Estimation of the Gamma Exposer Rate Constant for Clinically Relevant Radionuclides in Nuclear Medicine Using GATE/GEANT4 Monte Carlo Simulation
Abstract
Purpose. To establish a reliable computational method for calculating external radiation dose rates from nuclear medicine patients using Monte Carlo simulation and to systematically evaluate the effects of phantom geometry and detector characteristics on occupational exposure. Methods: MC GATE simulations version 9.1 (Geant4 10.7) calculated external dose rate constants for most clinical radionuclides: 99mTc, 67Ga, 18F, 11C, 131I, and 123I. Two phantoms were used, one with dimensions of (25×15×20, 30×20×25, and 35×25×30 cm3), and the other with a fixed length of 170 cm and variable width (15×20, 20×25, and 25×30 cm3), specific to the 99mTc nuclide. Detector sizes (3×3×3 to 10×10×10 cm³) were evaluated at distances of 1, 2, and 3 m. Different detector media (air, argon, and neon) were assessed for photon sensitivity. The results were compared with experimental data. Results: Simulated results agreed with experimental data within ±10%. Argon demonstrated superior sensitivity compared with air and neon detector media. Phantom dimensions increased overall, resulting in a 36.8% reduction due to self-attenuation. Radionuclides of 18F and 11C, followed by 67Ga, 131I, 123I, and 99mTc, posed the highest occupational exposure hazard. Patient body thickness was a more significant attenuation factor than patient height. Conclusion: GATE/Geant4 simulations provide a reliable and accurate tool for evaluating external dose rates in nuclear medicine departments. These findings underscore the importance of using appropriate detector sizes and media, as well as realistic patient geometry, in occupational dose assessments and provide essential data to improve radiation protection protocols.
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Copyright (c) 2026 Abdulkhaleq O. Jaralah, Alaa M. Elgohary, Monira M. Rageh, Magdy M. Khalil
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