Determinação experimental de parâmetros dosimétricos em diferentes feixes de fótons utilizados em radioterapia pela técnica Fricke

• Autor(a) principal: Rosado, Paulo Henrique Gonçalves
• Data de Publicação: 2018
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UERJ
• Texto Completo: http://www.bdtd.uerj.br/handle/1/16117
• topic: Dose absorbed; Fricke; Dosimetry; Metrology; X-Ray; Dosimetria; Metrologia; Raios X; Dose absorvida; Física Médica; Radiação Dosimetria; Fótons; Calibração; Radioterapia; CNPQ::CIENCIAS BIOLOGICAS::BIOFISICA

TRS#398 recommends that the dose absorbed to water for medium energy photon beams be determined to the water equivalent depth of 2 cm. For high energy beams the simulated Kq values are presented in TRS#398 and the experimental values are still under study. This thesis presents the Fricke dosimetry as a solution for the measurement of the dose absorbed to water in an absolute dosimetry for medium and high energy beams, in addition to the measurement of Kq values in an experimental way, since it is difficult to perform these measurements in other absolute standards. First, the chemical yield curve of the Fricke solution was determined as a function of the energy of the photons, considering the energies corresponding to medium energy X-ray photons, source of 137Cs and 60Co. From the chemical yield curve, it was possible to determine the absorbed dose in the water to the depth of 2 cm, equivalent in water, to medium energy X-ray beams defined by the CCRI / BIPM, as well as the expanded dose value uncertainties. For the CCRI / BIPM qualities, the spectra were also simulated and the parameter R5.2 was evaluated experimentally, to serve as a quality index for medium energy photon beams. The experimental values of the parameter R5,2 agree with an accuracy of 0.5% with the values of the literature. The expanded uncertainties of the obtained values were presented, as well as the values of the absorbed dose to water using the Fricke technique and an ionization chamber for dosimetry protocols, being the values considered compatible when the Zeta Index of the comparison was evaluated. The values found by the Fricke technique are equivalent to the values measured with an ionization chamber and have a difference smaller than 0.9%. The experimentally determined KQ values are in agreement with the simulated values with a difference of less than 0.3%.