Uso do Método de Monte Carlo para determinação das doses de radiação em braquiterapia com sementes de 125I para o tratamento de câncer de próstata

Abstract

Prostate cancer is the second most common cancer among men in the world and the most common among them in Brazil. For its treatment, a widely used therapy technique is 125I radioactive seed brachytherapy. Due to the growing innovation in products for this therapy, the versatility of the Monte Carlo Method and the increasing number of people being diagnosed with prostate cancer, in this conclusion work, the radiation doses of 125I seeds developed at IPEN/CNEN-SP in a prostate cancer brachytherapy treatment were computationally evaluated. For this purpose, a virtual male anthropomorphic phantom was used, where it is possible to determine absorbed doses in certain organs and tissues and their effective dose. Three studies were conducted to evaluate the performance of the national 125I seed: energy fluency, anisotropy and determination of radiation doses in various organs and tissues, comparing their results with those of the commercial 125I seed Amersham 6711Oncoseed®, employed in routine prostate brachytherapy. In the first characterization, the obtained data showed that the seeds emit high energy fluency along their longitudinal axis and smaller in their extremities. In the second study, the two 125I seed models presented a similar dose emission between the angles of 20º to 170º, and the factor that influences the anisotropy function is only the polar angles below 20º and above 170º, a justifiable fact by the differences shields and end geometries of the two 125I seed models. The percentage differences between the two geometries were higher than 2%. In the determination of doses through a virtual phantom, the two seeds presented the same effective dose during the prostate cancer brachytherapy procedure, just as the absorbed doses in some organs and tissues were the same for both models. The prostate was the organ that received the highest dose, as it was the target organ of treatment, followed by the bladder, colon and gonads, compared to the other organs evaluated, because they are near the place of insertion of the radioactive seeds. Studies comparing IPEN 125I and commercial seeds (Amersham 6711-Oncoseed®) have showed the excellent performance of the national seed, obtaining similar results in the treatment of prostate cancer.