Дисертації з теми "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.
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.
Milette, Marie-Pierre. "Direct optimization of 3D dose distributions using collimator rotation." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/274.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
Bero, Mamdouh A. "Development of a three-dimensional radiation dosimetry system." Thesis, University of Surrey, 2001. http://epubs.surrey.ac.uk/719/.
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
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
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.
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.
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.
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.
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.
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
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.
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/.
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.
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
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
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.
Science, Faculty of
Physics and Astronomy, Department of
Graduate
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.
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.
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.
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
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
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
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.
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.
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.
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.
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
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/.
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.
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.
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.
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.
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.
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.
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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Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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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Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
Hepworth, Stephen J. "Investigations into polymer gel dosimetry using magnetic resonance imaging." Thesis, University of Surrey, 2000. http://epubs.surrey.ac.uk/978/.
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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Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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.
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.
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.
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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Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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.
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.
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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Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP