Residual Radioactivity Concentration Analysis and Storage Period Calculation for Tc-99m Contaminated Medical Wastes

Purpose: This study aimed to evaluate residual radioactivity concentrations in different types of medical radioactive waste contaminated with Tc-99m to determine optimal storage periods and develop efficient waste management strategies for nuclear medicine facilities. Materials and Methods: Radioactively contaminated waste generated from July 2022 to December 2024 was collected from radiation-controlled areas and categorized by waste type including glass vials, syringes, injection needles, and alcohol swabs. Radioactivity measurements were performed using a calibrated radioisotope dose calibrator, and mass measurements employed precision electronic balances. Adsorption rates and residual radioactivity concentrations were calculated for each waste category using standardized protocols. Storage periods were determined using radioactive decay formulas with a conservative safety factor of 1.2 applied to theoretical concentrations. Results: Significant variations in residual radioactivity were observed across waste types. Glass vials demonstrated the highest adsorption rate at 46% with residual activity of 1.7×1010Bq, while syringes and needles retained 3% and 1% respectively. Despite low adsorption percentages, injection needles exhibited the highest mass-normalized radioactivity concentration at 4.81×109 Bq/g due to minimal mass. Required storage periods ranged from 5.80 days for alcohol swabs to 6.68 days for glass vials, with needles requiring 6.50 days and syringes 6.15 days. All calculated periods remained within one week, making self-disposal feasible for short-lived radionuclides. Conclusion: This systematic evaluation provides quantitative, science-based guidelines for optimizing storage periods of Tc-99m contaminated medical waste. The methodology establishes a reference framework for developing self-disposal strategies for isotopes with half-lives under five days, contributing to more efficient and cost-effective radioactive waste management protocols in medical settings while ensuring regulatory compliance and public safety.