External dose characteristics and radiation-protection metrics after permanent 125I prostate brachytherapy: comparison of conventional and sparse implantation techniques.

This study compared external dose rates and radiation protection metrics between the conventional whole-gland technique (CWT) and sparse implantation technique (SIT) in 100 patients (50 each with CWT and SIT) undergoing permanent 125I prostate brachytherapy. External dose rates were measured at various distances from the anterior body surface at 1 and 30 days post-procedure. Time-dependent dose rates were estimated using an exponential decay model based on the physical half-life and compared with measured values. Lifetime cumulative effective dose, cumulative effective dose during the first 60 days, and distance-specific precaution periods were also evaluated using occupancy factors. SIT reduced external radiation exposure and shortened the precaution period compared with CWT. The precaution period increased nonlinearly at closer ranges and was consistently shorter in the SIT group compared with the CWT group. Utilizing cumulative effective dose assessments during the initial 60 days post-procedure provides a practical radiation protection indicator for real-world environments.