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Orientador(es)
Resumo(s)
A radiocirurgia estereotáxica (SRS) realizada em tumores intracranianos consiste num procedimento não cirúrgico utilizado como alternativa à cirurgia convencional onde são administradas altas doses de radiação no tumor, em uma única fração, atingindo um elevado gradiente de dose fora da zona alvo. A Gamma Knife (GK) consiste num equipamento médico desenvolvido para realizar SRS em tumores intracranianos. Esta técnica utiliza feixes convergentes, provenientes de um grande número de fontes de Cobalto-60, extremamente colimados, para administrar uma elevada dose de radiação num alvo localizado do cérebro definido através da realização de imagens como a ressonância magnética (RM). O seu principal objetivo é atingir uma elevada taxa de controlo tumoral a longo prazo, mantendo a condição física do paciente, ao mesmo tempo que se diminui a possibilidade de novos tratamentos relacionados com a morbilidade provocada pela radiação. A realização deste trabalho foca-se essencialmente na comparação dos resultados de simulações realizadas com o programa PENetration and Energy LOss of Positrons and Electrons (PENELOPE), com especial enfoque na energia depositada, para dois fantomas computacionais diferentes. Os dois fantomas computacionais foram realizados com o objetivo de avaliar as possíveis diferenças resultantes na prática clínica ao aplicar diferentes algoritmos de dose, tentando reproduzir e comparar os algoritmos que modelam a cabeça humana como um meio homogéneo com os algoritmos que têm em conta as heterogeneidades. O primeiro fantoma foi realizado com o objetivo de representar um algoritmo de dose mais simples que modela toda a cabeça de um paciente como água, é constituído por 2 corpos apenas e foi por isso denominado fantoma simplificado. Já o segundo fantoma realizado, fantoma real, permite ter em consideração as heterogeneidades dos diferentes tecidos presentes na cabeça do paciente e foi realizado com o objetivo de efetuar simulações com um fantoma que represente a cabeça humana de uma forma o mais realista possível. Cada um destes fantomas foi utilizado para a realização de várias simulações, para as quais foi necessária a sua alteração e a aplicação de uma translação ao tumor realizada de maneira a perceber quais seriam os efeitos desta alteração nos resultados. Os resultados das simulações realizadas são comparados, não só entre si, mas também com os resultados encontrados na literatura presente para a realização deste trabalho. A comparação dos resultados para os diferentes fantomas demonstra uma subestimação da dose, por vezes superior a 5%, em simulações realizadas com o fantoma heterogéneo, quando comparadas com os resultados obtidos com o fantoma homogéneo. Estes resultados vão de encontro aos apresentados na literatura como se verifica nos estudos apresentados.
ABSTRACT - Stereotactical radiosurgery (SRS) for intracranial tumors is a non-surgical procedure used as an alternative to conventional surgery where high doses of radiation are delivered to the tumor in a single fraction, reaching a high dose gradient outside the target area. The Gamma Knife (GK) is medical equipment developed to perform SRS on intracranial tumors. This technique uses convergent beams from a large number of extremely collimated Cobalt-60 sources, to deliver a high dose of radiation to a localized target on the brain defined by, for instance, magnetic resonance (RM) imaging. Its main goal is to achieve a high rate of long-term tumor control, maintaining the patient´s physical condition, while decreasing the possibility of further treatments related to radiation morbidity. This work focuses essentially on comparing the results of simulations performed with the PENetration and Energy LOss of Positrons and Electrons (PENELOPE) program, with a special focus on the deposited energy, for two different computational phantoms. The two computational phantoms were created to evaluate possible differences in clinical practice by applying different dose algorithms, trying to reproduce and compare the algorithms that model the human head as a homogenous medium with the algorithms that take into account heterogeneities. The first phantom was realized in order to represent a simpler dose algorithm that models a patient’s entire head like water, it consists of two bodies only and was therefore named simplified phantom. The second phantom, called real phantom, allows to take into consideration the heterogeneities of the different tissues present in the patient’s head and was used with the aim of performing simulations with a phantom that represents the human head in the most realistic way possible. Each of these phantoms was used to perform various simulations, for which it was necessary its modification and application of a translation, performed in order to understand what would be the effects of this change on the results. The results of the simulations performed are compared, not only with each other but also with the results found in the literature. The comparison of the results for the different phantoms demonstrates an under dosage, sometimes greater than 5%, in simulations performed with the heterogeneous phantom when compared with the results obtained with the homogenous phantom. These results are in agreement with those presented in the literature as verified in the presented studies.
ABSTRACT - Stereotactical radiosurgery (SRS) for intracranial tumors is a non-surgical procedure used as an alternative to conventional surgery where high doses of radiation are delivered to the tumor in a single fraction, reaching a high dose gradient outside the target area. The Gamma Knife (GK) is medical equipment developed to perform SRS on intracranial tumors. This technique uses convergent beams from a large number of extremely collimated Cobalt-60 sources, to deliver a high dose of radiation to a localized target on the brain defined by, for instance, magnetic resonance (RM) imaging. Its main goal is to achieve a high rate of long-term tumor control, maintaining the patient´s physical condition, while decreasing the possibility of further treatments related to radiation morbidity. This work focuses essentially on comparing the results of simulations performed with the PENetration and Energy LOss of Positrons and Electrons (PENELOPE) program, with a special focus on the deposited energy, for two different computational phantoms. The two computational phantoms were created to evaluate possible differences in clinical practice by applying different dose algorithms, trying to reproduce and compare the algorithms that model the human head as a homogenous medium with the algorithms that take into account heterogeneities. The first phantom was realized in order to represent a simpler dose algorithm that models a patient’s entire head like water, it consists of two bodies only and was therefore named simplified phantom. The second phantom, called real phantom, allows to take into consideration the heterogeneities of the different tissues present in the patient’s head and was used with the aim of performing simulations with a phantom that represents the human head in the most realistic way possible. Each of these phantoms was used to perform various simulations, for which it was necessary its modification and application of a translation, performed in order to understand what would be the effects of this change on the results. The results of the simulations performed are compared, not only with each other but also with the results found in the literature. The comparison of the results for the different phantoms demonstrates an under dosage, sometimes greater than 5%, in simulations performed with the heterogeneous phantom when compared with the results obtained with the homogenous phantom. These results are in agreement with those presented in the literature as verified in the presented studies.
Descrição
Mestrado em Engenharia Biomédica
Palavras-chave
Radiocirurgia estereotáxica Tumor intracraniano Energia depositada Stereotactical radiosurgery Intracranial tumor Gamma knife perfexion PFX PENetration and Energy LOss of Positrons and Electrons PENELOPE Deposited energy
Contexto Educativo
Citação
Fernandes TF. Estudos de cálculos dosimétricos em tratamentos com o equipamento Gamma Knife [dissertation]. Lisboa: Escola Superior de Tecnologia da Saúde de Lisboa - Instituto Superior de Engenharia de Lisboa/Instituto Politécnico de Lisboa; 2019.
Editora
Instituto Politécnico de Lisboa, Escola Superior de Tecnologia da Saúde de Lisboa