No presente trabalho serão apresentados testes de comissionamento e de avaliação da utilização do portal dosimetry, da Varian, no controle de qualidade dos planejamentos de radioterapia de intensidade modulada. Os testes de comissionamento foram realizados para caracterizar o portal dosimetry em termos dosimétricos e para avaliar a sua possível aplicação em radioterapia. Esses testes demonstraram que o portal dosimetry possui todas as características necessárias para ser utilizado em dosimetria na radioterapia tais como linearidade da resposta com a dose, independência com a taxa de dose, reprodutibilidade, dentre outras. A avaliação da utilização do portal dosimetry no controle de qualidade de IMRT foi realizada em duas etapas: avaliação da capacidade do dispositivo em detectar erros propositalmente introduzidos em fluências simples e em fluências complexas. Foram introduzidos erros de magnitude conhecida em áreas determinadas das fluências e foi realizado o controle de qualidade dessas fluências com o portal dosimetry e com mais três sistemas dosimétricos: câmara de ionização, filme e matriz de câmaras de ionização. Os dados obtidos com o portal foram comparados com os dos outros dispositivos e todos foram capazes de identificar os erros introduzidos de maneira satisfatória, sendo os valores, normalizados para a fluência original, obtidos com o dosímetro portal indênticos aos da câmara de ionização e aos da matriz de câmaras de ionização (seven29) e diferindo em até 2% dos valores obtidos com os filmes. As fluências medidas com o portal dosimetry foram avaliadas em termos quantitativos e qualitativos. Os índices da função gama fornecidos pelo software de análise do portal dosimetry não apresentaram regras definidas de comportamento em relação aos erros introduzidos e por essa razão a análise qualitativa se mostrou indispensável nos casos avaliados. / In this paper we present commissioning testing and evaluation of the use of Varians portal dosimetry in the quality assurance of intensity-modulated radiotherapy. The commissioning tests were performed to characterize the portal dosimetry in terms dosimetric and to assess the its possible application in radiotherapy. These tests demonstrated that portal dosimetry has all the characteristics to be used for dosimetry in radiotherapy such as linear response with dose, the independence of dose rate, reproducibility, and others. The evaluation of the use of portal dosimetry in quality control of IMRT was performed in two steps: assessing the ability of the device to detect errors deliberately introduced in simple and complex fluences. Errors of known magnitude were introduced in certain areas of fluences and was carried out quality control of these fluences with portal dosimetry and three dosimetric systems: ionization chamber, film and array of ionization chambers. The data obtained from the portal were compared with those of other devices and all were able to identify errors introduced satisfactorily, the values, normalized to the original fluence, obtained with the portal dosimetry were similar to the ionization chamber and the array of ion chambers (seven29) and differing in up to 2% of the values obtained with the films. The fluences measured with the portal dosimetry were evaluated both quantitatively and qualitatively. The index of the gamma function provided by software analysis of portal dosimetry showed no defined rules of behavior in relation to the errors introduced and for this reason the qualitative analysis has proved indispensable in cases evaluated.

Le rêve ultime du radiothérapeute a toujours été d’avoir à disposition des technologies capables de délivrer avec une parfaite précision des doses élevées aux volumes tumoraux sans irradier les tissus sains avoisinants. Ce rêve ne deviendra jamais réalité, mais tous les efforts des physiciens, médecins et industriels doivent être combinés pour que la réalité s’approche le plus possible de cette utopie. Depuis le début des années 60 et l’avènement des accélérateurs linéaires d’électrons montés sur des unités de traitement, la technologie en thérapie par photons a évolué énormément. Aujourd’hui, les traitements les plus à la pointe incluent la radiothérapie par modulation d’intensité (« Intensity-Modulated Radiation Therapy » ou IMRT) avec l’aide d’outils d’imagerie hautement sophistiqués. L’IMRT est une technique complexe qui requiert un excellent contrôle de la précision dans toutes les étapes du processus du traitement. Ces étapes peuvent être résumées en trois catégories qui sont 1) l’étalonnage et la stabilité de l’unité de traitement, 2) le positionnement et la qualité des données associées au patient et 3) la précision du calcul de dose effectué lors de la planification du traitement. Pour améliorer l’incertitude globale d’un traitement donné, des efforts de recherche sont nécessaires dans les trois catégories. Cette thèse se concentre sur le processus de calcul de dose. Durant les dernières décennies, la complexité et la précision des algorithmes de dose ont augmenté fortement grâce aux énormes progrès de l’informatique. Malgré cela, l’immense majorité des algorithmes utilisent des méthodes analytiques impliquant des approximations importantes au niveau de la physique de transport des particules. Il est cependant possible de concevoir des algorithmes qui évitent ces approximations en se basant sur des méthodes dites de Monte Carlo (MC) qui simulent fidèlement la réalité physique et qui sont considérées aujourd’hui comme les plus précises de calcul de la dose dans les tissus humains. Malheureusement, jusqu’à récemment, la vitesse des simulations MC était trop lente pour être compatible avec les contraintes de temps liées à la routine clinique. Mais les progrès continus en puissance de calcul combinés avec l’introduction de simplifications pertinentes dans les codes MC permettent d’envisager l’introduction d’algorithmes MC en routine clinique, ce qui est déjà le cas pour plusieurs systèmes de planification de traitement commerciaux. L’objectif de cette thèse était d’évaluer la valeur ajoutée du MC comparé à des algorithmes analytiques modernes pour des traitements IMRT complexes de tumeurs entourées de nombreuses inhomogénéités de densité. Ces évaluations ont été effectuées pour deux techniques de traitement IMRT : « step-and-shoot » et tomothérapie hélicoïdale. Pour l’IMRT « step-and-shoot » délivrée par une unité de traitement Elekta SL25, des simulations MC avec BEAMnrc ont été comparées avec un algorithme commercialisé récemment par la firme Varian appelé « Anisotropic Analytical Algorithm » (AAA). Pour la tomothérapie, une étude similaire a été accomplie mais pour le code utilisé dans le système fourni par « Tomotherapy Incorporated » et basé sur un algorithme de type convolution/superposition utilisant l’approximation « collapsed-cone ». Durant cette seconde étude, la modélisation MC au moyen du code MC PENELOPE était un aspect très important étant donné que c’est la première fois qu’un code MC complet pour la tomothérapie était construit avec tous les détails techniques de la machine fournis par le constructeur. De plus, le modèle MC, appelé TomoPen, a été conçu en vue d’une introduction future dans le système clinique. La vitesse de la simulation était donc une contrainte importante. La stratégie utilisée pour la simulation et adoptée dans TomoPen consiste principalement à simplifier drastiquement le transport des photons dans le collimateur multilames et permet de calculer des distributions de dose dans une tumeur bilatérale de la sphère tête et cou en à peu près 10 heures sur un processeur de 2 GHz, sans perte de précision significative. En utilisant le groupe d’ordinateurs fourni avec chaque unité de traitement de tomothérapie, ce temps de simulation peut être réduit d’un facteur 32, correspondant au nombre de processeurs. Durant cette thèse, la correspondance entre algorithmes analytiques et MC était en général satisfaisante pour la majorité des cas cliniques et expérimentaux étudiés. Cependant, des différences ont pu être observées pour des situations critiques, comme des petites tumeurs pulmonaires ou des tumeurs ethmoïdes. Même si ces déviations n’étaient pas « dramatiques », elles ont pu démontrer clairement le potentiel des algorithmes MC dans la pratique clinique afin d’améliorer la qualité globale et la précision des traitements.

To optimize the beam angle and fluence map in Intensity Modulated Radiation Therapy (IMRT) planning, we apply Benders decomposition as well as develop a two-stage integer programming-based heuristic. Benders decomposition is first implemented in the traditional manner by iteratively solving the restricted master problem, and then identifying and adding the violated Benders cut. We also implemented Benders decomposition using the “lazy constraint” feature included in CPLEX. In contrast, our two-stage heuristic first seeks to find a good solution by iteratively eliminating the least used angles in the linear programming relaxation solution until the size of the formulation is manageable. In the second stage of the heuristic, the solution is improved by applying local branching. The various methods were tested on real patient data in order to investigate their effectiveness and runtime characteristics. The results indicated that implementing Benders using the lazy constraint usually led to better feasible solutions than the traditional approach. Moreover, the LP rounding heuristic was seen to generate high-quality solutions within a short amount of time, with further improvement obtained with the local branching search. / text

The purpose of this work is to evaluate quasi-3D arrays for use with intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) and to determine their clinical relevance. This is achieved using a Delta4 from Scandidos and ArcCheck from Sun Nuclear and the associated software. While certain aspects of these devices and software have been previously evaluated, the main goal of this work is to evaluate the new aspects, such as reconstructing dose on a patient CT set, and extending the capabilities. This includes the capability to reconstruct the dose based on a helical delivery as well as studying the dose to a moving target using measurement-guided motion simulations. It was found that Sun Nuclear's ArcCheck/3DVH system exhibited excellent agreement for dose reconstruction for IMRT/VMAT using a traditional C-arm linear accelerator and stringent 2%/2mm comparison constraints. It also is a powerful tool for measurement-guided dose estimates for moving targets, allowing for many simulations to be performed based on one measurement and the target motion data. For dose reconstruction for a helical delivery, the agreement was not as good for the stringent comparison but was reasonable for the clinically acceptable 3%/3mm comparison. Scandidos' Delta4 shows good agreement with stringent 2%/2mm constraints for its dose reconstruction on the phantom. However, the dose reconstruction on the patient CT set was poor and needs more work. Overall, it was found that quasi-3D arrays are powerful tools for dose reconstruction and treatment plan comparisons. The ability to reconstruct the dose allows for a dose resolution comparable to the treatment plan, which negates the previous issues with inadequate sampling and resolution issues found when just comparing the diodes. The ability to quickly and accurately compare many plans and target motions with minimum setup makes the quasi-3D array an attractive tool for both commissioning and patient specific quality assurance.

Intensity Modulated Radiation Therapy (IMRT) is a modern radiotherapy treatment technique used to obtain highly conformal dose distributions. The delivery of IMRT is commonly achieved through the use of a multileaf collimator (MLC). One of the hindrances at present to the widespread use of IMRT is the increased time required for its planning, delivery and verification. In this thesis one particular method of MLC based IMRT, known as Static Multileaf Collimator based IMRT (SMLC-IMRT), has been studied along with methods for improving it???s delivery efficiency. The properties of an MLC commonly used in SMLC-IMRT have been characterised. The potential ramifications of these properties on the dosimetric accuracy of the delivered IMRT field were also investigated. An Interactive Leaf Sequencing (ILS) program was developed that allowed for the manipulation and processing of intensity maps using a variety of methods. The objective of each method was to improve the delivery efficiency whilst maintaining the dosimetric quality of the IMRT treatment. The different methods investigated were collimator angle optimisation, filtration, and intensity level optimisation. The collimator was optimised by identifying the angle at which the minimum monitor unit???s (MU???s) were required when using a sliding-window delivery method. A Savitzky-Golay filter was applied to random intensity maps and suitable filtration parameters identified for filtering clinical IMRT fields, and the intensity levels were optimised based on a deviation threshold. The deviation threshold identified the acceptable level of difference tolerable between the original and modified intensity map. Several IMRT cases were investigated and the impact of each the methods on MU???s, segments and dose distribution observed. As the complexity of IMRT fields increases the dosimetric impact of the MLC properties increases. Complex SMLC-IMRT fields require longer delivery times due to the increased number of MU???s and segments. Collimator optimisation was shown to be a fast and effective means of improving delivery efficiency with negligible dosimetric change to the optimised plan. Modifying intensity maps by applying a filter and optimising the intensity levels did reduce the complexity and improve the delivery efficiency, but also required a dosimetric compromise of the optimised plan.

No description available.

Enhanced resistance to radiation could be caused by both chronic hypoxia and acute hypoxic which has been reported in prostate cancer in various studies. Therefore currently used dose prescriptions (70Gy in 35 fractions) for external beam radiation therapy (EBRT) of prostate cancer has been suggested insufficient to provide optimum clinical outcome. In this study, we propose a Biologically Guided Radiation Therapy approach to boost dose in hypoxic prostate tumor regions while sparing the urethra. A previously proposed hypoxia model was modified for prostate cancer and incorporated into treatment plan optimization. The concept of equivalent uniform dose (EUD) was used in the optimization and evaluation of results. CT data from 25 prostate cancer patients who recently received EBRT at the British Columbia Cancer Agency (BCCA) and hypothetical hypoxic regions manually drawn on these CT scans were selected for this study. The results show that our methods could boost dose in target volume to substantially higher levels. EUD of planning target volume increased to more than 80Gy, despite accounting for effects of hypoxia. This increase was achieved with only minor changes in dose in normal tissues, typically less than 5Gy. Notably, urethra sparing was excellent with a EUD around 64Gy. Robustness of the proposed approach is verified against various hypoxic settings. EUD comparison between RT plans in biological guided and conventional approaches using the same RT technique (Volumetric Modulated Arc Therapy) also suggests that biologically guided radiation therapy (BGRT) approach is more suitable for dose painting purposes with the advantage of delivering sufficient dose to hypoxia region in different scenarios and sparing normal tissue better. Furthermore, we also investigated the impact of inter-fraction patient set-up error and intra-fraction organ motion on the high dose gradients achieved with this proposed dose painting method and explored the feasibility of adapting geometrical uncertainties (represented as systematic error and random error) into treatment planning. Image error obtained from EPID images are used to derive systematic uncertainty and random uncertainty. During the geometrical uncertainty adapted optimization, dose matrix in PTV is shifted based on systematic error and convolved with a Gaussian kernel which is pre-calculated using random error. CT sets and organ contours from five patients who enrolled in the previous dose painting i study are selected. For each of them, seven plans are generated using cumulated uncertainty data which was collected after every five fractions. We also present the outcome in terms of equivalent uniform dose (EUD). For four of the patients, EUD history of all seven plans suggests using the proposed optimization method with uncertainty data from the first five fractions, it is possible to achieve the same target coverage of static treatment plans (difference in EUD less than 1Gy). Meanwhile, the elimination of PTV margin also leads to a significant dose reduction (more than 15Gy) in rectum.

Enhanced resistance to radiation could be caused by both chronic hypoxia and acute hypoxic which has been reported in prostate cancer in various studies. Therefore currently used dose prescriptions (70Gy in 35 fractions) for external beam radiation therapy (EBRT) of prostate cancer has been suggested insufficient to provide optimum clinical outcome. In this study, we propose a Biologically Guided Radiation Therapy approach to boost dose in hypoxic prostate tumor regions while sparing the urethra. A previously proposed hypoxia model was modified for prostate cancer and incorporated into treatment plan optimization. The concept of equivalent uniform dose (EUD) was used in the optimization and evaluation of results. CT data from 25 prostate cancer patients who recently received EBRT at the British Columbia Cancer Agency (BCCA) and hypothetical hypoxic regions manually drawn on these CT scans were selected for this study. The results show that our methods could boost dose in target volume to substantially higher levels. EUD of planning target volume increased to more than 80Gy, despite accounting for effects of hypoxia. This increase was achieved with only minor changes in dose in normal tissues, typically less than 5Gy. Notably, urethra sparing was excellent with a EUD around 64Gy. Robustness of the proposed approach is verified against various hypoxic settings. EUD comparison between RT plans in biological guided and conventional approaches using the same RT technique (Volumetric Modulated Arc Therapy) also suggests that biologically guided radiation therapy (BGRT) approach is more suitable for dose painting purposes with the advantage of delivering sufficient dose to hypoxia region in different scenarios and sparing normal tissue better. Furthermore, we also investigated the impact of inter-fraction patient set-up error and intra-fraction organ motion on the high dose gradients achieved with this proposed dose painting method and explored the feasibility of adapting geometrical uncertainties (represented as systematic error and random error) into treatment planning. Image error obtained from EPID images are used to derive systematic uncertainty and random uncertainty. During the geometrical uncertainty adapted optimization, dose matrix in PTV is shifted based on systematic error and convolved with a Gaussian kernel which is pre-calculated using random error. CT sets and organ contours from five patients who enrolled in the previous dose painting i study are selected. For each of them, seven plans are generated using cumulated uncertainty data which was collected after every five fractions. We also present the outcome in terms of equivalent uniform dose (EUD). For four of the patients, EUD history of all seven plans suggests using the proposed optimization method with uncertainty data from the first five fractions, it is possible to achieve the same target coverage of static treatment plans (difference in EUD less than 1Gy). Meanwhile, the elimination of PTV margin also leads to a significant dose reduction (more than 15Gy) in rectum.

Intensity Modulated Radiation Therapy (IMRT) is a modern radiotherapy treatment technique used to obtain highly conformal dose distributions. The delivery of IMRT is commonly achieved through the use of a multileaf collimator (MLC). One of the hindrances at present to the widespread use of IMRT is the increased time required for its planning, delivery and verification. In this thesis one particular method of MLC based IMRT, known as Static Multileaf Collimator based IMRT (SMLC-IMRT), has been studied along with methods for improving it???s delivery efficiency. The properties of an MLC commonly used in SMLC-IMRT have been characterised. The potential ramifications of these properties on the dosimetric accuracy of the delivered IMRT field were also investigated. An Interactive Leaf Sequencing (ILS) program was developed that allowed for the manipulation and processing of intensity maps using a variety of methods. The objective of each method was to improve the delivery efficiency whilst maintaining the dosimetric quality of the IMRT treatment. The different methods investigated were collimator angle optimisation, filtration, and intensity level optimisation. The collimator was optimised by identifying the angle at which the minimum monitor unit???s (MU???s) were required when using a sliding-window delivery method. A Savitzky-Golay filter was applied to random intensity maps and suitable filtration parameters identified for filtering clinical IMRT fields, and the intensity levels were optimised based on a deviation threshold. The deviation threshold identified the acceptable level of difference tolerable between the original and modified intensity map. Several IMRT cases were investigated and the impact of each the methods on MU???s, segments and dose distribution observed. As the complexity of IMRT fields increases the dosimetric impact of the MLC properties increases. Complex SMLC-IMRT fields require longer delivery times due to the increased number of MU???s and segments. Collimator optimisation was shown to be a fast and effective means of improving delivery efficiency with negligible dosimetric change to the optimised plan. Modifying intensity maps by applying a filter and optimising the intensity levels did reduce the complexity and improve the delivery efficiency, but also required a dosimetric compromise of the optimised plan.

Dissertação (mestrado)—Universidade de Brasília, Faculdade Gama, Programa de Pós-Graduação em Engenharia Biomédica, 2015. / Submitted by Fernanda Percia França (fernandafranca@bce.unb.br) on 2016-06-06T17:55:07Z No. of bitstreams: 1 2015_LuisFelipeOliveiraeSilva.pdf: 5470471 bytes, checksum: 1fe65af174596febff5a94a7a05ae399 (MD5) / Approved for entry into archive by Raquel Viana(raquelviana@bce.unb.br) on 2016-06-15T11:30:22Z (GMT) No. of bitstreams: 1 2015_LuisFelipeOliveiraeSilva.pdf: 5470471 bytes, checksum: 1fe65af174596febff5a94a7a05ae399 (MD5) / Made available in DSpace on 2016-06-15T11:30:22Z (GMT). No. of bitstreams: 1 2015_LuisFelipeOliveiraeSilva.pdf: 5470471 bytes, checksum: 1fe65af174596febff5a94a7a05ae399 (MD5) / A radioterapia de intensidade modulada (IMRT, do inglês intensitymodulatedradiotherapy) proporciona distribuições de dose bastante complexas, com regiões de alto gradiente de dose. Essa complexidade representa um desafio maior no controle de qualidade (CQ) quando se compara a IMRT com a radioterapia convencional. O objetivo do presente trabalho foi desenvolver e avaliar um sistema de cálculo de dose independente, chamado SCI, para o controle de qualidade da IMRT do tipojawsonly. O software desenvolvido utiliza um algoritmo de cálculo de dose baseado em correções realizadas no fator de calibração do acelerador linear, por meio de fatores tabelados, derivados de medições e calculados a partir de simples modelagem. Os próprios dados gerados no comissionamento são usados para alimentar o algoritmo.Os cálculos são realizados em um plano de um fantoma retangular. Para validar o SCI, comparações entre as previsões dosimétricas do sistema e outras referências foram realizadas. Foram comparados: doses pontuais no centro de campos assimétricos medidos com câmara de ionização; perfis de campos medidos com filme radiocrômico e com câmara de ionização; distribuições planares de dose de cinco casos de câncer de próstata e cinco de cabeça e pescoço medidas com um arranjo bidimensional de câmaras de ionização e calculadas pelo sistema de planejamento de tratamento (SPT). A avaliação foi realizada utilizando diferenças percentuais de dose, a menor diferença de posição em que se encontra o mesmo valor de dose (DTA, do inglês distancetoagreement) e a avaliação gama com critérios: (i) diferença máxima de dose de 3%, DTA de 3 mm; (ii) diferença máxima de dose 5%, DTA de 3 mm; e (iii) diferença máxima de dose 5%, DTA de 5 mm. As diferenças encontradas nas comparações entre as doses obtidas no centro de campos assimétricos foram menores do que 2,5%.As diferenças nos perfis dos campos quadrados menores do que 30x30 cm2 foram menores do que 2% ou 2mm. Os campos menores, medidos com filme, apresentaram diferenças mais consideráveis (DTAs de até 5 mm foram observadas). Esse resultado já era esperado devido à maior resolução espacial do filme quando comparada à da câmara de ionização (volume sensível de 0,125 cc). As avaliações gama usando tanto as medições quanto o SPT como referência sugerem que o SCI representa a distribuição de dose real segundo o critério de 5% de diferença máxima de dose e 5 mm de DTA, uma vez que a média de pontos aprovados foi superior a 96,5% (p<0,001) em todos os casos quando esse critério foi utilizado. O sistema também apresenta um boa representação segundo o critério de 5% de diferença máxima de dose e 3 mm de DTA (média de pontos aprovados superior a 92,0%; p<0,01). As médias de pontos aprovados com esses dois critérios estão, portanto, de acordo com os valores tipicamente usados como referência por profissionais da área de radioterapia. Desta forma, o sistema desenvolvido no presente trabalho está pronto para ser utilizado para o CQ de IMRT do tipo jawsonly sem custo adicional em relação aos equipamentos já utilizados, reduzindo o fluxo de trabalho comparado a métodos mais tradicionais e sem ocupação adicional da máquina de tratamento. / Intensity modulated radiation therapy (IMRT) provides complex dose distributions with high dose gradient regions. This complexity is a major challenge for quality assurance (QA), specially when comparing IMRT with conventional radiotherapy. In this research, I propose, develop, and evaluate an independent dose calculation system for QA of jaws only IMRT (JOIMRT). The developed software uses a dose calculation algorithm based on corrections performed over the linear accelerator (linac) calibration factor. In order to perform this corrections I used tabulated factors derived from measurements and calculated from simple modeling. Also, I used the linac's commissioning data as input to the algorithm.The developed system then performs the main computations over a rectangular phantom plan. To validate the proposed system, I compared the predictions of the dosimetric system with references that are commonly used in the literature. Specifically, I compared: point doses in the center of asymmetric field measured with an ionization chamber; dose profiles measured with radiochromic film and an ionization chamber; planar dose distributions of five of prostate and five head and neck cases measured with a two-dimensional array of ionization chambers and calculated by the treatment planning system (TPS). The evaluation was performed using percentage dose differences, distance to agreement (DTA) and gamma evaluation with tree criterions: (i) maximum difference dose of 3% and 3 mm DTA, (ii) maximum difference dose of 5% and 3 mm DTA, and (iii) maximum difference dose of 5% and 5 mm DTA. The differences in the comparisons between the doses obtained in the center of asymmetric fields were smaller than 2.5%. Differences in the profiles of square fields up to 30x30 cm2 were smaller than 2% or 2 mm. Smaller fields measured with film showed more significant differences (I measured DTAs up to 5 mm). This result was expected because of the higher spatial resolution of the film, as compared to the ionization chamber that provided the measurements used as inputs to the calculation algorithm (sensitive volume of 0.125 cc). The point approval ratings using both measurements and the TPS as a reference suggest that the independent dose calculation system represents the actual dose distribution according to the criterion of 5 % maximum dose difference and 5 mm DTA, since the average was approved points above 96.5% (<0,001) in all cases when this criterion was used. The system also features a good representation according to the criterion of 5% maximal dose difference and 3 mm DTA (average of approved points above 92.0%; p <0.01). Therefore, the average of approved points obtained with those two criteria satisfies the values typically used as references by radiotherapy professionals. In this way, the system I developed is ready to be used for the JOIMRT QA with no additional cost with respect to equipment already used, reducing the workload compared to more traditional methods and without additional treatment machine occupation.