Verificação do comportamento do parâmetro de cálculo TPR (DW) do TPS XiO® em função da energia do feixe, da profundidade de tratamento e das dimensões dos campos de radiação
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Data
2018-11-13
Autores
Navarro, Raphaella
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
A radioterapia é uma modalidade terapêutica que consiste no uso de radiação ionizante
para o tratamento de patologias, dentre elas o câncer. Os tratamentos podem ser realizados com
feixes de radiação dos tipos eletromagnética (raios-X ou raios gama) ou corpuscular (feixes de
elétrons ou prótons). Nos equipamentos do tipo aceleradores lineares clínicos são usados feixes
de raios-X ou de elétrons de alta energia. Nas unidades de telecobaltoterapia são aplicados
feixes de raios gama provenientes de fonte radioativa de cobalto-60. A dose de radiação liberada
pelos campos de radiação nos aceleradores lineares é representada em termos de unidade
monitora (UM). O cálculo das unidades monitoras envolve o conhecimento de vários
parâmetros radiométricos e geométricos dos feixes de radiação e das condições anatômicas das
áreas a serem tratadas. Os cálculos de UM são realizados pelos Sistemas de Planejamento de
Tratamento (TPS) computadorizados e devem ser conferidos pelos físicos da radioterapia que
realizam o cálculo manual. Esta prática de verificação dos cálculos é conhecida com double
check, que além de ser uma exigência das agências regulamentadoras dos serviços de
radioterapia, faz parte também do controle de qualidade do tratamento. O avanço tecnológico
dos aceleradores lineares possibilitou um aumento no range de energia, com isso houve a
necessidade de maior preocupação com a entrega de dose. Diante dessa necessidade e com
avanço da engenharia de computação os TPS´s computadorizados incrementaram algoritmos
mais precisos para determinação da distribuição da dose de radiação no campo de tratamento.
As recentes recomendações da Comissão Internacional de Unidades e Medidas (ICRU)
apontam que as diferenças entre os valores de UM determinados pelo TPS e calculados
manualmente pelo físico do serviço não deve ultrapassar ± 3,0 %. Neste trabalho foi estudado
os algoritmos de cálculos de UM de dois TPS´s, o TPS XiO da Elekta Medical Systems e o TPS
Eclipse da Varian Medical Systems. Com os dados radiométricos de campos de radiação,
aplicados nos serviços de radioterapia, foram analisados os comportamentos dos parâmetros
TPR, TMR e PDP em função da energia dos feixes, das dimensões dos campos de radiação e
profundidades de tratamento. Para os casos clínicos estudados, foi também analisado o erro
percentual dos valores de UM determinados pelos TPS e os calculados manualmente usando
planilhas Excel disponíveis nos serviços. Os resultados mostram que algumas geometrias de
campos podem implicar em erros acima dos recomendados pela literatura, realçando a
necessidade da realização rotineira do double check dos valores de unidade monitoras
Radiotherapy is a therapeutic modality that consists of the use of ionizing radiation for the treatment of pathologies, among them cancer. Treatments can be performed with beams of radiation of electromagnetic types (X-rays or gamma rays) or corpuscular (beams of electrons or protons). X-ray beams or high-energy electrons are used in clinical linear accelerator type devices. In the telecobaltotherapy units, bundles of gamma rays from the radioactive source of cobalt-60 are applied. The radiation dose delivered by the radiation fields on the linear accelerators is represented in terms of the monitoring unit (UM). The calculation of the monitor units involves the knowledge of several radiometric and geometric parameters of the radiation beams and the anatomical conditions of the areas to be treated. UM calculations are performed by Computerized Treatment Planning Systems (TPS) and should be checked by radiotherapy physicists performing the manual calculation. This practice of verification of the calculations is known with double check, which besides being a requirement of the regulatory agencies of radiotherapy services, is also part of the quality control of the treatment. The technological advance of the linear accelerators allowed an increase in the energy range, with which there was a need for greater concern with the delivery of the dose. Faced with this need and with advancement in computer engineering, computerized TPS has increased more accurate algorithms for determining the radiation dose distribution in the treatment field. The recent recommendations of the International Commission on Units and Measures (ICRU) point out that the differences between UM values determined by TPS and manually calculated by the service physicist should not exceed ± 3.0%. In this work we have studied the UM calculation algorithms of two TPS's, the TPS XiO from Elekta Meducal Systems and the TPS Eclipse from Varian Medical Systems. Radiometric data from radiation fields, applied in radiotherapy services, were analyzed for the behavior of the TPR, TMR and PDP parameters as a function of beams energy, radiation field dimensions and treatment depths. For the clinical cases studied, we also analyzed the percentage error of the UM values determined by TPS and those calculated manually using Excel spreadsheets available in the services. The results show that some field geometries may imply errors above those recommended by the literature, emphasizing the necessity of routine double check execution of monitor unit values
Radiotherapy is a therapeutic modality that consists of the use of ionizing radiation for the treatment of pathologies, among them cancer. Treatments can be performed with beams of radiation of electromagnetic types (X-rays or gamma rays) or corpuscular (beams of electrons or protons). X-ray beams or high-energy electrons are used in clinical linear accelerator type devices. In the telecobaltotherapy units, bundles of gamma rays from the radioactive source of cobalt-60 are applied. The radiation dose delivered by the radiation fields on the linear accelerators is represented in terms of the monitoring unit (UM). The calculation of the monitor units involves the knowledge of several radiometric and geometric parameters of the radiation beams and the anatomical conditions of the areas to be treated. UM calculations are performed by Computerized Treatment Planning Systems (TPS) and should be checked by radiotherapy physicists performing the manual calculation. This practice of verification of the calculations is known with double check, which besides being a requirement of the regulatory agencies of radiotherapy services, is also part of the quality control of the treatment. The technological advance of the linear accelerators allowed an increase in the energy range, with which there was a need for greater concern with the delivery of the dose. Faced with this need and with advancement in computer engineering, computerized TPS has increased more accurate algorithms for determining the radiation dose distribution in the treatment field. The recent recommendations of the International Commission on Units and Measures (ICRU) point out that the differences between UM values determined by TPS and manually calculated by the service physicist should not exceed ± 3.0%. In this work we have studied the UM calculation algorithms of two TPS's, the TPS XiO from Elekta Meducal Systems and the TPS Eclipse from Varian Medical Systems. Radiometric data from radiation fields, applied in radiotherapy services, were analyzed for the behavior of the TPR, TMR and PDP parameters as a function of beams energy, radiation field dimensions and treatment depths. For the clinical cases studied, we also analyzed the percentage error of the UM values determined by TPS and those calculated manually using Excel spreadsheets available in the services. The results show that some field geometries may imply errors above those recommended by the literature, emphasizing the necessity of routine double check execution of monitor unit values
Descrição
Palavras-chave
Dose de radiação, Sistema de Planejamento, Radioterapia, Unidade Monitora, Radiation dose, Planning System, Radiotherapy, Monitoring Unit