A braquiterapia é a modalidade de tratamento radioterápico que utiliza fontes radioativas seladas a uma distância curta do tumor, diminuindo o risco de aplicação de uma dose indesejável em tecidos sadios adjacentes. Para que a braquiterapia seja confiável, é necessário estabelecer um programa de práticas dosimétricas visando a determinação da dose ideal de radiação para esta prática radioterápica. Neste trabalho apresenta a aplicação de duas metodologias destinadas à dosimetria utilizando filmes radiocrômicos. Medidas experimentais foram realizadas com filmes EBT3 em objetos simuladores composto de material homogêneo e heterogêneo (pulmão, osso e tecidos moles) construídos especialmente para medidas de dose em braquiterapia. Os processamentos e analises das imagens resultantes do procedimento experimental foram realizados com o software IMAGEJ e MATLAB. Os resultados foram avaliados a partir de comparações medidas experimentais de dose e obtidas por simulações pelo Método de Monte Carlo. / Brachytherapy is a radiotherapy treatment modality using radioactive sealed sources within walking distance of the tumor, reducing the risk of applying an unwanted dose to adjacent healthy tissues. For brachytherapy is reliable, it is necessary to establish a dosimetric practices program aimed at determining the optimal dose of radiation for this radiotherapy practice. This paper presents the application of two methodologies for the dosimetry using radiochromic movies. Experimental measurements were performed with EBT3 movies phantoms consisting of homogeneous and heterogeneous material (lung, bone and soft tissue) built especially for dose measurements in brachytherapy. The processing and analysis of the resulting images of the experimental procedure were performed with ImageJ software and MATLAB. The results were evaluated from comparisons dose of experimental measurements and simulations obtained by the Monte Carlo method.

O sucesso do tratamento de neoplasias depende da precisão na localização tumoral e de áreas críticas limítrofes, e da distribuição da dose entregue a esses volumes. O objetivo deste trabalho foi verificar a utilização do filme radiocrômico Gafchromic R EBT2 na avaliação da distribuição de dose em planejamentos radioterápicos, desenvolvendo um protocolo dosimétrico capaz de verificar a conformidade entre distribuições de doses planejada e entregue em teleterapia. Avaliou-se também, a contribuição da separação dos canais RGB das imagens para o controle da qualidade dos planejamentos utilizando esses filmes. Com esse intuito, realizou-se testes para verificação das características do filme EBT2 e do digitalizador a fim de obter-se um protocolo dosimétrico adequado. Realizou-se a simulação de tratamentos de sistema nervoso central com a irradiação de um objeto simulador homogêneo, com 5 campos em um acelerador linear de 6 MV e comparou-se com os dados do sistema de planejamento através de mapas de índice gama. Observou-se que o canal verde, apresenta maior conformidade aos valores de referência. Os mapas de índice gama, resultaram em uma conformação de 98% para critérios de aceitação de DD = 3 % e DTA = 3 mm, de acordo com os limites estabelecidos no Report 62 do ICRU. Ao final deste trabalho, concluiu-se que o protocolo estabelecido com a análise do canal verde no filme EBT2 é adequado para a realização do controle da qualidade em tratamentos conformacionais, sendo uma ferramenta de fácil implementação para avaliação da distribuição de dose nesses tratamentos. / The successful treatment of neoplasms depends on the accurate localization of the tumor and adjacent critical areas, and the distribution of the dose delivered to these volumes. The objective of this work was to verify the use of radiochromic film Gafchromic R EBT2 to evaluate the dose distribution in radiotherapy planning, developing a dosimetric protocol able to check the conformity between the planned and delivered dose distributions in teletherapy. The contribution of the RGB channel separation in the images to quality control of the planning was also evaluated. With this purpose, EBT2 film was calibrated and studied to verify its characteristics when read with a scanner in order to obtain a suitable dosimetric protocol. Simulation in a homogeneous phantom with 5 radiation fields on a 6 MV linear accelerator was compared with the planning system data through gamma index maps. It was observed that the green channel has a higher conformity with the reference values. The gamma index maps resulted in a conformation of 98% when the acceptance criteria was DD = 3% and DTA = 3 mm, according to the limits established by the ICRU Report 62. This study concluded that the protocol established for the analysis EBT2 films with green channel is suitable for performing quality control in conformational treatments.

<p>Interventional radiological procedures often require long fluoroscopic exposure times and high levels of radiation exposure to patients, which often are higher than most radiological examinations except for computed tomography (CT) whose effective doses can be higher, and in addition to having radiation risks that are higher for both patient and medical staff. Therefore it is important to monitor and map the radiation entrance exposure to the patients, to minimize the probability of skin injury, and to detect areas of overlapping radiation fields. The aim of this thesis is to evaluate patient doses in interventional radiology procedures using a new GAFCHROMIC-XR TYPE R DOSIMETER MEDIA X-ray Dosimetry film, which allows mapping of the skin dose distribution, when placed closer to the skin. These radiochromic films can be characterized by a power response dose function when plotting pixel value versus air kerma and have been calibrated up to 5 Gy when using a flatbed scanner. Image analysis was performed using the red channel component of standard the RGB (Red, Green, and Blue) color space image. The association between the Maximum Entrance Skin Doses (MESD) and Dose Area Product (DAP) values for two interventional procedures; coronary angiography (CA), and percutaneous transluminal coronary angiography (PTCA) is investigated.</p>

Interventional radiological procedures often require long fluoroscopic exposure times and high levels of radiation exposure to patients, which often are higher than most radiological examinations except for computed tomography (CT) whose effective doses can be higher, and in addition to having radiation risks that are higher for both patient and medical staff. Therefore it is important to monitor and map the radiation entrance exposure to the patients, to minimize the probability of skin injury, and to detect areas of overlapping radiation fields. The aim of this thesis is to evaluate patient doses in interventional radiology procedures using a new GAFCHROMIC-XR TYPE R DOSIMETER MEDIA X-ray Dosimetry film, which allows mapping of the skin dose distribution, when placed closer to the skin. These radiochromic films can be characterized by a power response dose function when plotting pixel value versus air kerma and have been calibrated up to 5 Gy when using a flatbed scanner. Image analysis was performed using the red channel component of standard the RGB (Red, Green, and Blue) color space image. The association between the Maximum Entrance Skin Doses (MESD) and Dose Area Product (DAP) values for two interventional procedures; coronary angiography (CA), and percutaneous transluminal coronary angiography (PTCA) is investigated.

Purpose: To examine the dosimetric characteristics of Gafchromic EBT3 film when measuring small fields of radiation, and compare it against other common radiation detectors. Methods and Materials: EBT3 film was placed in a solid water phantom and irradiated with 6MV photons, field sizes from 10x10cm2 down to 6x6mm2. The films were scanned with a Vidar DosimetryPRO Advantage Red scanner, and analyzed with RIT113 software. The films were also scanned at different orientations and times to quantify the discrepancies associated with scanning orientation and post-exposure darkening. The same fields were measured with a PTW TN30013 farmer chamber, an Exradin T1 cylindrical ion chamber, a PTW parallel plate ion chamber, and a Sun Nuclear Edge Detector (diode). Output factors were calculated for each detector and compared for accuracy. The output factors were measured from a Varian Clinac iX, Clinac 21EX, Trilogy, and TrueBeam; as well as a Novalis Tx. The outputs from different machines at different clinics were compared. Results: The EBT3 film and Edge Detector were the only detectors that succeeded in accurately measuring the output from all field sizes; the ion chambers were too large and failed for field sizes below 4x4cm2 due to volume averaging. The dose measured with the film increased by an average of 8.8% after one week post-irradiation. The dose measured was also reduced by an average of 4.4% by scanning the film in landscape orientation, as opposed to portrait orientation. It was shown that the output factors for the smallest field of 6x6mm2--successfully measured with film and diode--varied between 0.54-0.74 for five different machines at three different clinics. Conclusions: The feasibility of using Gafchromic EBT3 film to measure very small fields of radiation is confirmed. Of the other 4 detectors used, only the diode was shown to be capable of accurately measuring small fields of radiation. The need to optimize the film dosimetry process--including the time films are scanned post-irradiation, the consistency of the scanning orientation of the calibration and subsequent films, and the measurement procedure on the computer software--is highlighted.

A braquiterapia é a modalidade de tratamento radioterápico que utiliza fontes radioativas seladas a uma distância curta do tumor, diminuindo o risco de aplicação de uma dose indesejável em tecidos sadios adjacentes. Para que a braquiterapia seja confiável, é necessário estabelecer um programa de práticas dosimétricas visando a determinação da dose ideal de radiação para esta prática radioterápica. Neste trabalho apresenta a aplicação de duas metodologias destinadas à dosimetria utilizando filmes radiocrômicos. Medidas experimentais foram realizadas com filmes EBT3 em objetos simuladores composto de material homogêneo e heterogêneo (pulmão, osso e tecidos moles) construídos especialmente para medidas de dose em braquiterapia. Os processamentos e analises das imagens resultantes do procedimento experimental foram realizados com o software IMAGEJ e MATLAB. Os resultados foram avaliados a partir de comparações medidas experimentais de dose e obtidas por simulações pelo Método de Monte Carlo. / Brachytherapy is a radiotherapy treatment modality using radioactive sealed sources within walking distance of the tumor, reducing the risk of applying an unwanted dose to adjacent healthy tissues. For brachytherapy is reliable, it is necessary to establish a dosimetric practices program aimed at determining the optimal dose of radiation for this radiotherapy practice. This paper presents the application of two methodologies for the dosimetry using radiochromic movies. Experimental measurements were performed with EBT3 movies phantoms consisting of homogeneous and heterogeneous material (lung, bone and soft tissue) built especially for dose measurements in brachytherapy. The processing and analysis of the resulting images of the experimental procedure were performed with ImageJ software and MATLAB. The results were evaluated from comparisons dose of experimental measurements and simulations obtained by the Monte Carlo method.

O sucesso do tratamento de neoplasias depende da precisão na localização tumoral e de áreas críticas limítrofes, e da distribuição da dose entregue a esses volumes. O objetivo deste trabalho foi verificar a utilização do filme radiocrômico Gafchromic R EBT2 na avaliação da distribuição de dose em planejamentos radioterápicos, desenvolvendo um protocolo dosimétrico capaz de verificar a conformidade entre distribuições de doses planejada e entregue em teleterapia. Avaliou-se também, a contribuição da separação dos canais RGB das imagens para o controle da qualidade dos planejamentos utilizando esses filmes. Com esse intuito, realizou-se testes para verificação das características do filme EBT2 e do digitalizador a fim de obter-se um protocolo dosimétrico adequado. Realizou-se a simulação de tratamentos de sistema nervoso central com a irradiação de um objeto simulador homogêneo, com 5 campos em um acelerador linear de 6 MV e comparou-se com os dados do sistema de planejamento através de mapas de índice gama. Observou-se que o canal verde, apresenta maior conformidade aos valores de referência. Os mapas de índice gama, resultaram em uma conformação de 98% para critérios de aceitação de DD = 3 % e DTA = 3 mm, de acordo com os limites estabelecidos no Report 62 do ICRU. Ao final deste trabalho, concluiu-se que o protocolo estabelecido com a análise do canal verde no filme EBT2 é adequado para a realização do controle da qualidade em tratamentos conformacionais, sendo uma ferramenta de fácil implementação para avaliação da distribuição de dose nesses tratamentos. / The successful treatment of neoplasms depends on the accurate localization of the tumor and adjacent critical areas, and the distribution of the dose delivered to these volumes. The objective of this work was to verify the use of radiochromic film Gafchromic R EBT2 to evaluate the dose distribution in radiotherapy planning, developing a dosimetric protocol able to check the conformity between the planned and delivered dose distributions in teletherapy. The contribution of the RGB channel separation in the images to quality control of the planning was also evaluated. With this purpose, EBT2 film was calibrated and studied to verify its characteristics when read with a scanner in order to obtain a suitable dosimetric protocol. Simulation in a homogeneous phantom with 5 radiation fields on a 6 MV linear accelerator was compared with the planning system data through gamma index maps. It was observed that the green channel has a higher conformity with the reference values. The gamma index maps resulted in a conformation of 98% when the acceptance criteria was DD = 3% and DTA = 3 mm, according to the limits established by the ICRU Report 62. This study concluded that the protocol established for the analysis EBT2 films with green channel is suitable for performing quality control in conformational treatments.

In radiation therapy, gel dosimetry is used to measure radiation doses for treatment verification. Gel dosimeters have the ability to record dose information in three dimensions. The objective of this thesis was to fabricate a transparent cryogel radiochromic dosimeter with poly(vinyl alcohol) (PVA) as the gelling agent. A transparent dosimeter may be analyzed using an optical read out technique, which is desirable. PVA cryogels can be made transparent by adding dimethyl sulfoxide (DMSO). Measurements of dose response were performed and various parameters were adjusted, including: numbers of freeze-thaw cycles (FTCs); concentrations of PVA; DMSO concentration. The measured absorption coefficient increased linearly with dose up to approximately 10 Gy. The sensitivity was increased for higher PVA concentrations, larger numbers of FTCs, and less DMSO. The resulting dosimeter was stable and showed no significant dose rate or photon energy dependence. The cryogels were later formed into 5 mm thick films and used as a tool for performing in vivo dosimetry. The dose response of the radiochromic bolus was characterized by irradiating it on a flat surface at different gantry angles. The dose measured in the bolus was approximately 0.80 of the dose measured by Gafchromic film at the skin surface, taking the obliquity into account. IMRT treatments were delivered to a RANDO phantom. The radiochromic bolus was used to measure skin surface dose in two dimensions at various locations. The 0.80 factor was used to calibrate the bolus, which was then compared to an accompanying film measurement. Good agreement was observed between the measurements (>95% gamma pass rate), suggesting the radiochromic bolus may be suitable for in vivo applications. The radiochromic bolus was then used to evaluate errors associated with the breath hold technique often used with left chest wall tangential irradiation. Treatment plan incorporating the radiochromic bolus was delivered at the planned position and shifted anterior-posteriorly (A/P) up to 5 mm. Large discrepancies from the planned two dimensional skin surface distribution were observed for shifts as small as 3 mm in the A/P direction. The study demonstrated that the cryogel was sensitive to small positioning uncertainties for chest wall irradiations, potentially allowing for the detection of clinically relevant errors. Other potential formulations of PVA-based radiochromic cryogels are discussed briefly as avenues to future research projects. / Thesis / Doctor of Philosophy (PhD)

This research aims to develop a tissue-mimicking material and produce a 3D gelatin that has density of approximately a human lung, which is in the ranges of (0.25 – 0.35) g/cm3. Tissue equivalent models are important in order to study the radiation dose planned for patients. To achieve the desired density of a human tissue, different types of gelatin were whisked for 300 seconds using a typical hand mixer. The mechanical properties of the gelatin mixtures, standard and foamed, were evaluated by applying different forces. The mechanical properties for the gels were measured using an indentation technique, which showed that the gels act as elastic materials. The mechanical properties of the foams were also evaluated. Mixtures that contained 300 bloom gelatin, glycerol, and sorbitol, were whisked for 60, 180, 300 seconds to achieve different densities evaluated by CT imaging. The density of the180 - and 300 - seconds gelatin foams were found to be 0.33 ± 0.16 and 0.33  0.052 g/cm3, respectively, which is similar to the human lung density. Finally, FXO gel sheets and the FXO foam sheets were irradiated and the radiosensitivity quantified by measuring transmission using a spectrometer. The change in the attenuation coefficient was linear with dose. / Thesis / Master of Science (MSc)

Ces dernières années, les techniques de traitement des cancers par radiothérapie externe se sont complexifiéesafin de cibler la tumeur tout en protégeant les organes à risque. Les systèmes de planification de traitement (TPS)réalisent un calcul prévisionnel de la distribution de la dose absorbée dans le patient (via des images CT).Afin d’obtenir un résultat de dose précis dans un temps raisonnable, le calcul est effectué par des algorithmessimplifiés. En présence de dispositifs médicaux métalliques de masses volumiques élevées (prothèses de hancheou prothèses dentaires), les algorithmes atteignent leurs limites. De plus, ces dispositifs perturbent lareconstruction tomodensitométrique en créant des artéfacts sur les images rendant difficile la délinéation desorganes. L’objectif de ce travail a été d’évaluer les algorithmes implémentés dans les TPS en présenced’hétérogénéités de forte densité avec des mesures expérimentales et le code de calcul Monte-Carlo BEAMnrcdans un fantôme anthropomorphique tout d’abord avec des échantillons naturels, puis avec des échantillonscalibrés. Ensuite, une évaluation rétrospective des algorithmes cliniques par rapport à Monte-Carlo a été réaliséeavec des patients traités en RC3D et en RCMI.Les mesures ont mis en évidence une atténuation pouvant aller jusqu’à 17 % pour l’amalgame dentaire parrapport à l’algorithme clinique sur les images CT avec artéfacts, créant une zone de sous-dosage dans le volumecible. L’ensemble des résultats a donné lieu à des recommandations pour la clinique (corriger les images CT si levolume cible est à moins de 3 cm d’une prothèse, privilégier l’algorithme AAA plutôt que Pencil Beam…). / The last few years, cancer treatment techniques in radiation therapy have become more complex to better targetthe tumor while protecting the organs at risk. The treatment planning systems (TPS) achieve a predictivecalculation of the distribution of the dose absorbed by the patient (via CT images).In order to obtain an accurate dose result within a reasonable time, the calculation is performed with simplifiedalgorithms. In the presence of medical devices made of high density metal (hip prosthesis or dental prosthesis),the algorithms reach their limits. Moreover, these devices disrupt computed tomography reconstruction, creatingartifacts on the images and thus making difficult the delineation of organs. The aim of this work is to evaluatethe algorithms of the TPS in the presence of high density heterogeneity using experimental measurements andthe Monte Carlo BEAMnrc code in an anthropomorphic phantom: on one hand with natural samples, and on theother hand, with calibrated samples. Then, a retrospective evaluation of clinical algorithms compared to MonteCarlo is achieved using treated patients in Conformal Radiotherapy and in Intensity Modulated RadiationTherapy (IMRT). The measurements show an attenuation of up to 17 % for dental amalgam compared with theclinical algorithm on CT images with artifacts, creating an under-dosage area in the target volume. All theseresults lead to recommendations for the clinical treatments (corrected CT images if the target volume is closerthan 3 cm to prosthesis, favor the AAA algorithm rather than Pencil Beam …).