Assessment of external radiation exposure dose rates and protective strategies following I-125 permanent prostate implantation treatment

Iodine-125 (¹²⁵I) permanent prostate implantation, also known as brachytherapy, is a widely used treatment for localized prostate cancer. This procedure involves implanting radioactive ¹²⁵I seeds directly into the prostate gland, delivering targeted radiation to the tumor. A critical aspect of this therapy is assessing external radiation exposure to ensure safety for patients, healthcare workers, and the public. This study evaluated external radiation exposure from permanent prostate implantation therapy using direct measurements and Monte Carlo N-Particle (MCNP5) code simulations, specifically assessing the accuracy of simulated predictions against measured external radiation dose rates. The study included 21 patients with stage T1–T2a prostate cancer, treated between May 2013 and February 2016, who received ¹²⁵I implants through the perineum. External dose rates were measured in five directions at three distances from the patients' bodies. MCNP5 simulations based on post-treatment computed tomography (CT) images were compared with the measured dose rates. The results demonstrated a strong correlation (Spearman rank correlation coefficient >0.7892) between measured external radiation and the patients' water equivalent thickness (WET) derived from CT images. No statistically significant differences were observed between the measured and simulated dose rates at 30 cm (p > 0.05). The effective dose for the public and relatives remained within the limits set by the International Commission on Radiological Protection; however, caution is advised for children and pregnant women. In conclusion, this study established a reliable method for analyzing radiation dose rates using MCNP5 simulations to evaluate radiation safety following ¹²⁵I implantation. The precautionary times derived from Monte Carlo simulations can guide patient-specific radiation protection measures for close contacts. This approach provides valuable strategies to ensure radiation safety for medical staff, patients, and their families.