Comprehensive assessment of broad beam transmission factors for nuclear medicine shielding

This study aims to calculate broad beam transmission factors (BBTF) for common nuclear medicine shielding materials (lead, lead glass, concrete, barite concrete, and iron) using consistent Monte Carlo (MC) simulations. Additionally, the feasibility of fitting these transmission factors to the Archer model was explored.

Photon emission spectra and biodistributions of eleven radionuclides (¹¹C, ¹⁵O, ¹⁸F, ⁶⁷Ga, ⁶⁸Ga, ^99mTc, ¹²³I, ¹³¹I, ¹⁵³Sm, ¹⁷⁷Lu, and ²⁰¹Tl) were analyzed. BBTFs were calculated for five shielding materials using both point sources and anthropomorphic phantoms to reflect practical clinical conditions. Validation was performed by comparing results with published data.

BBTFs for eleven radionuclides and five shielding materials were obtained. The calculated half-value layer, tenth-value layer, centesimal value layer, and millesimal value layer thicknesses demonstrate good agreement with experimental and reference data for point sources. Results for phantom sources extend existing methodologies for PET shielding calculations to other radionuclides used in clinical practice. Findings indicate a reduction in shielding thickness due to changes in the radiation spectrum from body self-attenuation and highlight the impact of radionuclide biodistribution on BBTFs. The Archer model was not suitable for all sources, particularly low-energy ones.

The study provides a validated basis for BBTF calculations across different sources and materials. Results demonstrate the need to account for body self-attenuation and biodistribution in shielding design. Future work should consider different biodistributions, phantom positions and generalized fitting models.