Bi2o3/Silicone Rubber Composite Thyroid Shield in Periapical Radiography: Experimental and Monte Carlo Assessment Publisher



Malekie S ; Shahbazi L ; Sardari D ; Kashian S ; Saadi M K
Source: Radiation Physics and Engineering Published:2026

Abstract

A thyroid shield composed of 70 wt% micro-sized Bi2O3 dispersed in a silicone rubber matrix was evaluated for radiation protection efficacy in periapical dental radiography. Absorbed dose to the thyroid gland was quantified using both Monte Carlo N-Particle (MCNP) simulations with a modified MIRD phantom and experimental measurements employing TLD-GR200 dosimeters positioned in the superior and inferior thyroid regions of a Rando anthropomorphic phantom. Irradiations were performed at 60 kV, 7 mA, and 0.32 s exposure time with a fixed 60◦ vertical angulation. Experimental results revealed thyroid absorbed doses of 72.7±25.7 µGy (unshielded), 40.9±15.6 µGy (commercial collar equivalent to 0.5 mm Pb), and 20.8±12.5 µGy (composite shield), corresponding to a 71.4% dose reduction with the composite shield, (compared to 43.7% for the commercial collar). Monte Carlo simulations at 60◦ angulation demonstrated dose reductions of 85.1% (commercial), and 83.3% (composite). Additionally, under SSDL inverse broad-beam conditions based on the IEC 61331-1 (RQR5, 70 kV), the composite shield achieved a 99.97% air kerma rate reduction, markedly superior to the 99.08% (commercial) and 98.13% (0.5 mm pure Pb). Although the composite shield exhibited superior shielding performance, its weight remains higher than commercial alternatives, indicating the need for further optimization. © 2026 by the journal.