/.

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A radioterapia de intensidade modulada (IMRT) é uma das mais modernas técnicas radioterapêuticas que permite a entrega de elevadas e complexas distribuição de doses ao volume tumoral, que necessita de novos métodos para o controle de qualidade dos procedimentos efetuados. Nos serviços de radioterapia costuma-se usar para o controle de qualidade do sistema de planejamento, a câmara de ionização para verificação pontual da dose e um dispositivo com diodos semicondutores (MapCHECK2) para a verificação bidimensional em um plano da fluência planejada, entretanto, para a verificação tridimensional dessas distribuições de doses ainda não há um dosímetro consolidado na rotina clínica. Nesse contexto, para a dosimetria tridimensional se destacam os géis poliméricos. Neste trabalho foram feitas a dosimetria convencional, pontual e bidimensional como se faz na rotina clínica e a dosimetria tridimensional utilizando o gel polimérico Magic-f, que apresenta a distribuição de dose volumétrica. Para este trabalho foi escolhido o tratamento de câncer de próstata, pois na atualidade é um dos tipos de cânceres mais comuns entre os homens. No contexto da dosimetria gel, para se obter a informação volumétrica é necessária uma técnica de imagem, no presente caso foram utilizadas imagens por ressonância magnética (magnetic resonance imaging, MRI). A partir dessas imagens é possível determinar as distribuições de doses processando-as em um software desenvolvido pelo grupo que determina as taxas de relaxação R2 associada à dose absorvida e posteriormente comparar as imagens obtidas com as imagens do sistema de planejamento. Para isso, se obteve dez cortes ao longo de cada simulador físico ou fantom em que sua comparação foi feita com a respectiva fatia do sistema de planejamento, na posição correspondente. Para uma avaliação quantitativa foi utilizado o conceito de índice gama, no critério padrão da radioterapia, 3% da dose e 3mm de distância de concordância. Os resultados obtidos com a dosimetria gel se mostram de acordo com os controles de qualidade convencionais e oferecem uma visão global da distribuição de dose no volume alvo.
The intensity modulated radiotherapy (IMRT) is one of the most modern radiotherapeutic technique that enables the delivery of high and complexes conformational doses to the tumor volume, that requires new methods for the quality assurance of the procedures performed. Radiotherapy services usually perform quality assurance of the planning system with the ionization chamber for spot-checking and an array of semiconductor diodes (MapCHECK2) to check on a two-dimensional plane, however for tridimensional dose verification does not exist an established dosimeter in the clinical routine. In this context, for three-dimensional dosimetry the polymeric gels were used. In This work the conventional one and two-dimensional dosimetry as employed in the clinical routine, and the three-dimensional dosimetry using polymer gel MAGIC- f, which provide the volumetric dose distribution. Prostate cancer clinical cases were chosen for this work because this kind of tumor is one of the most common cases in male individuals. In the context of dosimetry gel to obtain volumetric information an imaging technique is necessary, in this case the magnetic resonance imaging (MRI), was used to measure the dose. From these images it is possible to determine the distributions of doses processing them in a software developed by our research group that determines R2 relaxation rates associated with the absorbed dose and subsequently compare the images obtained with the images of the planning system. For this, ten slices were obtained along each phantom, and comparisons were made with the respective slice of the treatment planning system, in the corresponding position. For a quantitative evaluation of the gamma index , in the standard criterion in radiotherapy, 3 % dose and 3 mm distance to agreement was used. The results obtained shown that gel dosimetry agrees with the conventional quality controls and provide an overview of dose distribution in the target volume.

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Lama, Lucas Sacchini Del. "Caracterização e adaptação do dosímetro Fricke para dosimetria em irradiação de sangue." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-11112013-115906/.

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A Doença Enxerto Contra Hospedeiro Associada à Transfusão (DECH-AT) é uma reação transfusional rara, porém fatal, que ocorre devido à presença de células T no sangue doado e que pode ser prevenida por meio da irradiação do sangue do doador e de seus componentes antes da transfusão. Assim, o controle de qualidade associado à irradiação do sangue é necessário para se garantir a qualidade do produto transfundido. Neste trabalho é proposta a caracterização e a adaptação da resposta do dosímetro Fricke para uso na dosimetria da irradiação de sangue, mais especificamente o Fricke Xilenol Gel (FXG). Este é um dosímetro químico radiocrômico, que apresenta as vantagens de ser tecido equivalente e de permitir a inferência espacial da dose absorvida dentro da faixa de doses usados na prevenção DECH-AT. Dessa maneira, de modo a possibilitar a inferência de dose absorvida em todo o intervalo utilizado na prevenção da DECH-AT (25 a 50 Gy), o FXG foi caracterizado e adaptado para aplicações dosimétricas envolvendo a irradiação de sangue e derivados. Os resultados com o novo dosímetro apontaram adequabilidade para toda a faixa necessária de doses absorvidas, com sensibilidade e desvanecimento temporal satisfatórios para aplicações rotineiras. Além disso, pela metodologia proposta neste trabalho, foi possível determinar as distribuições espaciais das doses absorvidas com o dosímetro proposto de uma maneira rápida e simples, mostrando assim que este dosímetro apresenta características convenientes para o controle de qualidade para a dosimetria da irradiação de sangue e de hemocomponentes.
The Transfusion Associated Graft Versus Host Disease (TA-GVHD) is a rare transfusion reaction, however fatal, which develops due to the presence of donor T lymphocytes in the donated blood and that can be avoided by the irradiation of the donated blood blood and blood components prior to transfusion. Thus, the associated quality control of blood irradiation is necessary to guarantee the quality of the transfused product. In this work it is proposed the characterization and adaptation of the response of a Fricke dosimeter to be used for dosimetry of blood irradiation, more especiafically the Fricke Xylenol Gel (FXG). This is a radiochromic chemical dosimeter, which presents advantages to be tissue equivalent and allows the spatial absorbed dose inference. In this manner, in a way to possibilitate the absorbed dose inference in the full interval used for the prevention of the TA-GVHD (25 to 50 Gy) the FXG was characterized and adapted for dosimetry applications involving blood and blood components irradiation. The results with the new dosimeter showed adequability for the necessary absorbed doses, with satisfactory sensibility and time fading for routine applications. Furthermore, according to the methodology proposed in this work, it was possible to determine the spatial absorbed dose distributions with the new dosimeter in an fast and simple way, showing that this dosimeter presents convenient characteristics for dosimetry quality control of irradiated the blood and blood components.

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Baldock, Clive. "Aspects of dosimetry using radiation sensitive gels." Thesis, King's College London (University of London), 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249297.

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Zhang, Qing Jane. "Dynamic mathematical modeling of a polyacrylamide gel dosimeter." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/MQ63396.pdf.

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Gear, Jonathan. "Polymer gels for dosimetry in targeted radionuclide therapy." Thesis, Institute of Cancer Research (University Of London), 2009. http://publications.icr.ac.uk/10124/.

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This thesis Presents an investigation into the use of polymer gel dosimeters for analysis in targeted radionuclide therapy (TRT). The project aims to establish viability, technical issues, and potential uses of polymer gel dosimetry when incorporating radioisotopes. The thesis begins by outlining the current status of TRT and the need for accurate dosimetry. The inaccuracies of the dosimetry methods being employed are highlighted, as is the requirement of a "gold standard" method for dosimetry quality assurance. Polymer gel dosimeters are porposed as a possible means of achieving this. As a research topic in its own right an introduction into polymer gel dosimeters is given with a detailed description of their development and current uses in external beam radiotherapy. In the thesis polymer gel dosimeters are used in conjunction with MR and a detailed description of the MR techniques used is also given. Monte Carlo simulations are currently considered the best method to determine absorbed dose from a known activity distribution. A Monte Carlo user code written for EGSnrc has been developed to verify and validate polymer gel dosimetry. Details of the Monte Carlo code are given and comparisons made with published data. The accuracy of poymer gel dosimetry is susceptible to many factors and use with internal isotopes may introduce further technical issues. These are investigated in a number of small experiments and comparison made with external beam irradiation. A method for using polymer gel dosimeters with internal isotopes is developed and verified by comparing dose measurements and distributions with that calculated using the Monte Carlo code. Comparisons with various SPECT based dosimetry techniques have been made for geometrical phantoms of both uniform and non-uniform distributions. Methods for comparing and analysing 3D dose maps have also been investigated and the results from these experiments discussed. The thesis concludes with a case study, whereby polymer gel dosimeters are used for analysis of a specific patient situation. A patient synopsis is given with details of an anatomical phantom based on that patient. Polymer gel and SPECT based dosimetry is performed and the clinical significance of the findings discussed.

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41

Sedaghat, Mahbod. "A study on radiochemical errors in polymer gel dosimeters." Thèse, Université de Sherbrooke, 2012. http://hdl.handle.net/11143/6252.

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À ce jour, les seul dosimètres purement tridimensionnels (3D) sont basés sur la détection d’une propriété physique résultant d’une série de réactions chimiques radio-induites dans un volume de gel ou de plastique. Les études initiales ont généré beaucoup d’enthousiasme mais ces dosimètres 3D ne sont pas parvenus à une utilisation répandue dans les départements de radio-oncologie pour l’assurance-qualité 3D et la vérification de traitements complexes de radiothérapie moderne. Le temps et la complexité de la préparation de ces dosimètres 3D ne sont pas les raisons principales qui empêchent leur déploiement clinique. Ce sont plutôt leurs performances et la reproductibilité des mesures qui doivent être améliorées. Les plus étudiés et les plus utilisés parmi les différents types de dosimètres 3D sont les dosimètres à gels de polymère. De nombreuses compositions chimiques ont été proposées et testées pour la dosimétrie à gels de polymère. L’utilisation d’un antioxydant s’est révélée une découverte majeure dans le domaine puisque l’oxygène interfère avec le mécanisme de réponse des gels. Pourtant, un nombre croissant d’erreurs inexpliquées ont été rapportées dans les écrits et ont soulevé un doute sur la reproductibilité et la justesse des doses déterminées avec ces gels. Cette thèse a été entreprise pour étudier les sources radiochimiques d’erreurs dans les dosimètres à gels de polymère. Il était admis dans les écrits que l’utilisation d’un antioxydant permettait de contoumer tous les effets non-désirés de l’oxygène. Cette thèse démontre que cela était faux. Une méthodologie a été développée pour isoler l’effet de l’oxygène dans un gel de polymère contenant ou non un antioxydant. Les résultats ont révélé que la présence conjointe d’oxygène et d’antioxydant modifie la réponse du dosimètre. Indépendamment de la composition du dosimètre et de l’antioxydant, cet effet peut induire des erreurs dosimétriques significatives dans des mesures simples et dont les origines étaient difficilement appréciables en ignorant l’effet de l'oxygène et de l’antioxydant. Nos résultats nous permettent de postuler les réactions dominantes des antioxydants étudiés et leur devenir chimique au sein d’un gel de polymère sous irradiation. Puisque l’effet de l’oxygène et de l’antioxydant était négligé, plusieurs autres facteurs physico-chimiques faisaient l’objet d’hypothèse pour expliquer les erreurs observées. Ces facteurs incluent la compression des gels et des variations de propagation et de terminaison de la polymérisation reliées à la chaleur générée pendant la polymérisation. Des études détaillées de ces effets nous permettent de refuter ces hypothèses. Nos résultats nous permettent d’analyser, de catégoriser et de proposer des explications sur l’origine des erreurs dosimétriques recensées dans les écrits. Finalement, l’effet d’un antioxydant en particulier, le chlorure de tetrakis-(hydroxyméthyle) phosphonium (THPC), a été étudié en relation avec la structure du polymère formé dans un gel de polymère basé sur l’acrylamide. Le THPC est l’antioxydant le plus utilisé dans les différents dosimètres à gels de polymère. La spectroscopie FT-Raman et la microscopie électronique ont révélé que le THPC réagit avec les monomères pendant la polymérisation. Notre interprétation suggère un rôle important du THPC dans les variations de réponse à la dose dans les gels de polymère. La conclusion générale de cette thèse est que l’élimination chimique de l'oxygène par un antioxydant facilite grandement la préparation des dosimètres mais leur performance en est grandement altérée en comparaison avec des préparations dites anoxiques. L’oxygène demeure une source majeure d’erreur dans les dosimètres à gels de polymère.

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42

Oliveira, Lucas Nonato de. "Parâmetros dosimétricos e coeficiente de difusão para elétrons em campos pequenos, através do dosímetro Fricke Xilenol Gel." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-06062008-173808/.

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A qualidade para o tratamento radioterápico depende essencialmente da capacidade de realizar medidas de dose absorvida no volume de tratamento, minimizando aquela nos tecidos vizinhos, para tal é necessária a determinação dos parâmetros dosimétricos como Porcentagem de Dose Profunda, Perfil de Campo e Fator de Campo que auxiliam a rotina da radioterapia. Os objetivos deste trabalho são: a determinação desses parâmetros para campos pequenos com feixes de elétrons, através dos dosímetro FXG e compará-los com os obtidos com uma câmara de ionização (CI), além de obter o coeficiente de difusão para o dosímetro FXG e sua energia de ativação. Dessa maneira, campos pequenos foram formados através de colimadores especiais dos quais os parâmetros puderam ser inferidos para ambos os dosímetros. O parâmetro dosimétrico Perfil de Campo foi utilizado também para as medidas do coeficiente de difusão, necessário para se corrigir a dose absorvida no tempo, o qual foi analisado através de uma metodologia inovadora das medidas das absorbâncias espaçostemporais e devido aos seus comportamentos comparados a funções gaussianas, o que possibilitou a sua determinação. O FXG apresentou resolução espacial suficiente para a determinação dos parâmetros dosimétricos, os coeficientes de difusão obtidos têm valores respectivos de 0,20 ± 0,03 e 0,40 ± 0,02 mm2/h, e destes a energia de ativação inferida foi de 0,3 ± 0,1 eV. Das análises dos resultados, pode-se concluir que o FXG pode ser utilizado na rotina de radioterapia também para campos pequenos.
Dosimetric parameters such as Percentage Depth Dose, Field Profile and Output Factor are necessary in radiotherapy routine, once they can help to improve the quality of the treatment and consequently of the absorbed dose delivered to the tumor. In this work the dosimetric parameters for electron beams of 8 and 10 MeV were measured with the chemical dosimeter Fricke Xylenol Gel for small field sizes (square and circular) and were compared with those obtained with an ionization chamber. The chemical dosimeter signal, given by the complex Fe+3 - Xylenol concentration, has a temporal dependency, to which its diffusion coefficient was determined together with the activation energy, necessary for the Fe+3 migrations in the gel. These two parameters were measured, for the first time, for the Fricke Xylenol Gel and for that a novel methodology was also created. The measured parameters, dosimetric ones together with the diffusion coefficient and activation energy corroborate, to present the chemical dosimeter, as an adequate one to be used in radiotherapy with electron beams for small field sizes.

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Crescenti, Remo Andrea. "Backscatter ultrasound readout of radiation-sensitive gels for radiation dosimetry." Thesis, Institute of Cancer Research (University Of London), 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.511163.

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Seydaliev, Marat Radikovich. "Development and Test of a GEM-Based TEPC for Neutron Protection Dosimetry." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14607.

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The effective dose equivalent, H (or the effective dose, E ) to an individual is the primary limiting quantity in radiation protection. However, techniques for measuring H for neutrons have not been fully developed. In this regard a new tissue equivalent proportional counter (TEPC) based on a gas electron multiplier (GEM) for measuring H*(10), which is a conservative estimate of H, for neutrons was designed and constructed. The deposited energy distribution for two different neutron sources (a Cf-252 source and a AmBe source) was measured using the new TEPC. The measurements were performed using two different proportional gases: P-10 gas and a propane-based tissue equivalent gas at various pressures. A computer simulation of the new TEPC, based on the Monte Carlo method, was performed in order to obtain the pulse height distributions for the two neutron sources. The simulated results and the measured results were compared. Results show that the experimental results agree with the computational results within 20% of accuracy for both Cf-252 and AmBe neutron sources. A new model GEM-based TEPC was developed for use in obtaining H*(10). The value of H*(10) for the Cf-252 source and for the AmBe source using experimental measurements was obtained. These results are presented in this study. The study shows that the GEM-based TEPC can successfully estimate H*(10). With these results and some refinements, this GEM-based TEPC can directly be used as a neutron rem meter.

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45

Brodeur, Marylène. "Verification of IMRT beam delivery with a ferrous sulfate gel dosimeter and MRI." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=78331.

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Intensity modulated photon beam radiation therapy often results in dynamically delivered beams with small field sizes and steep dose gradients. This defines a need for an integrating, tissue-equivalent, high resolution dosimeter. 3D ferrous sulfate gel based dosimetry involves the use of magnetic resonance (MR) images of radiosensitive paramagnetic gels. The goal of this work is to create a patient specific quality assurance (QA) procedure that links measured dosimetnc information to clinical goals.
The gel dosimeter system is tested through a set of simple experiments which characterize and confirm the system as a valid QA tool for conformal and intensity modulated radiation therapy.
For this work, dynamic photon beams are created on a commercially available inverse treatment planning system and the treatment is delivered to a gel filled acrylic mold. Software has been developed to quantify dose from the QA MR images, and to register this information to the planning computed tomography (CT) scan. The software displays the measured dose on the planning CT, and calculates dose-volume histograms for the registered measured data and contoured patient structures. This work reveals good agreement between planned and measured dose distributions, with less than 5% difference in the mean doses of the contoured patient structures.

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46

Pianoschi, Thatiane Alves. "Estudo de dosimetria gel polimérica em radioterapia com feixes de elétrons utilizando ressonância magnética e simulação Monte Carlo." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-07102014-113550/.

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Radioterapia com feixe de elétrons tem sido empregada, frequentemente, para tratamentos de neoplasias superficiais, devido às características de alcance bem definido e alto gradiente de dose em pouca profundidade. Para que as novas técnicas radioterápicas com esse tipo de feixe possam ser implementadas com segurança é necessária a realização de um controle da qualidade rigoroso. Protocolos recomendam que o controle da qualidade para esse tipo de feixe seja realizado com câmara de ionização, porém dosímetros termoluminescentes, diodos e filmes também são empregados com essa finalidade. Entretanto, esses dosímetros não possuem simultaneamente um conjunto de características essenciais para realização do controle da qualidade, como alta resolução espacial, baixa dependência energética, possibilidade de uso em altos gradientes de dose e distribuição tridimensional de dose. Nesse trabalho avaliou-se a utilização do dosímetro polimérico MAGIC-f gel em aplicações em controle da qualidade em Radioterapia com feixes de elétrons. As leituras das amostras de gel foram realizas por ressonância magnética e simulação Monte Carlo foi utilizada para comparação dos resultados. Como parte de um controle da qualidade para feixe de elétrons, foram determinados parâmetros dosimétricos, como perfil de dose e porcentagem de dose em profundidade, e fatores de qualidade do feixe, como R50, em condições de referência e para campos pequenos. Da comparação entre os dados clínicos e MAGIC-f as diferenças máximas encontradas foram de 4%. Além disso, distribuições de dose de aplicações clínicas com feixes de elétrons foram avaliadas pelo método de comparação do índice gama. Considerando os critérios de 3% e 3 mm, os resultados obtidos para o índice gama mostraram concordâncias acima de 94% para os métodos dosimétricos utilizados. Dessa forma, de acordo com as medidas dosimétricas realizadas com o dosímetro MAGIC-f gel conclui- se que a dosimetria polimérica gel pode ser empregada como uma ferramenta auxiliar em procedimentos de controle da qualidade em Radioterapia com feixes de elétrons, assim como uma ferramenta na determinação das distribuições tridimensionais de dose para feixe de elétrons.
Electron beam radiotherapy has been used frequently for treatments of superficial tumors, due its characteristics of well-defined range and high dose gradient at low depth. For new radiotherapy techniques with this type of beam, a strict quality control is necessary for a safe implementation. Protocols recommend that the quality control for electron beams must be performed with an ionization chamber. However, thermoluminescent dosimeters, films and diodes are also used for this purpose. Although, these dosimeters do not have a set of essential characteristics for performing quality control, like high spatial resolution, low energy dependence, possibility of use in high dose gradients and three dimensional dose distribution acquisition. The present work evaluated the use of MAGIC-f gel dosimeter for the quality control in radiotherapy with electron beams. The readings of the gel samples were made by magnetic resonance imaging and Monte Carlo simulation was used to compare the obtained results. As part of a quality control for the electron beam parameters as percentage depth dose and beam profile were determined. Also beam quality factors, such as R50, were calculated in reference conditions and for small fields. The obtained results were compared with clinical data and MAGIC-f the maximum obtained difference was 4%. In addition, dose distributions from clinical applications with electron beams were evaluated by the gamma index. Considering the criteria of 3% DD and 3 mm DTA, the results showed concordance greater than 94% for all dosimetric methods. Thus, according to the dosimetric measurements through MAGIC-f gel dosimeter it can be inferred that the gel dosimeter can be used as auxiliary tool in the quality control procedures in radiotherapy to electron beam. Also, MAGIC-f is a useful a tool to determine tridimensional dose distributions of electron beam.

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Aranda, Lara Liliana, and García Eugenio Torres. "Modelado de Tejido Biológico con Maniquí de Gel de AGAR por dosimetría del 99mTc." Tesis de Licenciatura, Medicina-Quimica, 2013. http://hdl.handle.net/20.500.11799/14420.

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Moreira, Marcos Vasques. "Dosimetria Fricke Xilenol Gel na região de não-equilíbrio para radioterapia com feixes de fótons e elétrons." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/59/59135/tde-22072013-102348/.

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Quando se utiliza feixes de radiação ionizante de fótons e elétrons com altas energias, a região mais perto da superfície do paciente, região de não-equilíbrio, pode ter o comportamento das doses absorvidas comprometido devido a vários fatores como a presença de materiais auxiliares na radioterapia, exemplo o \"bolus\" (para superficializar a dose absorvida) e materiais imobilizadores como a máscara termoplástica. Dependendo da significância da incerteza no valor da dose absorvida, medidas devem ser tomadas para que esta seja mais próxima possível daquela prescrita. O objetivo desse trabalho é o de avaliar a capacidade do FXG para medidas de dose absorvida na região de não-equilíbrio e o comportamento dessas. Os objetivos específicos foram: (1) o de avaliar e comparar os (µ/?) experimentais e simulados (X-COM e GEANT-4) para diversos materiais, incluindo o FXG, (2) avaliar a influência da máscara termoplástica na dose absorvida prescrita e (3) determinar o ponto de equilíbrio eletrônico, R100, em função das energias dos feixes de fótons e elétrons para diversos materiais. Dos resultados obtidos tem-se que o (µ/?) relativo ao FXG é próximo daquele do tecido mole (TM), o material da máscara influencia a distribuição da dose absorvida na região de não-equilíbrio e os valores obtidos experimentalmente e por simulação MathLab® e PENELOPE® , indicam equivalência entre os materiais da câmara de ionização (CI) e Água, diferentes da equivalência do FXG eTM. Esse último resultado corrobora aquele obtido no experimento para determinação do (µ/?) , levando a concluir a adequabilidade do FXG para medidas na região de não-equilíbrio.
When one uses high energies photons and electrons ionizing radiations beam, the region closer to the surface of the patient, non-equilibrium region, can obtain the absorbed dose behavior compromised due to several factors such as the presence of auxiliary materials in radiotherapy, like the \"bolus\" (used to superficialize the absorbed dose) and immobilizing material as the thermoplastic mask. Depending on the significance of the uncertainty in the dose absorbed value, measurements must be taken in order the measured value be as close as possible to that prescribed. The aim of this paper is to evaluate the ability of FXG for the measurements of the absorbed dose in the region of non-equilibrium and their behavior. The specific object ives are: (1) to evaluate and compare the µ/? experimental and simulated (X-COM and GEANT-4) for various materials, including the FXG; (2) to evaluate the influence of the therm oplastic mask in the prescribed absorbed dose, and (3) to determine the equilibrium electronic point, R100, depending on the photon and electron beam energies for various materials. The results present that the FXG µ/? is close to that of the soft tissue (TM); the mask material influences the absorbed dose distribution in the non-equilibrium region, and the values obtained experimentally and also through MatLab® and Penelope® simulation indicate equivalence between the materials of ionization chamber (IC) a nd water, different from the equivalence between the FXG and TM. This last result corroborates the obtained one in the experiment for the µ/? determination, suggesting the adequacy of FXG for measurements in the non-equilibrium region.

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Afonso, Luciana Caminha. "Estudo da influência de partículas de ouro na dose absorvida em tecido mole utilizando dosimetria com gel polimérico." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/85/85131/tde-21112011-091727/.

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A presença de material de alto número atômico adjacente ao tecido mole aumenta localmente a dose absorvida pelo tecido quando submetido à radiação. Este efeito ocorre devido aos fotoelétrons ejetados do material de alto número atômico. Dosímetros de gel polimérico com partículas de ouro foram utilizados para investigar este efeito. Foram realizados cálculos analíticos para estimar o aumento de dose e simulações com o método de Monte Carlo. A irradiação de amostras de gel polimérico (GP) puro e com 0,005 gAu/gGP utilizando um feixe de raios X produzido por um potencial de 150 kV filtrado com 4 mmAl e 5 mmCu resultou em uma dose absorvida pelas amostras com ouro aproximadamente 20% maior que a dose absorvida pelas amostras de gel polimérico puro. Os cálculos analíticos e a simulação com o método de Monte Carlo resultaram em um aumento de aproximadamente 30% na dose absorvida.
The presence of high-Z material adjacent to soft tissue, when submitted to irradiation, enhances locally the absorbed dose in these soft tissues. Such effect occurs due to the outscattering of photoelectrons from the high-Z material. Polymer gel dosimeters have been used to investigate this effect. Analytic calculations to estimate the dose enhancement and Monte Carlo simulations have been performed. Samples containing polymer gel (PG) with 0.005 gAu/gPG and pure polymer gel have been irradiated using an X-rays beam produced by 150 kV, filtered with 4 mm Al and 5 mm Cu, which resulted in an approximately 20% higher absorbed dose in the samples with gold in comparison to those with pure polymer gel. The analytic calculations and the Monte Carlo simulation resulted in a dose enhancement factor of approximately 30%.

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Dias, Juliana Rosada. "Caracterização dosimétrica de gel tipo VIPARnd através de técnicas ópticas para feixes de raios x de 6mv usados em radioterapia externa." reponame:Repositório Institucional da UnB, 2015. http://repositorio.unb.br/handle/10482/19010.

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Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Elétrica, 2015.
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Neste trabalho as principais características ópticas do dosímetro gel VIPARnd foram avaliadas para feixes de fótons de 6 MV usados em radioterapia externa. O espectro de absorvância do dosímetro gel foi avaliado com espectrofotometria óptica e através do processamento de imagens fotográficas adquiridas com câmera de sensor CMOS para doses de 0 a 50 Gy. Foram avaliadas duas soluções com concentrações diferentes dos componentes do gel. Os dados obtidos através da espectrofotometria óptica mostram que o VIPARnd apresenta pico de absorção entre 300 a 320 nm dependendo da dose absorvida. O aumento da dose absorvida causa aumento na absorvância do VIPARnd. As curvas de dose resposta foram analisadas em função do máximo de absorção e também através da área sob o espectro. A solução 1 apresenta região linear de 3 a 20 Gy e a solução 2 para a região de 0,5 a 5 Gy. A repetitividade entre amostras de um mesmo lote ficou em 0,5% e a reprodutibilidade inter-lotes em 5 %. A estabilidade do gel VIPARnd foi mantida para um tempo pós-irradiação de pelo menos 15 dias. As imagens fotográficas foram adquiridas em escala RGB, a partir da análise de absorção óptica foi suposto que a componente azul apresentasse maior resposta para determinação da dose absorvida o que de fato foi comprovado com os dados obtidos. Para este caso a faixa de resposta linear obtida foi entre 3 e 20 Gy para a solução 1 e entre 0,5 e 20 Gy para a solução 2. Como testes adicionais, foi analisado a curva de dose resposta a partir de imagens de tomografia computadorizada, assim como o estudado da aplicação do gel para medidas de perfil de campos pequenos e PDP para feixes de raios X de 6 MV e a resposta do gel à irradiações com fonte de irídio 192 usadas em braquiterapia de alta taxa de dose. O bom desempenho do dosímetro VIPARnd nos testes realizados indica que este pode ser utilizado na avaliação tridimensional da dose em tratamento radioterápicos. ____________________________________________________________________________________ ABSTRACT
This work aims to evaluate the optical characteristics of a dosimeter VIPARnd for 6 MV photon beam used in radiotherapy. The absorbance spectrum of irradiated gel dosimeter was evaluated with optical spectrophotometer techniques and with CMOS camera readout for dose range of 0 to 50 Gy. Two solutions with different concentration were evaluated. Data shows that the VIPARnd has a maximum absorbance at 300 to 320 nm depending on the absorbed dose. The absorbed dose increases the absorbance values of VIPARnd. The dose response curves were obtained by the peak value and the relative area under of absorbance curve. The solution 1 shown interval of linearity from 3 to 20 Gy and the solution 2 from 0,5 to 5 Gy. The repeatability and inter-batch reproducibility of gel response were 0,5 % and 5% respectively. Temporal analysis indicates that the gel dosimeter has no significant variation in absorbance peak for the post irradiation times until 15 days. The CMOS camera readouts were obtained in RGB color, the absorbance measurements suggest a major response of dose for blue matrix verified with data. The dose response curve for blue component showed interval of linearity from 3 to 20 Gy for solution 1 and from 0,5 to 20 Gy. Additional tests were performed to determine the dose response with X-ray computed tomography, analyses of dose profile measurements for small field radiation therapy and percentage depth dose for 6 MV photon beam and gel response for irradiation with Iridium 192 source in high dose rate brachytherapy. These characteristics indicate that the presented VIPARnd polymer gel could be helpful for radiotherapy dosimetry.

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