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

Cette thèse a été réalisée dans le cadre de la dosimétrie des faisceaux de haute énergie délivrés au patient pendant un traitement de radiothérapie externe. L'objectif de ce travail est de vérifier que la distribution de dose 3D absorbée dans le patient est conforme au calcul réalisé sur le système de planification de traitement (TPS) à partir de l'imageur portal (en anglais : Electronic Portal Imaging Device, EPID). L'acquisition est réalisée en mode continu avec le détecteur aS-1200 au silicium amorphe embarqué sur la machine TrueBeam STx (VARIAN Medical system, Palo Alto, USA). Les faisceaux ont une énergie de 10 MeV et un débit de 600 UM.min-1. La distance source-détecteur (DSD) est de 150 cm. Après correction des pixels défectueux, une étape d'étalonnage permet de convertir leur signal en dose absorbée dans l'eau via une fonction de réponse. Des kernels de correction sont également utilisés pour prendre en compte la différence de matériaux entre l'EPID et l'eau et pour corriger la pénombre sur les profils de dose. Un premier modèle de calcul a permis ensuite de rétroprojeter la dose portale en milieu homogène en prenant en compte plusieurs phénomènes : les photons diffusés provenant du fantôme et rajoutant un excès de signal sur les images, l'atténuation des faisceaux, la diffusion dans le fantôme, l'effet de build-up et l'effet de durcissement du faisceau avec la profondeur. La dose reconstruite est comparée à celle calculée par le TPS avec une analyse gamma globale (3% du maximum de dose et 3 mm de DTA). L'algorithme a été testé sur un fantôme cylindrique homogène et sur un fantôme de pelvis à partir de champs modulés en intensité (RCMI) et à partir de champs d'arcthérapie volumique modulés, VMAT selon l'acronyme anglais Volumetric Modulated Arc Therapy. Le modèle a ensuite été affiné pour prendre en compte les hétérogénéités traversées dans le milieu au moyen des distances équivalentes eau dans une nouvelle approche de dosimétrie plus connue sous le terme de " in aqua vivo " (1). Il a été testé sur un fantôme thorax et, in vivo sur 10 patients traités pour une tumeur de la prostate à partir de champs VMAT. Pour finir, le modèle in aqua a été testé sur le fantôme thorax avant et après y avoir appliqué certaines modifications afin d'évaluer la possibilité de détection de sources d'erreurs pouvant influencer la bonne délivrance de la dose au patient.[...] / This thesis aims at the dosimetry of high energy photon beams delivered to the patient during an external radiation therapy treatment. The objective of this work is to use EPID the Electronic Portal Imaging Device (EPID) in order to verify that the 3D absorbed dose distribution in the patient is consistent with the calculation performed on the Treatment Planning System (TPS). The acquisition is carried out in continuous mode with the aS-1200 amorphous silicon detector embedded on the TrueBeam STx machine (VARIAN Medical system, Palo Alto, USA) for 10MV photons with a 600 UM.min-1 dose rate. The source-detector distance (SDD) is 150 cm. After correction of the defective pixels, a calibration step is performed to convert the signal into an absorbed dose in water via a response function. Correction kernels are also used to take into account the difference in materials between EPID and water and to correct penumbra. A first model of backprojection was performed to reconstruct the absorbed dose distribution in a homogeneous medium by taking into account several phenomena: the scattered photons coming from the phantom to the EPID, the attenuation of the beams, the diffusion into the phantom, the build-up, and the effect of beam hardening with depth. The reconstructed dose is compared to the one calculated by the TPS with global gamma analysis (3% as the maximum dose difference criteria and 3mm as the distance to agreement criteria). The algorithm was tested on a homogeneous cylindrical phantom and a pelvis phantom for Intensity-Modulated Radiation Therapy (IMRT) and (Volumetric Arc Therapy (VMAT) technics. The model was then refined to take into account the heterogeneities in the medium by using radiological distances in a new dosimetrical approach better known as "in aqua vivo" (1). It has been tested on a thorax phantom and, in vivo on 10 patients treated for a prostate tumor from VMAT fields. Finally, the in aqua model was tested on the thorax phantom before and after making some modifications to evaluate the possibility of detecting errors that could affect the correct delivery of the dose to the patient. [...]

IMRT uses non-uniform beam intensities within a radiation field to provide patient-specific dose shaping, resulting in a dose distribution that conforms tightly to the planning target volume (PTV). Unavoidable geometric uncertainty arising from patient repositioning and internal organ motion can lead to lower conformality index (CI), a decrease in tumor control probability (TCP) and an increase in normal tissue complication probability (NTCP). The CI of the IMRT plan depends heavily on steep dose gradients between the PTV and organ at risk (OAR). Geometric uncertainties reduce the planned dose gradients and result in a less steep or “blurred” dose gradient. The blurred dose gradients can be maximized by constraining the dose objective function in the static IMRT plan or by reducing geometric uncertainty during treatment with corrective verification imaging. Internal organ motion and setup error were evaluated simultaneously for 118 individual patients with implanted fiducials and MV electronic portal imaging (EPI). The Gaussian PDF is patient specific and group standard deviation (SD) should not be used for accurate treatment planning for individual patients. Frequent verification imaging should be employed in situations where geometric uncertainties are expected. The dose distribution including geometric uncertainties was determined from integration of the convolution of the static dose gradient with the PDF. Local maximum dose gradient (LMDG) was determined via optimization of dose objective function by manually adjusting DVH control points or selecting beam numbers and directions during IMRT treatment planning. EUDf is a useful QA parameter for interpreting the biological impact of geometric uncertainties on the static dose distribution. The EUDf has been used as the basis for the time-course NTCP evaluation in the thesis. Relative NTCP values are useful for comparative QA checking by normalizing known complications (e.g. reported in the RTOG studies) to specific DVH control points. For prostate cancer patients, rectal complications were evaluated from specific RTOG clinical trials and detailed evaluation of the treatment techniques. Treatment plans that did not meet DVH constraints represented additional complication risk. Geometric uncertainties improved or worsened rectal NTCP depending on individual internal organ motion within patient.

IMRT uses non-uniform beam intensities within a radiation field to provide patient-specific dose shaping, resulting in a dose distribution that conforms tightly to the planning target volume (PTV). Unavoidable geometric uncertainty arising from patient repositioning and internal organ motion can lead to lower conformality index (CI), a decrease in tumor control probability (TCP) and an increase in normal tissue complication probability (NTCP). The CI of the IMRT plan depends heavily on steep dose gradients between the PTV and organ at risk (OAR). Geometric uncertainties reduce the planned dose gradients and result in a less steep or “blurred” dose gradient. The blurred dose gradients can be maximized by constraining the dose objective function in the static IMRT plan or by reducing geometric uncertainty during treatment with corrective verification imaging. Internal organ motion and setup error were evaluated simultaneously for 118 individual patients with implanted fiducials and MV electronic portal imaging (EPI). The Gaussian PDF is patient specific and group standard deviation (SD) should not be used for accurate treatment planning for individual patients. Frequent verification imaging should be employed in situations where geometric uncertainties are expected. The dose distribution including geometric uncertainties was determined from integration of the convolution of the static dose gradient with the PDF. Local maximum dose gradient (LMDG) was determined via optimization of dose objective function by manually adjusting DVH control points or selecting beam numbers and directions during IMRT treatment planning. EUDf is a useful QA parameter for interpreting the biological impact of geometric uncertainties on the static dose distribution. The EUDf has been used as the basis for the time-course NTCP evaluation in the thesis. Relative NTCP values are useful for comparative QA checking by normalizing known complications (e.g. reported in the RTOG studies) to specific DVH control points. For prostate cancer patients, rectal complications were evaluated from specific RTOG clinical trials and detailed evaluation of the treatment techniques. Treatment plans that did not meet DVH constraints represented additional complication risk. Geometric uncertainties improved or worsened rectal NTCP depending on individual internal organ motion within patient.

IMRT uses non-uniform beam intensities within a radiation field to provide patient-specific dose shaping, resulting in a dose distribution that conforms tightly to the planning target volume (PTV). Unavoidable geometric uncertainty arising from patient repositioning and internal organ motion can lead to lower conformality index (CI), a decrease in tumor control probability (TCP) and an increase in normal tissue complication probability (NTCP). The CI of the IMRT plan depends heavily on steep dose gradients between the PTV and organ at risk (OAR). Geometric uncertainties reduce the planned dose gradients and result in a less steep or “blurred” dose gradient. The blurred dose gradients can be maximized by constraining the dose objective function in the static IMRT plan or by reducing geometric uncertainty during treatment with corrective verification imaging. Internal organ motion and setup error were evaluated simultaneously for 118 individual patients with implanted fiducials and MV electronic portal imaging (EPI). The Gaussian PDF is patient specific and group standard deviation (SD) should not be used for accurate treatment planning for individual patients. Frequent verification imaging should be employed in situations where geometric uncertainties are expected. The dose distribution including geometric uncertainties was determined from integration of the convolution of the static dose gradient with the PDF. Local maximum dose gradient (LMDG) was determined via optimization of dose objective function by manually adjusting DVH control points or selecting beam numbers and directions during IMRT treatment planning. EUDf is a useful QA parameter for interpreting the biological impact of geometric uncertainties on the static dose distribution. The EUDf has been used as the basis for the time-course NTCP evaluation in the thesis. Relative NTCP values are useful for comparative QA checking by normalizing known complications (e.g. reported in the RTOG studies) to specific DVH control points. For prostate cancer patients, rectal complications were evaluated from specific RTOG clinical trials and detailed evaluation of the treatment techniques. Treatment plans that did not meet DVH constraints represented additional complication risk. Geometric uncertainties improved or worsened rectal NTCP depending on individual internal organ motion within patient.

IMRT uses non-uniform beam intensities within a radiation field to provide patient-specific dose shaping, resulting in a dose distribution that conforms tightly to the planning target volume (PTV). Unavoidable geometric uncertainty arising from patient repositioning and internal organ motion can lead to lower conformality index (CI), a decrease in tumor control probability (TCP) and an increase in normal tissue complication probability (NTCP). The CI of the IMRT plan depends heavily on steep dose gradients between the PTV and organ at risk (OAR). Geometric uncertainties reduce the planned dose gradients and result in a less steep or “blurred” dose gradient. The blurred dose gradients can be maximized by constraining the dose objective function in the static IMRT plan or by reducing geometric uncertainty during treatment with corrective verification imaging. Internal organ motion and setup error were evaluated simultaneously for 118 individual patients with implanted fiducials and MV electronic portal imaging (EPI). The Gaussian PDF is patient specific and group standard deviation (SD) should not be used for accurate treatment planning for individual patients. Frequent verification imaging should be employed in situations where geometric uncertainties are expected. The dose distribution including geometric uncertainties was determined from integration of the convolution of the static dose gradient with the PDF. Local maximum dose gradient (LMDG) was determined via optimization of dose objective function by manually adjusting DVH control points or selecting beam numbers and directions during IMRT treatment planning. EUDf is a useful QA parameter for interpreting the biological impact of geometric uncertainties on the static dose distribution. The EUDf has been used as the basis for the time-course NTCP evaluation in the thesis. Relative NTCP values are useful for comparative QA checking by normalizing known complications (e.g. reported in the RTOG studies) to specific DVH control points. For prostate cancer patients, rectal complications were evaluated from specific RTOG clinical trials and detailed evaluation of the treatment techniques. Treatment plans that did not meet DVH constraints represented additional complication risk. Geometric uncertainties improved or worsened rectal NTCP depending on individual internal organ motion within patient.

Background: Intensity Modulated Radiation Therapy (IMRT) is a method of delivering high-dose radiation to tumours while sparing surrounding healthy tissues. Despite its wide availability IMRT utilization varies across Ontario. The study’s objective was to examine key steps in the implementation process and identify factors that facilitate or impede IMRT implementation. Research Methods: An embedded multiple case study design, utilizing document analysis and key-informant interviews, was employed. Four cancer centres were selected and key-informant interviews were conducted with radiation oncologists, physicists, radiation therapists, and administrators. Results: Eighteen of 21 invited key-informants participated (86% participation rate) providing a range of insights on the factors influencing IMRT implementation. Overall, three cases made progress in the implementation of IMRT, while one case had limited implementation over the same time period. Conclusion: These findings help explain the observed variation in IMRT implementation across Ontario, which is multifaceted and reflects ongoing processes of change and reinvention.

Background: Intensity Modulated Radiation Therapy (IMRT) is a method of delivering high-dose radiation to tumours while sparing surrounding healthy tissues. Despite its wide availability IMRT utilization varies across Ontario. The study’s objective was to examine key steps in the implementation process and identify factors that facilitate or impede IMRT implementation. Research Methods: An embedded multiple case study design, utilizing document analysis and key-informant interviews, was employed. Four cancer centres were selected and key-informant interviews were conducted with radiation oncologists, physicists, radiation therapists, and administrators. Results: Eighteen of 21 invited key-informants participated (86% participation rate) providing a range of insights on the factors influencing IMRT implementation. Overall, three cases made progress in the implementation of IMRT, while one case had limited implementation over the same time period. Conclusion: These findings help explain the observed variation in IMRT implementation across Ontario, which is multifaceted and reflects ongoing processes of change and reinvention.

Nowadays more and more radiotherapy departments use intensity modulated beams for treatment of patients. Intensity modulated radiotherapy (ImRT) is able to modificate intensity of radiation across the iradiated field. In this way it is posible to achieve better dose conformity than in conventional radiotherapy. Implementation of ImRT allows us to escalate dose to target volume with same side effects of organs at risk as in conventional radiotherapy or to reduce normal tissue complication - decrease dose to organ at risk with the same tumour dose. This fact reguires extension of our guality system to all network of delivery dose to patients, inclusive linear accelerator with multileaf collimator, treatment planning system, electronic portal imaging device and so on. Quality assurance is guaranteed both periodical user tests and independent verification of The State Office for Nuclear Safety. The aim of this work is finding the optimal and effective way for the verification treatment plans, determining criteria for evaluation measured results, proposing summary all aspects of radiation protection patients which are treate ionisation beams with intensity modulated radiotherapy. The optimization one of the principles of radiation protection will be provided by routin verification treatment plans.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第14579号 / 工博第3047号 / 新制||工||1454(附属図書館) / 26931 / UT51-2009-D291 / 京都大学大学院工学研究科電子工学専攻 / (主査)教授 石川 順三, 教授 髙岡 義寛, 教授 小林 哲生 / 学位規則第4条第1項該当