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Authors
Advisor(s)
Abstract(s)
O tratamento primordial atual para o cancro cervical localmente avançado é uma
combinação de Radioterapia Externa (RTE), Braquiterapia (BT) e Quimioterapia. A
GEC-ESTRO criou várias recomendações para a prática deste tipo de tratamentos, sendo
uma delas a forma como deve ser calculada a dose entregue aos Órgãos em Risco (OARs)
em tratamentos de radiação. Esta recomendação indica que se faça uma adição direta da
dose prescrita na RTE e dos parâmetros dos Histogramas de Dose-Volume (DVH) das
frações de BT. No entanto, esta adição direta pode sobrestimar as doses cumulativas
quando os hotspots não se sobrepõem entre frações. Tendo em conta que esta assunção
genérica não é suficientemente precisa na realidade, estudou-se, no presente trabalho, a
possibilidade de utilizar o registo deformável entre imagens de planeamento dos
tratamentos, para posteriormente somar localmente, voxel a voxel, as doses de radiação.
Para executar o registo deformável e calcular os parâmetros dos DVHs utilizou-se o
software 3D Slicer. Foi criado um script em Python para transformar as matrizes de dose,
voxel a voxel, num formato de dose comparável entre técnicas distintas (EQD2) de
radioterapia. Para validar a eficácia dos registos deformáveis utilizou-se o Coeficiente
Dice, sendo que se obteve uma média de 0.66 para a bexiga e de 0.57 para o reto. Os
resultados obtidos da dose acumulada dão a entender que, sem registo das imagens, o
método tradicional tende a sobrestimar a dose acumulada para a bexiga e a subestimar a
dose acumulada para o reto.
The current primary treatment for locally advanced cervical cancer is a combination of External Beam Radiotherapy (EBRT), Brachytherapy (BT) and Chemotherapy. GEC-ESTRO has created several recommendations for the practice of this type of treatment, one of which is how the dose delivered to Organs at Risk (OARs) in radiation treatments should be calculated. This recommendation indicates that a direct addition should be made of the dose prescribed in the EBRT and the parameters of the Dose-Volume Histograms (DVH) of the BT fractions. However, this direct addition may overestimate cumulative doses when hotspots do not overlap between fractions. Bearing in mind that this generic assumption is not sufficiently accurate in reality, this study investigated the possibility of using deformable registration between treatment planning images, to subsequently sum the radiation doses locally, voxel by voxel. The 3D Slicer software was used to perform the deformable registration and calculate the DVH parameters. A Python script was created to transform the dose matrices, voxel by voxel, into a dose format comparable between different radiotherapy techniques (EQD2). The Dice Coefficient was used to validate the accuracy of the deformable registrations, obtaining an average of 0.66 for the bladder and 0.57 for the rectum. The results obtained for the accumulated dose suggest that, without image registration, the traditional method tends to overestimate the accumulated dose to the bladder and underestimate the accumulated dose to the rectum.
The current primary treatment for locally advanced cervical cancer is a combination of External Beam Radiotherapy (EBRT), Brachytherapy (BT) and Chemotherapy. GEC-ESTRO has created several recommendations for the practice of this type of treatment, one of which is how the dose delivered to Organs at Risk (OARs) in radiation treatments should be calculated. This recommendation indicates that a direct addition should be made of the dose prescribed in the EBRT and the parameters of the Dose-Volume Histograms (DVH) of the BT fractions. However, this direct addition may overestimate cumulative doses when hotspots do not overlap between fractions. Bearing in mind that this generic assumption is not sufficiently accurate in reality, this study investigated the possibility of using deformable registration between treatment planning images, to subsequently sum the radiation doses locally, voxel by voxel. The 3D Slicer software was used to perform the deformable registration and calculate the DVH parameters. A Python script was created to transform the dose matrices, voxel by voxel, into a dose format comparable between different radiotherapy techniques (EQD2). The Dice Coefficient was used to validate the accuracy of the deformable registrations, obtaining an average of 0.66 for the bladder and 0.57 for the rectum. The results obtained for the accumulated dose suggest that, without image registration, the traditional method tends to overestimate the accumulated dose to the bladder and underestimate the accumulated dose to the rectum.
Description
Keywords
External Beam Radiotherapy Brachytherapy Equivalent Dose Dose-Volume Histograms 3D Slicer