Optimizing dosimeter placement for radiation protection in nuclear medicine: A Monte Carlo simulation study

This study examined the optimal placement of personal dosimeters for radiation workers in nuclear medicine to improve the accuracy of organ dose estimation, particularly in the presence of lead apron shielding.

Monte Carlo simulations were carried out using the GATE toolkit with the Livermore low-energy physics model. ICRP reference male and female computational phantoms were used as radiation-worker models, and an additional ICRP male phantom represented the patient/source. F-18, I-131, and Tc-99m were simulated at source-to-worker distances of 0, 1, and 3 m with lead-equivalent apron thicknesses of 0, 0.125, 0.25, and 0.5 mm. The radionuclide source was represented by a uniform cylindrical tissue-equivalent volume. Simulations used 10^8 primary-particle histories per modeled condition; no patient-specific administered activity was assigned.

The outer and under-apron dosimeters showed different relationships with doses to uncovered and apron-covered organs, respectively. Linear fits for F-18 had R² > 0.90, whereas logarithmic fits for I-131 and Tc-99m had R² > 0.85. Increasing apron thickness changed under-apron readings in a radionuclide-, phantom-, and geometry-dependent manner, with the largest relative changes observed for Tc-99m. Source-to-worker distance generally reduced the modeled dose readings. These findings describe the behavior of the modeled exposure geometry but do not constitute clinical validation of a dual-dosimeter protocol.

The simulations indicate that dosimeter position can influence the interpretation of exposure in partially shielded nuclear medicine workers. The findings support further experimental and occupational-dosimetry evaluation of task- and geometry-specific monitoring configurations, rather than immediate modification of occupational monitoring protocols or radiation-protection guidelines.