Poster — Wed Eve—02: Monte Carlo Dose Calculation of Critical Organs in MDR Cs‐137 Afterloading Intracavitary Brachytherapy

The aim of this study is to perform Monte Carlo dose calculations on two critical organs, bladder and rectum, by considering the effects of applicator attenuation for three different applicator diameters of the Selectron/MDR intracavitary brachytherapy system. Three different pelvic phantoms, with a gynecological cylinder, were used to simulate the treatments. Dosimetric measurements were carried out in five different positions in the rectum and one position in the bladder using p‐type diode detectors. The absorbed doses at clinical points in the phantoms were calculated using the MCNP5 Monte Carlo code and the PLATO commercial treatment planning system (TPS). It was found that the dose‐rate constant for the pellet source was [formula omitted] with uncertainty within 1.33% compared to the latest published data. In all cases, results of the Monte Carlo based calculations agreed better with measured doses than those of the PLATO TPS, with the maximum deviation occurring for the 3 cm diameter applicator in the rectum. The largest discrepancy seen in this study, between measured dose and the TPS calculated dose, was 7.1%. The Monte Carlo calculation, for the same position, had a dose discrepancy of 3.0%. The average deviation between the PLATO TPS calculated doses and measured doses was approximately double what was seen between the Monte Carlo results and measured doses. This is due to the absence of the applicator attenuation effect in the PLATO TPS. Therefore, Monte Carlo simulation can be considered a more accurate dose calculation method in this study.