Avaliação do efeito de próteses de silicone em um tratamento de radioterapia de mama utilizando simulação Monte Carlo

Abstract

Breast cancer became the most incident in the world in 2020, with Brazil being the South American country with the highest number of breast cancer cases among women. Radiotherapy is a form of treatment for this type of cancer and may be applied before and after mastectomy and breast reconstruction, in which a silicone prothesis is implanted to replace the removed breast tissue. The Monte Carlo simulation tool (MCNP 6.2), used together with a female anthropomorphic phantom (FASH3), was used to quantify the absorbed doses in the patient's organs and tissues. The survey of absorbed doses was carried out to evaluate the effect of the breast silicone implant on dose distribution, when submitted to radiotherapy treatment with the 6 MV beam and applying a dose of 50.4 Gy. The beam validation was performed by comparing experimental data and those simulated computationally through percentage depth dose and off-axis dose profiles parameters. The results showed a good correlation between the experimental and simulated values, with percentage differences of 5% for the percentage depth dose curves and 3% for the central region (-5 to 5 cm) of the off-axis dose profile curves, showing that the MCNP 6.2 tool is suitable and effective for calculating the absorbed dose of the organs and tissues of the FASH3 phantom. The gallbladder and bone surface were the organs that suffered the highest contribution of scattered radiation by the silicone prosthesis, increasing the absorbed dose values by 1.36% and 1.29%, respectively, when compared to normal breast tissue. The reason for the highest dose values in these organs is due to the fact that they are positioned close to the target beam incidence during treatment. The results of the absorbed dose values obtained showed that the dose distribution did not undergo a significant change in the presence of the silicone implant, only a low increase in the absorbed dose in organs close to the area of breast irradiation were observed for the configuration studied in this work.