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Estudo da Influência de Desvios Posicionais na Dose Administrada em Órgãos de Risco em Tratamentos de Radioterapia
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Tratamento oncológico por radioterapia é uma prática de extrema importância, mas
também requer muito cuidado, exigindo um elevado grau de precisão. O paciente será
exposto a radiação ionizante com o intuito de eliminar tumores, processo durante o qual
a sua segurança tem de estar garantida e, para tal, entre outros aspetos, é necessário
assegurar que o seu posicionamento em relação ao ponto de referência se encontra de
acordo com o esperado. Caso isto não se verifique, a distribuição de dose calculada no
planeamento pode estar comprometida. Pretende-se maximizar a cobertura do tumor
quando se está a irradiar o paciente, mas este estará perto de outros tecidos e órgãos
de risco que têm de ser protegidos, e é necessário encontrar este equilíbrio. Se existirem
desvios na posição do doente, corre-se o risco que a dose passe a cobrir mais destes
órgãos de risco do que devido, e isto pode acarretar sérias consequências. No entanto, é
impossível colocar o paciente sempre exatamente na mesma posição, desvios posicionais
vão sempre acontecer, por mais reduzidos que sejam. Dado à sua dimensão, são difíceis
tanto de detetar como de avaliar em termos de gravidade.
Deste modo, esta dissertação estudou a influência dos desvios posicionais na dose
administrada em órgãos específicos de risco, reto e medula. Para tal, foram simulados,
em vários casos de pacientes de ambas as patologias, desvios em diferentes direções
movendo-se o Isocentro da irradiação, com o objetivo de analisar o seu impacto no cálculo
e distribuição da dose.
Com isto, pôde-se concluir que a segurança do reto é comprometida para desvios de
pelo menos -0,7 cm no eixo z, sendo relevante corrigir a posição do paciente a partir deste
ponto, trazendo este um risco de lesão de grau mínimo 2 de até 19 % e de grau mínimo
3 de até 3 %. No caso da medula, concluiu-se que o paciente deve ser reposicionado em
desvios no eixo z de cerca de -0,8 cm, sendo o seu risco de de mielopatia 6 %. Desvios que
cheguem a -1,0 cm em z já apresentam um risco de 50 %.
Radiotherapy oncology treatment is an extremely important practice, but at the same time it demands a lot of carefulness, demanding a high degree of precision. A patient will be exposed to ionizing radiation with the purpose of eliminating tumors, but their safety must be garanteed and, for that, amongst other factors, it is necessary to ensure that their physical position in relation to the reference point is according to what is expected. Should this not be the case, the dose distribution of the treatment could be compromised. The intention is to maximize tumor coverage while patient irradiation is occurring, but said tumor will be in the proximity of organs of risk that must be protected, and it is necessary to find that balance. If there are patient set-up errors, there is a risk of the dose covering more of these organs and healthy tissue than it should, which can lead to serious consequences. However, it is impossible to always set up the patient in the same exact position, set-up errors will always occur, no matter how small. Given their dimension, these are hard to evaluate in terms of severity. This way, this dissertation studied the influence of patient set-up errors in specific organs of risk, the rectum and spinal cord. For this purpose, deviations in different directions were simulated, in several patient cases for both pathologies, by moving the irradiation isocenter, with the objective of analyzing their impact in dose calculation and distribution. With this, it was possible to conclude that rectal safety is compromised when it comes to set-up errors of at least -0,7 cm in the z axis, making it relevant to correct patient positioning from this point on, resulting in a risk of damage to the organ of a minimum level of 2 of up to 19 % and a minimum level of 3 of up to 3 %. Regarding the spinal cord, it was determined that patients should be repositioned given set-up erros of around -0,8 cm in the z axis, their risk of myelopathy being 6 %. Set-up errors that reach -1,0 cm in z reach a risk of 50 %.
Radiotherapy oncology treatment is an extremely important practice, but at the same time it demands a lot of carefulness, demanding a high degree of precision. A patient will be exposed to ionizing radiation with the purpose of eliminating tumors, but their safety must be garanteed and, for that, amongst other factors, it is necessary to ensure that their physical position in relation to the reference point is according to what is expected. Should this not be the case, the dose distribution of the treatment could be compromised. The intention is to maximize tumor coverage while patient irradiation is occurring, but said tumor will be in the proximity of organs of risk that must be protected, and it is necessary to find that balance. If there are patient set-up errors, there is a risk of the dose covering more of these organs and healthy tissue than it should, which can lead to serious consequences. However, it is impossible to always set up the patient in the same exact position, set-up errors will always occur, no matter how small. Given their dimension, these are hard to evaluate in terms of severity. This way, this dissertation studied the influence of patient set-up errors in specific organs of risk, the rectum and spinal cord. For this purpose, deviations in different directions were simulated, in several patient cases for both pathologies, by moving the irradiation isocenter, with the objective of analyzing their impact in dose calculation and distribution. With this, it was possible to conclude that rectal safety is compromised when it comes to set-up errors of at least -0,7 cm in the z axis, making it relevant to correct patient positioning from this point on, resulting in a risk of damage to the organ of a minimum level of 2 of up to 19 % and a minimum level of 3 of up to 3 %. Regarding the spinal cord, it was determined that patients should be repositioned given set-up erros of around -0,8 cm in the z axis, their risk of myelopathy being 6 %. Set-up errors that reach -1,0 cm in z reach a risk of 50 %.
Descrição
Palavras-chave
Radioterapia Desvios Reto Medula Dose