Dissertations / Theses: 'Distributions de dose'

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Öström, Linn. "Post-processingof Monte Carlo calculated dose distributions." Thesis, KTH, Matematisk statistik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-244314.

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This Master Thesis focuses on denoising of Monte Carlo calculated dose distributions of radiosurgery treatment plans. The objective of this project is to implement a Denoising Autoencoder (DAE) and investigate its denoising performance when it has been trained on Monte Carlo calculated dose distributions generated with lower number of photon showers. The DAE is trained in a supervised setting to learn the mapping between corrupted observations and clean ones. The questions this thesis aims to answer are: (i) Can a DAE be used to denoise Monte Carlo calculated dose distributions, and thus predict the dose prior to a full simulation? Additionally, (ii) does incorporating prior knowledge of shot position increase the denoising performance? The results in this investigation have shown that the network successfully predicts the dose for low number of photon showers. In very heavy noise inputs the network denoising was in general successful, and the network could fill in missing data. The results indicated that the DAE could reduce the level of noise with an amount comparable with simulations that were done with 102 times more samples.
Denna masteruppsats fokus är på att brusreducera Monte Carlo-beräknade dosdis-tributioner för behandlingsplaner i hjärnstereotaktisk radiokirurgi. Projektets avsikt är att implementera en brusreducerande Autoencoder (DAE) samt undersöka dess brusreducerande egenskaper, när nätverket har tränats på Monte Carlo-beräknade dosdistributioner genererade med få fotonsimulationer. Den brusreducerande Au-toencodern har genomgått övervakad träning, där den lär sig en avbildning mellan brusiga till brusfria distributioner. Frågorna som denna uppsats ämnar besvara är;(i) Kan en brusreducerande Autoencoder användas för att brusreducera Monte Carlo-beräknade dosdistributioner, och därmed förutspå dosen på förhand? Dessutom, (ii) förbättras nätverkets brusreducerande prestanda när ytterligare information angående skottpositionerna tillförs till nätverket? Resultaten i denna undersökning pekade på att nätverket framgångsrikt förutspår dosdistributionerna, baserat på dosdistribu-tioner som simulerats med få fotonsimulationer. I de fall då bruset i indata är väldigt kraftigt lyckas fortfarande nätverket att brusreducera, samt lyckat fylla i data som saknas. Resultaten indikerade att den brusreducerande Autoencodern kunde reduc-era brus i en mängd som kan jämföras med en simulation som gjorts med en faktor 102 fler fotonsimulationer.

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Milette, Marie-Pierre. "Direct optimization of 3D dose distributions using collimator rotation." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/274.

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The primary goal of this thesis is to improve the precision and efficiency of radiation therapy treatment. This goal is achieved by developing and implementing a direct aperture optimization (DAO) platform where the multileaf collimator (MLC) is rotated between each aperture. The approach is referred to as rotating aperture optimization (RAO). A series of tests is performed to evaluate how a final optimized plan depends on MLC parameters. Imposing constraints on the leaf sequence results in increased efficiency and a simplification of the treatment plan without compromising the quality of the dose distribution. It is also shown that an arrangement of equispaced collimator angles takes full advantage of the flexibility associated with collimator rotation. A study including ten recurring nasopharynx cancer patients is used to evaluate the capabilities of RAO compared to other optimization techniques. It is shown that RAO plans require significantly less linac radiation output (monitor units or MU) while maintaining equivalent dose distribution quality compared to plans generated with the conventional fluence based approach. Furthermore with an improved collimator rotation speed, the RAO plans should be executable in the same or less time than plans generated with the fluence-based approach. For the second part of the study it is shown that plans generated with RAO are as good as or better than plans generated with standard fixed collimator DAO. Film and ion chamber measurements indicate that RAO plans can be delivered more accurately than DAO plans. Additional applications of DAO were investigated through collaboration with two PhD students. First, Monte Carlo was used to generate pencil beam dose distributions for DAO inverse treatment planning (MC-DAO). The MC-DAO technique correctly models traditionally difficult treatment geometries such as small fields and tissue inhomogeneities. The MC-DAO also takes advantage of the improved MU efficiency associated with the DAO technique. Secondly DAO is proposed for adaptive radiation therapy. The results show that plan re-adaptation can be performed more quickly than complete plan regeneration thereby minimizing the time the patient has to spend in the treatment room and reducing the potential for geometric errors in treatment delivery.

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Nilsson, Viktor. "Prediction of Dose Probability Distributions Using Mixture Density Networks." Thesis, KTH, Matematisk statistik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-273610.

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In recent years, machine learning has become utilized in external radiation therapy treatment planning. This involves automatic generation of treatment plans based on CT-scans and other spatial information such as the location of tumors and organs. The utility lies in relieving clinical staff from the labor of manually or semi-manually creating such plans. Rather than predicting a deterministic plan, there is great value in modeling it stochastically, i.e. predicting a probability distribution of dose from CT-scans and delineated biological structures. The stochasticity inherent in the RT treatment problem stems from the fact that a range of different plans can be adequate for a patient. The particular distribution can be thought of as the prevalence in preferences among clinicians. Having more information about the range of possible plans represented in one model entails that there is more flexibility in forming a final plan. Additionally, the model will be able to reflect the potentially conflicting clinical trade-offs; these will occur as multimodal distributions of dose in areas where there is a high variance. At RaySearch, the current method for doing this uses probabilistic random forests, an augmentation of the classical random forest algorithm. A current direction of research is learning the probability distribution using deep learning. A novel parametric approach to this is letting a suitable deep neural network approximate the parameters of a Gaussian mixture model in each volume element. Such a neural network is known as a mixture density network. This thesis establishes theoretical results of artificial neural networks, mainly the universal approximation theorem, applied to the activation functions used in the thesis. It will then proceed to investigate the power of deep learning in predicting dose distributions, both deterministically and stochastically. The primary objective is to investigate the feasibility of mixture density networks for stochastic prediction. The research question is the following. U-nets and Mixture Density Networks will be combined to predict stochastic doses. Does there exist such a network, powerful enough to detect and model bimodality? The experiments and investigations performed in this thesis demonstrate that there is indeed such a network.
Under de senaste åren har maskininlärning börjat nyttjas i extern strålbehandlingsplanering. Detta involverar automatisk generering av behandlingsplaner baserade på datortomografibilder och annan rumslig information, såsom placering av tumörer och organ. Nyttan ligger i att avlasta klinisk personal från arbetet med manuellt eller halvmanuellt skapa sådana planer. I stället för att predicera en deterministisk plan finns det stort värde att modellera den stokastiskt, det vill säga predicera en sannolikhetsfördelning av dos utifrån datortomografibilder och konturerade biologiska strukturer. Stokasticiteten som förekommer i strålterapibehandlingsproblemet beror på att en rad olika planer kan vara adekvata för en patient. Den särskilda fördelningen kan betraktas som förekomsten av preferenser bland klinisk personal. Att ha mer information om utbudet av möjliga planer representerat i en modell innebär att det finns mer flexibilitet i utformningen av en slutlig plan. Dessutom kommer modellen att kunna återspegla de potentiellt motstridiga kliniska avvägningarna; dessa kommer påträffas som multimodala fördelningar av dosen i områden där det finns en hög varians. På RaySearch används en probabilistisk random forest för att skapa dessa fördelningar, denna metod är en utökning av den klassiska random forest-algoritmen. En aktuell forskningsriktning är att generera in sannolikhetsfördelningen med hjälp av djupinlärning. Ett oprövat parametriskt tillvägagångssätt för detta är att låta ett lämpligt djupt neuralt nätverk approximera parametrarna för en Gaussisk mixturmodell i varje volymelement. Ett sådant neuralt nätverk är känt som ett mixturdensitetsnätverk. Den här uppsatsen fastställer teoretiska resultat för artificiella neurala nätverk, främst det universella approximationsteoremet, tillämpat på de aktiveringsfunktioner som används i uppsatsen. Den fortsätter sedan att utforska styrkan av djupinlärning i att predicera dosfördelningar, både deterministiskt och stokastiskt. Det primära målet är att undersöka lämpligheten av mixturdensitetsnätverk för stokastisk prediktion. Forskningsfrågan är följande. U-nets och mixturdensitetsnätverk kommer att kombineras för att predicera stokastiska doser. Finns det ett sådant nätverk som är tillräckligt kraftfullt för att upptäcka och modellera bimodalitet? Experimenten och undersökningarna som utförts i denna uppsats visar att det faktiskt finns ett sådant nätverk.

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Tozer-Loft, Stephen M. "Dose volume analysis in brachytherapy and stereotactic radiosurgery." Thesis, University of Sheffield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366100.

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Fox, Timothy Harold. "Computation and optimization of dose distributions for rotational stereotactic radiosurgery." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/32843.

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South, Christopher Peter. "The use of functional imaging to design optimal radiotherapy dose distributions." Thesis, Institute of Cancer Research (University Of London), 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.538528.

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CECILIO, PAULO J. "Implementacao e aceite de sistema de radioterapia de feixe modulado dinamico com o uso de colimador secundario de multiplas folhas." reponame:Repositório Institucional do IPEN, 2008. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11757.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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Rowbottom, Carl Graham. "Optimisation of beam-orientations in conformal radiotherapy treatment planning." Thesis, Institute of Cancer Research (University Of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314088.

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9

Doucet, Robert. "Experimental verification of Monte Carlo calculated dose distributions for clinical electron beams." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=33750.

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Current electron beam treatment planning algorithms are inadequate to calculate dose distributions in heterogeneous phantoms. Fast Monte Carlo algorithms are accurate in general but their clinical implementation needs validation. Calculations of electron beam dose distributions performed using the fast Monte Carlo system XVMC and the well-benchmarked general-purpose Monte Carlo code EGSnrc were compared with measurements. Irradiations were performed using the 9 MeV and 15 MeV beams from the Clinac 18 accelerator with standard conditions. Percent depth doses and lateral profiles were measured with thermoluminescent dosimeter and electron diode respectively. The accelerator was modelled using EGS4/BEAM, and using an experiment-based beam model. All measurements were corrected by EGSnrc calculated stopping power ratios. Overall, the agreement between measurement and calculation is excellent. Small remaining discrepancies can be attributed to the non-equivalence between physical and simulated lung material, precision in energy tuning, beam model parameters optimisation and detector fluence perturbation effects.

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Hellström, Terese. "Deep-learning based prediction model for dose distributions in lung cancer patients." Thesis, Stockholms universitet, Fysikum, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-196891.

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Background To combat one of the leading causes of death worldwide, lung cancer treatment techniques and modalities are advancing, and the treatment options are becoming increasingly individualized. Modern cancer treatment includes the option for the patient to be treated with proton therapy, which can in some cases spare healthy tissue from excessive dose better than conventional photon radiotherapy. However, to assess the benefit of proton therapy compared to photon therapy, it is necessary to make both treatment plans to get information about the Tumour Control Probability (TCP) and the Normal Tissue Complication Probability (NTCP). This requires excessive treatment planning time and increases the workload for planners. Aim This project aims to investigate the possibility for automated prediction of the treatment dose distribution using a deep learning network for lung cancer patients treated with photon radiotherapy. This is an initial step towards decreasing the overall planning time and would allow for efficient estimation of the NTCP for each treatment plan and lower the workload of treatment planning technicians. The purpose of the current work was also to understand which features of the input data and training specifics were essential for producing accurate predictions. Methods Three different deep learning networks were developed to assess the difference in performance based on the complexity of the input for the network. The deep learning models were applied for predictions of the dose distribution of lung cancer treatment and used data from 95 patient treatments. The networks were trained with a U-net architecture using input data from the planning Computed Tomography (CT) and volume contours to produce an output of the dose distribution of the same image size. The network performance was evaluated based on the error of the predicted mean dose to Organs At Risk (OAR) as well as the shape of the predicted Dose-Volume Histogram (DVH) and individual dose distributions. Results The optimal input combination was the CT scan and lung, mediastinum envelope and Planning Target Volume (PTV) contours. The model predictions showed a homogenous dose distribution over the PTV with a steep fall-off seen in the DVH. However, the dose distributions had a blurred appearance and the predictions of the doses to the OARs were therefore not as accurate as of the doses to the PTV compared to the manual treatment plans. The performance of the network trained with the Houndsfield Unit input of the CT scan had similar performance as the network trained without it. Conclusions As one of the novel attempts to assess the potential for a deep learning-based prediction model for the dose distribution based on minimal input, this study shows promising results. To develop this kind of model further a larger data set would be needed and the training method could be expanded as a generative adversarial network or as a more developed U-net network.

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Robar, James L. "Film dosimetry and three-dimensional verification of conformal dose distributions in stereotactic radiosurgery." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0019/NQ48701.pdf.

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12

Gillespie, Timothy James. "A computer model of beta particle dose distributions in lithium fluoride and tissue." Thesis, Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/16952.

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13

Fragoso, Margarida. "Application of Monte Carlo techniques for the calculation of accurate brachytherapy dose distributions." Thesis, Institute of Cancer Research (University Of London), 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413609.

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14

Bero, Mamdouh A. "Development of a three-dimensional radiation dosimetry system." Thesis, University of Surrey, 2001. http://epubs.surrey.ac.uk/719/.

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SCAFF, LUIZ A. M. "Metodo de calculo de dose na irradiacao de todo o corpo com raios gama do cobalto-60." reponame:Repositório Institucional do IPEN, 2001. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10901.

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Tese (Doutaramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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MADUAR, MARCELO F. "Determinacao de fatores de conversao de dose para radiacao gama externa em residencias." reponame:Repositório Institucional do IPEN, 2000. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10816.

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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Belanger, Philippe. "MR based frickle-gelatin dosimetry : uncertainty evaluation and computerised analysis of measured dose distributions." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=32759.

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Dynamically delivered intensity modulated beams (IMBs) pose unique verification problems that may be addressed with the use of integrating continuous 3D dosimeters such as gel based Fricke dosimeters. Accurate knowledge of the ability of these dosimeters to measure adequately and precisely the delivered dose is a prerequisite for their clinical use. The magnetic properties of the ferrous and ferric ions present in the gel based Fricke dosimeter after its irradiation are the basis for the use of magnetic resonance imaging (MRI) in the measurement of dose. This thesis presents the investigation of a 3D gel based Fricke dosimetry system (Fricke-gel). A software system is developed and spin-lattice relaxation rate (R1) images are computed from MR images of irradiated Fricke-gel phantoms in order to quantify the dosimetric uncertainties resulting from the MR imaging system, from the gel itself, as well as from the external parameters. The sensitivity and the minimum detectable dose of the Fricke-gel dosimeter are determined. Validation of the dosimeter's capacity to measure dose distributions is made through measurement of percent depth dose curves (PDD's), and field profiles (open and wedged). An example of clinical utilisation of the Fricke-gel dosimeter is presented. Dose distributions are evaluated visually by 3D software tools and quantitatively analyzed by dose-volume histograms. Results show a good correlation between the Fricke-gel measured dose distributions and treatment planning software dose calculations.

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Nilsson, Kenneth A. "Simulating Accidental Exposures to deliberate Intrusions in Pipe Networks." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1091122400.

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Popov, G. F., S. I. Savan, R. V. Lazurik, and A. V. Pochynok. "Selection of calculation methods for the analysis of absorbed depth-dose distributions of electron beams." Thesis, Sumy State University, 2016. http://essuir.sumdu.edu.ua/handle/123456789/46936.

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The work is dedicated to comparison methods of processing the results of measurements of the absorbed depth-dose distributions (DDD) of the electron radiation to determine the practical range of electrons. The sets of test data were obtained by modeling the DDD with use Monte Carlo method. The accuracy of the calculation method is determined by the mean square error of processing results the sets of test data. In the paper it was performed the comparison of computational methods of processing the measurement results that differs in the sizes of the array of data being processed and types of functions which use for approximation the data. Comparison the accuracy methods is base for the recommendations on the selection of computational methods for determining the practical range of electrons for computational dosimetry of electron radiation.

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Dybwad, Anniken. "Comparison of Dose Distributions resulting from IMRT and VMAT, and Assessment of MLC Leaf Positioning Errors." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-22432.

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Intensity-modulated radiotherapy (IMRT) is a radiation technique used in the treatment of head-and-neck cancer patients. IMRT results in a dose distribution which conforms to the tumor volume(s), and therefore sparing surrounding normal tissue. However, the radiation delivery is relatively time consuming. Volumetric modulated arc therapy (VMAT) on the other hand, has a radiation delivery time down to one third compared to that of IMRT (depending on number of arcs, arc lengths etc.). This shortened treatment time will allow more treatments per day, and a decrease in discomfort which may be experienced by the patients undergoing radiotherapy. Due to the differences in radiation delivery time, it is of interest to compare the dose distributions resulting from IMRT and VMAT radiation treatment plans.In this study, ten head-and-neck cancer patient cases were used to compare the modalities step-and-shoot IMRT, single-arc VMAT, dual-arc VMAT (two arcs of 356$^\circ$ each) and short dual-arc VMAT (two arcs of 270$^\circ$ each). The Delta4 phantom from ScandiDos was used to measure the resulting dose distributions from each of the 40 radiation treatment plans (4 modalities, 10 patient cases). Each measured dose distribution was then compared with its corresponding calculated phantom dose distribution, which was obtained in Oncentra MasterPlan (treatment planning system) by using artificial CT-images representing the phantom's composition and dimensions.The gamma index was used as the comparison parameter, and the percentage of gamma index values which were $\leq$1 defined the agreement between a measured and calculated dose distribution. The gamma index criteria were set to allow max dose deviation and max spatial deviation of $\pm$3,0$\%$ and $\pm$3,0~mm respectively, and the deviations were normalized to local dose.In order to further compare the radiation modalities, different dose parameters were retrieved from the calculated patient dose distributions resulting from each of the four modalities. The parameters which were assessed were mean dose to parotis, maximum dose to medulla spinalis, homogeneity index for certain treatment volumes (PTVs), and Jaccard index (conformity index) for all treatment volumes combined. The radiation delivery time was also measured for each treatment modality used in this study.In the second part of this study, two systematic MLC leaf positioning errors (MLCpe) were introduced to the treatment plans single-arc VMAT, dual-arc VMAT (two arcs of 356$^\circ$ each) and IMRT of all ten patient cases. The two error-types consisted of 1) a +1~mm shifting of each MLC leaf (opening of aperture), and 2) a -1~mm shifting of each MLC leaf (closing of aperture). The dose distributions resulting from the MLCpe treatment plans, as well as the error-free plans, were measured using the Delta4 phantom. The effects of the errors were evaluated by calculating the relative deviation in mean, minimum and maximum dose within certain chosen volumes.The obtained percentages of gamma index values $\leq$1, show that the accordance between measured and calculated dose distributions was best for the modality IMRT. However, all four treatment modalities had percentages satisfying the pass/fail criteria used at the Department of Radiotherapy (St.\ Olav's Hospital). In terms of the dose parameters which were retrieved from the calculated patient dose distributions, the largest differences between modalities were seen in radiation delivery time and homogeneity index. The three VMAT modalities had markedly shorter radiation delivery times compared to IMRT. The homogeneity indexes, which were calculated for two chosen treatment volumes (PTVs), indicate that the modalities dual-arc and short dual-arc result in best homogeneity for the two volumes, whereas IMRT results in the poorest.The relative deviations in various dose parameters, due to systematic MLC leaf positioning errors (MLCpe), indicate that the VMAT modalities single-arc and dual-arc are generally more affected by systematic MLCpe compared to IMRT. However, for all three evaluated modalities, unwanted clinical effects due to systematic MLCpe may occur for all assessed volumes, due to relatively large deviation percentages.

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Aydarous, Abdulkadir Sheikh. "Development of imaging techniques for determining dose distributions around discrete radioactive particles found in the environment." Thesis, University of Birmingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415424.

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GONCALVES, VINICIUS D. "Caracterização da dose em pacientes devido a produção de imagem de raios-X utilizadas em radioterapia guiada por imagem - IGRT." reponame:Repositório Institucional do IPEN, 2014. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10555.

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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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Beauvais, March Hélène. "Modelisation des distributions de dose sur l'axe pour les faisceaux de photons de haute energie utilises en radiotherapie." Toulouse 3, 1987. http://www.theses.fr/1987TOU30074.

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Faria, Clara Maria Gonçalves de. "Distribuições de limiar de dose e suas causas e consequências em Terapia Fotodinâmica." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-18052017-083829/.

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O princípio de terapia fotodinâmica (TFD) foi introduzido por volta de 1900 mas posteriormente investgado como candidato para tratamento de cancer na década de 1970. Desde então, existem diversos trabalhos a respeito do assunto in vitro, in vivo e em estudos clínicos e grandes avanços foram alcançados. Entretanto, alguns desafios ainda não foram superados, como a variabilidade dos resultados. Este trabalho consiste na investigação de suas causas, em que o principal objetivo é avançar o estado da arte em TFD. Para isso foi usado um modelo de distribuição de limiar de dose para avaliar resistência em TFD in vitro. As distribuições de limiar de dose são obtidas pela derivação a curva de dose resposta experimental. Elas são caracterizadas pela sua largura e pela dose que corresponde ao pico, que se relaciona a homogeneidade e resistência intrínseca da população, respectivamente. Na seção 1, é apresentada a avaliação e comparação de dados obtidos de resultados publicados na literatura e, na seção 2, de experimentos realizados pela autora em diferentes linhagens celulares. Da análise da primeira etapa, foi observado que a largura da distribuição é proporcional a dose do pico e foi possível investigar a dependência do resultado da TFD com a linhagem celular, dado um fotossensibilizador (FS). Foi interessante, também, notar que as distribuições de limiar de dose correspondem a curvas de atividade de marcadores celulares de apoptose, como função da dose de luz, para a maior parte das condições analisadas. Dos experimentos realizados pela autora, foi visto que as células normais são as mais resistentes ao dano, seguida das células de câncer resistentes e sua linhagem parental, e que sua resposta foi a mais homogênea. Essas observações foram corroboradas pelas imagens obtidas de microscopia de fluorescência para avaliação da captação de FS, que mostraram que as células tumorais acumulam mais FS que as outras. Portanto, foi mostrado o potencial de se aplicar distribuições de limiar de dose na análise de resultados de TFD in vitro, ela é uma poderosa ferramenta que fornece mais informações que as curvas de dose resposta padrão.
The principle of photodynamic therapy (PDT) was introduced around 1900 but further investigated as a candidate to cancer treatment in the 1970´s. Since then, there are several papers regarding the subject in vitro, in vivo and clinical trials and great advances were achieved. However, some challenges were not yet overcome, such as results variability. This work consists in the investigation of its causes, where the main goal is to advance the state of art of PDT. For that it is being used a threshold dose distribution model to evaluate cell resistance to PDT in vitro. The threshold distributions are obtained by differentiating the experimental dose response curve. They are characterized by its width and the dose that corresponds to the peak which relates to the homogeneity and intrinsic resistance of the population, respectively. In section 1, it is presented the evaluation and comparison of data obtained from published results in literature and, in section 2, of experiments performed by the author in different cell lines. From the analysis in the first part, it was observed that the width of the distribution is proportional to its dose of the peak and it was possible to investigate the dependence of the PDT result with the cell line, given a fixed photosensitizer (PS). It was also interesting to note that the threshold distribution corresponded to the activity curves for apoptotic cell markers as a function of light dose, for most of the conditions analyzed. From the experiments performed by the author, it was seen that the normal cell line was the most resistant one, followed by the resistant cancer cells and its parental cell line, and that its response was more homogeneous. Those finding were supported by the fluorescence microscopy images obtained to evaluate PS uptake, which shown that the tumor cells accumulated more PS than the other ones. Therefore, it was shown the potential of applying the threshold distribution to analyze PDT results in vitro, it is a powerful tool that provides more information than the standard dose response curves.

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SILVA, ROSIANE A. da. "Dosimetria de filtros dinamicos aprimorados." reponame:Repositório Institucional do IPEN, 2006. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11368.

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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ANGELOCCI, LUCAS V. "Estudo de casos clínicos em radioterapia através do sistema de planejamento AMIGOBrachy." reponame:Repositório Institucional do IPEN, 2016. http://repositorio.ipen.br:8080/xmlui/handle/123456789/26926.

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O sucesso de uma radioterapia depende do correto planejamento da dose a ser entregue ao volume alvo. Na braquiterapia, modalidade da radioterapia onde um radioisótopo selado é implantado intracavitariamente ou intersticialmente no paciente, há menos avanços em sistemas de planejamento de tratamento computacionais do que na teleterapia, amplamente mais utilizada nos serviços típicos. Porém, a braquiterapia, quando aplicável, é preferível por poupar tecidos sadios vizinhos de uma dose desnecessária. O AMIGOBrachy, um sistema de planejamento para braquiterapia de interface amigável, compatibilidade com outros sistemas comerciais em uso e integrado ao código MCNP6 (Monte Carlo N-Particle Transport Code v. 6) foi desenvolvido no Centro de Engenharia Nuclear do Instituto de Pesquisas Energéticas e Nucleares (CEN-IPEN) e atualmente está em processo de validação. Este trabalho contribuiu para este processo, avaliando três diferentes casos clínicos através do AMIGOBrachy com o formalismo do TG43 da AAPM (Associação Americana de Física Médica), protocolo que rege a dosimetria em braquiterapia, e comparando seus resultados com as distribuições de dose calculadas por outros sistemas comerciais consagrados: Varian BrachyVision TM (Varian Medical Systems; Palo Alto, CA, EUA) e Nucletron Oncentra® (Elekta; Estocolmo, Suécia). Os resultados obtidos estão dentro de uma faixa de concordância de ±10%, estando mais discrepantes em regiões muito próximas do aplicador, onde os sistemas de planejamento comerciais e o AMIGOBrachy divergem devido aos diferentes métodos de cálculo. Em pelo menos dois terços da região de interesse, porém, a dose concordou em uma faixa de ±3% para os três casos. Também foram realizadas simulações utilizando o formalismo do TG186 da AAPM, que considera heterogeneidades no tecido, para avaliar o impacto dos mesmos na dose. Em adição ao processo de validação, também foi realizado um estudo em braquiterapia oftálmica para posterior inserção de um módulo adicional ao AMIGOBrachy; para isso, um modelo de olho humano foi desenvolvido utilizando geometria UM (Unstructured Mesh), para validação com o código MCNP6, que apenas nesta versão demonstra um novo recurso capaz de simular uma geometria híbrida: parcialmente analítica, parcialmente UM. O modelo considera dez diferentes estruturas no olho humano: esclera, coroide, retina, corpo vítreo, córnea, câmara anterior, lente, nervo óptico, parede do nervo óptico, e um tumor definido de forma arbitrária crescendo da superfície externa do globo ocular em direção ao seu centro. Os resultados foram comparados com um modelo de olho puramente analítico modelado com o MCNP6 e tomado como referência. Os resultados foram satisfatórios em todas as simulações desenvolvidas, exceto para as estruturas do nervo óptico e sua parede, que devido ao seu pequeno tamanho e distância da fonte, mostraram erros relativos maiores, mas ainda menores que 10%, e não representam problema de preocupação clínica uma vez que recebem doses muito pequenas. Discutiu-se também a eficácia e problemas encontrados nessa nova capacidade do código MCNP de simular geometrias híbridas, uma vez que é recente e ainda apresenta deficiências, que tiveram que ser contornadas no presente trabalho.
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

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Bergman, Alanah Mary. "Monte Carlo simulation of x-ray dose distributions for direct aperture optimization of intensity modulated treatment fields." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/30720.

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This thesis investigates methods of reducing radiation dose calculation errors as applied to a specialized x-ray therapy called intensity modulated radiation therapy (IMRT). There are three major areas of investigation. First, limits of the popular 2D pencil beam kernel (PBK) dose calculation algorithm are explored. The ability to resolve high dose gradients is partly related to the shape of the PBK. Improvements to the spatial resolution can be achieved by modifying the dose kernel shapes already present in the clinical treatment planning system. Optimization of the PBK shape based on measured-to-calculated test pattern dose comparisons reduces the impact of some limitations of this algorithm. However, other limitations remain (e.g. assuming spatial invariance, no modeling of extra-focal radiation, and no modeling of lateral electron transport). These limitations directed this thesis towards the second major investigation - Monte Carlo (MC) simulation for IMRT. MC is considered to be the "gold standard" for radiation dose calculation accuracy. This investigation incorporates MC calculated beamlets of dose deposition into a direct aperture optimization (DAO) algorithm for IMRT inverse planning (MC-DAO) . The goal is to show that accurate tissue inhomogeneity information and lateral electronic transport information, combined with DAO, will improve the quality/accuracy of the patient treatment plan. MC simulation generates accurate beamlet dose distributions in traditionally difficultto- calculate regions (e.g. air-tissue interfaces or small (≤ 5 cm² ) x-ray fields). Combining DAO with MC beamlets reduces the required number of radiation units delivered by the linear accelerator by ~30-50%. The MC method is criticized for having long simulation times (hours). This can be addressed with distributed computing methods and data filtering ('denoising'). The third major investigation describes a practical implementation of the 3D Savitzky-Golay digital filter for MC dose 'denoising'. This thesis concludes that MC-based DAO for IMRT inverse planning is clinically feasible and offers accurate modeling of particle transport and dose deposition in difficult environments where lateral electronic dis-equilibrium exists.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

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Rae, William Ian Duncombe. "Measured dose distributions of iodine-125 sources and the computerised optimisation of their positions in brachytherapy planning." Master's thesis, University of Cape Town, 1987. http://hdl.handle.net/11427/12732.

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Includes bibliographies.
The use of 1-125 seeds in brachytherapy is widespread and becoming increasingly varied. The spatial dose distributions around two types of 1-125 seeds in general use, were measured using a Geiger-Muller chamber. Seeds with the 1-125 adsorbed onto resin spheres had a 10% less anisotropic dose distribution than seeds containing a silver wire with the 1-125 adsorbed onto it. An interpolative method was developed for fast dose calculations taking this anisotropy into account.

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Ermeneux, Louis. "Dosimétrie des systèmes IRM-LINAC utilisés en radiothérapie externe : caractérisation des faisceaux et évaluation des distributions de dose." Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASP005.

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L'IRM-LINAC est un appareil de radiothérapie guidée par l'imagerie combinant un accélérateur linéaire (LINAC) et un imageur par résonance magnétique (IRM), permettant un meilleur suivi de la tumeur. Des problématiques dosimétriques, associées à la présence du champ magnétique statique, ont été soulevées dans la littérature. L'objectif de la thèse est de développer des outils dosimétriques et des protocoles robustes utilisables sur les IRM-LINAC afin d'améliorer la connaissance des doses délivrées aux patients traités avec ces appareils. La première partie du travail se concentre sur la détermination des facteurs d'ouverture du collimateur (FOC) en petits champs sur cet appareil et sur l'étude de la réponse des détecteurs. Comme aucune variation significative de réponse n'a été observée pour des films EBT3 exposés à différentes durées en présence du champ magnétique (0,35 T), ce détecteur 2D à haute résolution a été utilisé pour réaliser plusieurs séries de mesures de FOC sur un IRM-LINAC MRidian qui ont ensuite été comparées aux mesures par détecteurs actifs (chambres d'ionisation, diodes, microdiamant) ainsi qu'aux données du TPS. Un bon accord est observé entre les FOC mesurés et ceux calculés par le TPS pour les tailles de champ supérieures ou égales à 2,5x2,5 cm², une sous-estimation du FOC TPS est observée pour les tailles de champ inférieures (champ 0,83x0,83 cm² : 6% pour les films, et 4% en moyenne pour les détecteurs actifs solides). Après application des facteurs correctifs du TRS483, les mesures par détecteurs actifs convergent vers celles obtenues avec les films. Ces écarts avec le TPS tendent à suggérer la nécessité d'un ajustement plus robuste de l'algorithme du TPS pour les petits champs. Les mesures sont complétées par des simulations Monte-Carlo réalisées avec le code Geant4 pour établir des facteurs correctifs en présence d'un champ magnétique pour les détecteurs actifs. La seconde partie porte sur la faisabilité de lecture par IRM de gels dosimétriques TruView (ModusQA), fabriqués au laboratoire, pour évaluer des distributions de dose. Ces gels caractérisés par lecture IRM (mesure du temps de relaxation T2), ont montré une linéarité de la réponse en dose jusqu'à 7 Gy ainsi qu'une sensibilité faible comparativement à la littérature. Une sensibilité thermique importante et une inhomogénéité du gel entre la surface du gel et le gel situé plus en profondeur ont été observées pour des gels non-irradiés, et des protocoles ont été mis en place pour s'en affranchir. La faisabilité d'utilisation de gels dosimétriques pour la réalisation de contrôle qualité patient sur l'IRM-Linac a été démontrée, une amélioration de la sensibilité du gel est nécessaire afin d'obtenir une dosimétrie fiable avec ce protocole
MR-LINAC are radiotherapy devices that combine a linear accelerator (LINAC) and a magnetic resonance imager (MRI), allowing an improved tumor tracking. Dosimetric issues associated with the presence of the static magnetic field have been discussed in the literature. The aim of this thesis is to develop dosimetric tools and robust protocols for use on MRI-LINACs to enhance the knowledge of the doses delivered to patients treated with these devices. The first part of the work focuses on determining output factors (OF) in small fields on this device and studying detectors' responses. No significant variation in response was observed for EBT3 films exposed to different durations in the presence of the magnetic field (0.35 T). This high-resolution 2D detector was then used to perform several series of OF measurements on an MRidian MR-LINAC, which were then compared with measurements using active detectors (ionization chambers, diodes, microdiamond) as well as with data from the treatment planning system (TPS). A good agreement was observed between the measured OF and those calculated by the TPS for field sizes larger than or equal to 2.5x2.5 cm²; an underestimation of the TPS OF was observed for smaller field sizes (0.83x0.83 cm²: 6% for films and f 4% on average for solid active detectors). After applying TRS483 correction factors, measurements with active detectors converge with those obtained with films. These discrepancies with the TPS suggest the need for a more robust adjustment of the TPS algorithm for small fields. Measurements were complemented by Monte Carlo simulations using the Geant4 code to establish correction factors in the presence of a magnetic field for active detectors. The second part focuses on the feasibility of MRI reading of TruView dosimetric gels (ModusQA) manufactured in the laboratory to evaluate dose distributions. These gels, characterized by MRI reading (measuring T2 relaxation time), exhibited a dose-response linearity up to 7 Gy, along with relatively low sensitivity compared to the literature. Significant thermal sensitivity and gel inhomogeneity between the gel surface and deeper layers were observed in non-irradiated gels, and protocols were implemented to address these issues. The feasibility of using dosimetric gels for patient quality control in MR-Linac has been demonstrated, but an enhancement of gel sensitivity is required to achieve reliable dosimetry with this protocol

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CAVINATO, CHRISTIANNE C. "Padronizacao do metodo de dosimetria fricke gel e avaliacao tridimensional de dose empregando a tecnica de imageamento por ressonancia magnetica." reponame:Repositório Institucional do IPEN, 2009. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9406.

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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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MATSUSHIMA, LUCIANA C. "Determinação das curvas de isodose e confirmação do planejamento em Radioterapia de Intensidade Modulada - IMRT convencional empregando as técnicas de termoluminescência, luminescência opticamente estimulada e detectores semicondutores." reponame:Repositório Institucional do IPEN, 2015. http://repositorio.ipen.br:8080/xmlui/handle/123456789/23694.

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Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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Trauernicht, Christoph Jan. "Measured and calculated dose distributions in the “claws” – a specially designed gold applicator loaded with I-125 seeds." Doctoral thesis, Faculty of Health Sciences, 2020. http://hdl.handle.net/11427/32371.

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Introduction: The “Claws” is a unique gold applicator for whole-eye radiotherapy that was designed at Groote Schuur Hospital. It is used to treat retinoblastoma. Under general anaesthesia, a pericorneal ring is attached to the four extraocular muscles, and four legs, each loaded with I125 seeds, are inserted beneath the conjunctiva in-between each pair of muscles and attached anteriorly to the ring. The four legs that are now sutured onto the ring give it a claw-like appearance, hence the name for the applicator. The applicator was designed in such a way that the dose is directed towards the middle of the eye, while sparing surrounding tissues. The dose to the organs at risk could never be determined accurately, because the treatment planning system (TPS) is not able to take into account the gold shielding. Additionally, the TPS approximates each seed as a point source and not as a line source, therefore not taking any anisotropy into account. Aims: The first aim of this project was to accurately determine various dosimetric and physical characteristics of a single I-125 seed and to then compare these to published data. Spectral measurements of the OncoSeed 6711 using various detectors were also done. The next aim was to formalize the model of the “Claws” so that the applicator can potentially also be manufactured elsewhere. The next aim was to describe the “Claws” dosimetrically. This was done - Using thermoluminescent dosimeters in a solid water phantom - Using gafchromic film in a solid water phantom - Using treatment planning systems TheraPlan Plus and BrachyVision - Using Monte Carlo simulations – egs_brachy The final aim of the thesis was the comparison of measured and calculated data. The Monte Carlo simulations take into account the seed anisotropy as well as the gold shielding; therefore the relative dose to critical structures can be estimated more reliably. Method and Materials: Gafchromic film and thermoluminescent dosimeters (TLDs) were used for measurements in various specially designed phantoms to determine the seed parameters, as well as dose distributions in the eye. Dose distributions were calculated on two treatment planning systems. A CAD drawing of the “Claws” was created and used to create the input file for Monte Carlo simulations using egs_brachy. The final Monte Carlo calculation simulated 64.000.000.000 particle histories at voxel sizes of 0.1 mm x 0.1 mm x 0.1 mm. Results: Measured seed data matched published seed data. Significant dose distribution changes were found when comparing measured and Monte Carlo data to planned data, especially near the periphery of the eye between adjacent legs. The Monte Carlo calculated dose to the optic nerve is 64.8 % of the central dose in the eye, while the planned dose is 93.7 %. The Monte Carlo lens dose varies from 72.0 % - 86.1 %, while the planned dose varies from 73.0 % - 84.3 %. Monte Carlo calculated dose to the bony orbit is 11.3 %, while the planned dose is 54.7 %. Conclusion: Measured seed data matched published seed data. The “Claws” were formalized with CAD drawings. Measured and Monte Carlo simulated dose distributions matched well, while planned dose distributions showed discrepancies in certain regions of the eye and outside of the eye. This clearly indicates that the gold shielding of the applicator walls must be taken into account during dose calculations. It can be concluded that the “Claws” were extensively described and characterized in this work.

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Beauvais, Hélène. "Modélisation des distributions de dose sur l'axe pour des faisceaux de photons de haute énergie utilisés en radiothérapie." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37602672c.

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Helal, Azza Mahmoud. "The effect of patient anatomy on optimised intensity modulated radiotherapy dose distributions for head and neck and prostate cancer." Thesis, University of Nottingham, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438639.

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Dejean-Viellard, Catherine. "Etude des techniques de régularisation en radiothérapie conformationnelle avec modulation d'intensité et évaluation quantitative des distributions de dose optimales." Toulouse 3, 2003. http://www.theses.fr/2003TOU30195.

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MIZUNO, ERICK Y. "Desenvolvimento e caracterização de um gel alanima para aplicação na medida da distribuição da dose de radiação usando a técnica de espectrofotometria." reponame:Repositório Institucional do IPEN, 2007. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11571.

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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

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Cecilio, Paulo José. "Implementação e aceite de sistema de radioterapia de feixe modulado dinâmico com o uso de colimador secundário de múltiplas folhas." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/85/85131/tde-03052012-094138/.

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A radioterapia de feixe de intensidade modulada (IMRT) no seu modo dinâmico é uma forma de radioterapia tri-dimensional (3D), na qual modula-se um feixe de forma a obter-se a irradiação com campos que possuem perfil variável. Os campos são gerados por um sistema de otimização matemático e transformado em seqüências de movimento ou abertura de lâminas dos colimadores terciários de múltiplas folhas (MLC) ou feixe colimado helicoidal, reproduzindo a fluência de radiação adequada. No processo o operador atribui valores limitantes de dose ao alvo e aos órgãos de risco circunvizinhos para que o sistema de planejamento inverso realize a otimização possível. Após a aprovação do plano de tratamento o mesmo deve ser conferido, através de um controle de qualidade (CQ), onde são verificadas as doses que deverão ser administradas ao paciente, comprovando-se as doses obtidas e aprovadas no plano do sistema de planejamento (SPC). Para este controle os mesmos feixes e campos são medidos em termos de dose absorvida e perfis, através de dosimetria na qual comprova-se que não há erro físico ou dosimétrico no plano que irá tratar o paciente com diferença aceitável de até 5%, também utilizada como tolerância para a aprovação dos 460 casos avaliados nesta tese. Foram apresentados as metodologias para a aceitação no primeiro serviço a utilizá-la no Brasil e os testes de controle de qualidade de dois serviços de radioterapia, desde agosto de 2001 à maio de 2006 e no outro serviço de outubro de 2007 a maio de 2008, com controle de qualidade que permitiram os respectivos tratamentos clínicos com dados de 4 anos, ou seja, 460 casos com 3935 campos de tratamento verificados individualmente por dosimetria. Isto possibilitou o aperfeiçoamento da metodologia e garantia da qualidade nos tratamentos de IMRT dinâmico destes pacientes.
The intensity modulated radiation therapy (IMRT) is a type of radiation therapy using dynamic sliding window which modulated the beamlets of each field which are thus obtained as a variable profile. The multiple fields are obtained by mathematic optimization in special treatment planning system. In this way, the resulted field is generated by leaf sequencing using the multi-leaf collimator (MLC) or helicoidally beam. The optimization is an interactive process with operator and planning system where the dose prescription to target and dose limit for organ of risk are inserted to obtain the acceptable beam fluence and this process is named as inverse planning. The planning approved by physician should checked by means of dosimetry in order to assure the correct dose delivery; this action is the main task of a quality control (QC) program. The QC is performed by measurements of total absorbed dose and profile for each field planned for the patient. The acceptance level is 5% for total dose and was used for all 460 cases and 3935 fields analyzed between August 2001 to May 2006 at Albert Einstein Hospital and October 2007 to May 2008 at the Centro Infantil Dr. Boldrini. This work performs an analysis of the QC of treatments plans for all patients treated with IMRT. During four years the methodologies were frequently improved and upgradated for each tumor site and could thus be assured for the required quality of all treatments with dynamic IMRT.

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Deniz, Daniel. "Causes of multimodality of efficiency gain distributions in accelerated Monte Carlo based dose calculations for brachytherapy planning using correlated sampling." Thesis, Linköping University, Department of Biomedical Engineering, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-56468.

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Fixed-collision correlated sampling for Monte Carlo (MC) simulations is a method which can be used in order to shorten the simulation time for brachytherapy treatment planning in a 3D patient geometry. The increased efficiency compared to conventional MC simulation is measured by efficiency gain. However, a previous study showed that, in some cases, PDFs (probability density functions) of estimates of the efficiency gain, simulated using resampling and other MC methods, were multimodal with values below 1. This means that the method was less effective than conventional sampling for these cases. The aims of this thesis were to trace the causes of the multimodal distributions and to propose techniques to mitigate the problem caused by photons with high statistical weights.Two simulation environments were used for the study case, a homogeneous and a heterogeneous environment. The homogenous environment consisted of a water sphere with the radius 100mm. For the heterogeneous environment a cylindrical block of tungsten alloy (diameter 15 mm, height 2.5 mm) was placed in the water sphere. The sphere was divided into an array of cubic voxels of size 2.5 mm x 2.5 mm x 2.5 mm for dose calculations. A photon source was positioned in the middle of the water sphere and emitted photons with the energy 400 keV.It was found that the low values and multimodal PDFs for the efficiency gain estimates originated from photons depositing high values of energy in some voxels in the heterogeneous environment. The high energy deposits were due to extremely high statistical weights of photons interacting repeatedly in the highly attenuating tungsten cylinder. When photon histories contributing to the rare events of high energy deposits (outliers) were removed, the PDFs became uni-modal and efficiency gain increased. However, removing outliers will cause results to be biased calling for other techniques to handle the problem with high statistical weights.One way to resolve the problem in the current implementation of the fixed-collision correlated sampling scheme in PTRAN (the MC code used) could be to split photons with high statistical weights into several photons with the same sum weight as the initial photon. The splitting of photons will result in more time consuming simulations in areas with high attenuation coefficients, which may not be the areas of interest. This could be resolved by using Russian roulette, eliminating some of the photons with high statistical weight in such areas.Fixed-collision correlated sampling for Monte Carlo (MC) simulations is a method which can be used in order to shorten the simulation time for brachytherapy treatment planning in a 3D patient geometry. The increased efficiency compared to conventional MC simulation is measured by efficiency gain. However, a previous study showed that, in some cases, PDFs (probability density functions) of estimates of the efficiency gain, simulated using resampling and other MC methods, were multimodal with values below 1. This means that the method was less effective than conventional sampling for these cases. The aims of this thesis were to trace the causes of the multimodal distributions and to propose techniques to mitigate the problem caused by photons with high statistical weights.Two simulation environments were used for the study case, a homogeneous and a heterogeneous environment. The homogenous environment consisted of a water sphere with the radius 100mm. For the heterogeneous environment a cylindrical block of tungsten alloy (diameter 15 mm, height 2.5 mm) was placed in the water sphere. The sphere was divided into an array of cubic voxels of size 2.5 mm x 2.5 mm x 2.5 mm for dose calculations. A photon source was positioned in the middle of the water sphere and emitted photons with the energy 400 keV.It was found that the low values and multimodal PDFs for the efficiency gain estimates originated from photons depositing high values of energy in some voxels in the heterogeneous environment. The high energy deposits were due to extremely high statistical weights of photons interacting repeatedly in the highly attenuating tungsten cylinder. When photon histories contributing to the rare events of high energy deposits (outliers) were removed, the PDFs became uni-modal and efficiency gain increased. However, removing outliers will cause results to be biased calling for other techniques to handle the problem with high statistical weights.One way to resolve the problem in the current implementation of the fixed-collision correlated sampling scheme in PTRAN (the MC code used) could be to split photons with high statistical weights into several photons with the same sum weight as the initial photon. The splitting of photons will result in more time consuming simulations in areas with high attenuation coefficients, which may not be the areas of interest. This could be resolved by using Russian roulette, eliminating some of the photons with high statistical weight in such areas.

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Moji, Kabelo McDonald. "Comparison of measured photon and electron beam dose distributions between 3D water phanton and profiler 2 scanning system, South Africa." Thesis, University of Limpopo (Medunsa Campus), 2013. http://hdl.handle.net/10386/1086.

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Thesis ( MSc ( Physics) ) -- University of Limpopo, 2013.
Background and Objectives: To establish whether the profiler 2 scanning system can be used as a substitute for the 3D-water phantom, by comparing the percentage depth doses and beam profiles for both the photons and electron beams, and validating the results using CMS XiO treatment planning system. Methods: Beam data (profiles, percentage depth doses and absolute dosimetry) were acquired for the two systems: (3D-water phantom and profiler 2 scanning system) for beam energies 6 MV and 15 MV photon beams, and 4, 6, 8, 10, 12 and 15 MeV electron beams generated by the Elekta Synergy linear accelerator (linac) for the field sizes of 6 × 6 cm2, 10 × 10 cm2, 14 × 14 cm2, 20 × 20 cm2, and 25 × 25 cm2 at depths of 0.5 cm, 1.0 cm, 2.0 cm, and 5.0 cm respectively. These measurements were acquired using ionization chambers in water and diode detectors in Perspex. The acquired data was sent to CMS XiO treatment planning system for validation. Results: In general, the dose distributions for both systems compared very well with uncertainties within recommended limits. The largest maximum difference in symmetry was 1.6 % for a 6 MV photon beam defined at 25 × 25 cm2 field size. The largest maximum difference in flatness was 2.77 % for a 4 MeV electron beam defined at 10 × 10 cm2 applicator size. The penumbra largest maximum difference was 1.708 cm for 8 MeV electron beam defined at 25 × 25 cm2 applicator size, which was outside the recommended limit of 1.2 cm. The largest maximum difference in field size was 2.388 cm for a 6 MeV electron beam defined at 20 × 20 cm2 applicator size, which was outside the recommended limit of 0.4 cm. The largest maximum difference in percentage depth dose at 10 cm depth was 1.69 % for the 6 MV photon beam. The absolute dose output measurements showed a very good agreement between the two systems to a maximum percentage difference and highest standard deviation of -0.99 % and 0.69 % respectively for the 6 MV photon beam. Validation measurements showed an agreement to less than 1 % and 2 mm for percentage depth doses and beam profiles respectively. Conclusion and recommendation: From the results obtained, it is evident that the profiler 2 scanning system can be used as a substitute for the 3D-water phantom beam data acquisitions during linear accelerator commissioning. The future work based on this study could be to study the limitations involved with the profiler 2 scanning system when used during measurements for commissioning of a linear accelerator. Limitations like field size (maximum field size of 20 × 30 cm2 at SSD = 100 cm), number of Perspex slabs to be used on top of the profiler 2 scanning system and diagonal profile measurements.

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Aryal, Prakash. "REEVALUATION OF THE AAPM TG-43 BRACHYTHERAPY DOSIMETRY PARAMETERS FOR AN ¹²⁵I SEED, AND THE INFLUENCE OF EYE PLAQUE DESIGN ON DOSE DISTRIBUTIONS AND DOSE-VOLUME HISTOGRAMS." UKnowledge, 2014. http://uknowledge.uky.edu/physastron_etds/14.

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The TG-43 dosimetry parameters of the AdvantageTM 125I model IAI-125A brachytherapy seed were studied. An investigation using modern MCNP radiation transport code with updated cross-section libraries was performed. Twelve different simulation conditions were studied for a single seed by varying the coating thickness, mass density, photon energy spectrum and cross-section library. The dose rate was found to be 6.3% lower at 1 cm in comparison to published results. New TG-43 dosimetry parameters are proposed. The dose distribution for a brachytherapy eye plaque, model EP917, was investigated, including the effects of collimation from high-Z slots. Dose distributions for 26 slot designs were determined using Monte Carlo methods and compared between the published literature, a clinical treatment planning system, and physical measurements. The dosimetric effect of the composition and mass density of the gold backing was shown to be less than 3%. Slot depth, width, and length changed the central axis (CAX) dose distributions by < 1% per 0.1 mm in design variation. Seed shifts in the slot towards the eye and shifts of the 125I-laden silver rod within the seed had the greatest impact on the CAX dose distribution, changing it by 14%, 9%, 4.3%, and 2.7% at 1, 2, 5, and 10 mm, respectively, from the inner scleral surface. The measured, full plaque slot geometry delivered 2.4% ± 1.1% higher dose along the plaque’s CAX than the geometry provided by the manufacturer and 2.2%±2.3% higher than Plaque SimulatorTM (PS) treatment planning software (version 5.7.6). The D10 for the simulated tumor, inner sclera, and outer sclera for the measured slot plaque to manufacturer provided slot design was 9%, 10%, and 19% higher, respectively. In comparison to the measured plaque design, a theoretical plaque having narrow and deep slots delivered 30%, 37%, and 62% lower D10 doses to the tumor, inner sclera, and outer sclera, respectively. CAX doses at –1, 0, 1, and 2 mm were also lower by a factor of 2.6, 1.72, 1.50, and 1.39, respectively. The study identified substantial sensitivity of the EP917 plaque dose distributions to slot design.

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POLI, MARIA E. R. "Dosimetria aplicada na irradiacao de toda a pele utilizando feixes de eletrons com energia nominal de 4 MeV." reponame:Repositório Institucional do IPEN, 2000. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10813.

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GROPPO, DANIELA P. "Caracterização dosimétrica de amostras de BeO em feixes de radiação alfa, beta e X por técnicas luminescentes." reponame:Repositório Institucional do IPEN, 2013. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10576.

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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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FERAUCHE, DEBORA C. "Desenvolvimento de um sistema de dosimetria in vivo por meio de filmes portals para o controle da qualidade de tratamentos radioterapeuticos." reponame:Repositório Institucional do IPEN, 2002. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11006.

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45

Taulbee, Timothy Dale. "Measurement and model prediction of proton-recoil track length distributions in NTA film dosimeters for neutron energy spectroscopy and retrospective dose assessment." Cincinnati, Ohio : University of Cincinnati, 2009. http://www.ohiolink.edu/etd/view.cgi?acc_num=ucin1235764236.

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Thesis (Ph.D.)--University of Cincinnati, 2009.
Advisors: Henry Spitz PhD (Committee Chair), Bingjing Su PhD (Committee Member), John Christenson PhD (Committee Member). Title from electronic thesis title page (viewed May 1, 2009). Keywords: NTA; proton-recoil; neutron spectroscopy; dose assessment; track length; Monte Carlo; neutron transport; neutron interactions. Includes abstract. Includes bibliographical references.

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Niemkiewicz, John. "A study on the use of removal-diffusion theory to calculate neutron distributions for dose determination in boron neutron capture therapy /." The Ohio State University, 1996. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487934589976468.

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47

FONSECA, GABRIEL P. "Projeto e construcao de placas espalhadoras e degradadoras de energia para uso em radioterapia com feixe de eletrons para doencas de pele." reponame:Repositório Institucional do IPEN, 2010. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9550.

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TADA, ARIANE. "Analise dosimetrica de fontes de radiacao para uso em lesoes dermatologicas." reponame:Repositório Institucional do IPEN, 2010. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9551.

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Albaret, Claude. "Automated system for Monte Carlo determination of cutout factors of arbitrarily shaped electron beams and experimental verification of Monte Carlo calculated dose distributions." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=81259.

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Dose predictions by Monte-Carlo (MC) techniques could alleviate the measurement load required in linac commissioning and clinical radiotherapy practice, where small or irregular electron fields are routinely encountered. In particular, this study focused on the MC calculation of cutout factors for clinical electron beams. A MC model for a Varian linac CL2300C/D was built and validated for all electron energies and applicators. A MC user code for simulation of irregular cutouts was then developed and validated. Supported by a home-developed graphical user interface, it determines in situ cutout factors and depth dose curves for arbitrarily shaped electron fields and collects phase space data. Overall, the agreement between simulations and measurements was excellent for fields larger than 2 cm.
The MC model was also used to calculate dose distributions with the fast MC code XVMC in CT images of phantoms of clinical interest. These dose distributions were compared to dose calculations performed by the pencil-beam algorithm-based treatment planning system CadPlan and verified against measurements. Good agreement between calculations and measurements was achieved with both systems for phantoms containing 1-dimensional heterogeneities, provided a minimal quality of the CT images. In phantoms with 3-dimensional heterogeneities however, CadPlan appeared unable to predict the dose accurately, whereas MC provided with a more satisfactory dose distribution, despite some local discrepancies.

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ANTUNES, PAULA C. G. "Reconstrucao de objetos simuladores segmentados aplicaveis a dosimetria de pele." reponame:Repositório Institucional do IPEN, 2010. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9614.

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Dissertations / Theses on the topic 'Distributions de dose'

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