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Authors
Advisor(s)
Abstract(s)
A radioterapia é uma das modalidades mais usadas para o tratamento do cancro
da próstata, apresentando bons resultados quer em termos de controlo tumoral, quer em
termos de sobrevida livre de doença. No entanto, pacientes portadores de próteses
femorais representam um desafio para a radioterapia.
Numa primeira fase, a prótese metálica gera artefacto nas imagens de TC que
servem de base para o planeamento do tratamento de radioterapia. Nesse sentido, os
scanners de TC devem ser portadores de uma profundidade de bits abrangente para a
variação de densidade dos materiais presentes na imagem. As definições do equipamento
aliadas a uma curva de calibração adequada permitem gerar imagens com mais qualidade
e definição, cujos voxeis apresentam valores de densidade fidedignos.
Estas estratégias suportam uma correta delineação de volumes e o cálculo da
distribuição de dose, que é objeto do presente estudo.
Para o cálculo da distribuição de dose na presença de materiais de alta densidade,
é necessária a aplicação de um algoritmo de cálculo que contabilize todas interações da
radiação com a matéria.
Este trabalho consistiu na avaliação da distribuição de dose de um tratamento de
radioterapia para o cancro da próstata em um paciente com prótese femoral.
Para essa avaliação, foram testados três materiais de diferentes densidades,
aplicados no formato de próteses sólidas, ocas ou combinação de materiais.
O paciente alvo do estudo não possuía prótese femoral, de forma a reduzir
imprecisões associadas ao artefacto gerado pelo implante, pelo que as densidades dos
materiais da prótese foram impostas manualmente.
Foram desenvolvidos dois planos de tratamento, aplicados ao paciente em estudo
e os mesmos planos simulados para o esse paciente na presença de diferentes próteses
femorais. Um dos planos consistiu numa irradiação ao longo de 360°, enquanto o plano
alternativo possuía uma secção de bloqueio de irradiação, com o intuito de evitar a
irradiação direta da prótese.
Das simulações geradas foi avaliado o prejuízo em termos de cobertura do
volume alvo, bem como o impacto na dose recebida pelas estruturas saudáveis
circundantes.
Adicionalmente ao foco deste estudo foi feita uma simulação do comportamento
da radiação na interface tecido-implante, através de um campo direto à prótese femoral.
Para esta avaliação foram definidos três pontos anteriores à prótese e três pontos
posteriores, nos quais foi registada a dose detetada
Radiotherapy is one of the modalities more frequently used to treat the prostate cancer, showing good results as tumor control, but also as free survival lifetime. Nonetheless, patients carrying femoral prothesis represents a challenge for radiotherapy. In a first approach, metallic prothesis produce artefacts on CT images that are the base for a radiotherapy treatment planning. According to that, the CT scanner must be carrier of a comprehensive bit depth to the variation of materials density, presents in the image. The definitions of the equipment associated with a proper calibration curve, allows generate images with more quality and definition, whose voxels present density values reliable. These strategies support a correct volumes delineation and the dose distribution calculation, which is the object of the present study. To calculate the dose distribution in the presence of highly dense materials, it is necessary to apply a calculation algorithm the take into account all the interactions of the radiation with the material. This work consisted of the evaluation of dose distribution of a radiotherapy treatment for prostate cancer, in a patient wearing a femoral prothesis. To this evaluation, three different density materials were tested, in the form of solid prothesis, hollow or combining materials. The target patient of this study didn’t have a femoral prothesis, to reduce the imprecisions associated to the artefact produced by the metallic implant, so the material densities were imposed manually. Two treatment plans were developed, applied to the same patient, in the presence of different kind of prothesis. One of the plans were composed by a 360° degree irradiation, while the second one had a lock section, avoid the prothesis direct irradiation. From de produced simulations, it was accessed de target cover prejudice and the dose received by the healthy structures. Additionally, it was simulated the radiation behavior in the tissue-implant interface, through a straight beam to the femoral prothesis. For this evaluation three points before the prothesis and three points in the back were defined and the detected dose recorded
Radiotherapy is one of the modalities more frequently used to treat the prostate cancer, showing good results as tumor control, but also as free survival lifetime. Nonetheless, patients carrying femoral prothesis represents a challenge for radiotherapy. In a first approach, metallic prothesis produce artefacts on CT images that are the base for a radiotherapy treatment planning. According to that, the CT scanner must be carrier of a comprehensive bit depth to the variation of materials density, presents in the image. The definitions of the equipment associated with a proper calibration curve, allows generate images with more quality and definition, whose voxels present density values reliable. These strategies support a correct volumes delineation and the dose distribution calculation, which is the object of the present study. To calculate the dose distribution in the presence of highly dense materials, it is necessary to apply a calculation algorithm the take into account all the interactions of the radiation with the material. This work consisted of the evaluation of dose distribution of a radiotherapy treatment for prostate cancer, in a patient wearing a femoral prothesis. To this evaluation, three different density materials were tested, in the form of solid prothesis, hollow or combining materials. The target patient of this study didn’t have a femoral prothesis, to reduce the imprecisions associated to the artefact produced by the metallic implant, so the material densities were imposed manually. Two treatment plans were developed, applied to the same patient, in the presence of different kind of prothesis. One of the plans were composed by a 360° degree irradiation, while the second one had a lock section, avoid the prothesis direct irradiation. From de produced simulations, it was accessed de target cover prejudice and the dose received by the healthy structures. Additionally, it was simulated the radiation behavior in the tissue-implant interface, through a straight beam to the femoral prothesis. For this evaluation three points before the prothesis and three points in the back were defined and the detected dose recorded
Description
Keywords
Artroplastia da anca Cancro da próstata Prótese Radioterapia Hip arthroplasty Prostate cancer Prothesis Radiotherapy