Assessment of thyroid dose in orthopantomogram imaging with different thyroid shield materials: a Monte Carlo simulation study.

Radiation protection in dental radiography can be achieved by adjusting the image field size, exposure, and filtration parameters, and using protective lead shields. The aim of this study is to assess the radiation dose delivered to the thyroid in a phantom irradiated by an orthopantomogram (OPG) system using Geant4 simulation toolkit. Recently, researchers have been trying to find an alternative material to the lead thyroid shield so that the OPG image has minimal metal artifacts. In this study, several materials were introduced as alternatives to lead thyroid shields. The results showed that Pb, Bi, Bi2O3, stainless steel, polyurethane-Bi2O3 (50%-50% mixture), and polyurethane-W (50%-50% mixture) shields provide a thyroid dose reduction of up to 12.0%, 12.3%, 12.0%, 11.6%, 11.8%, and 12.0%, respectively. For the truncated thyroid shields, these values are up to 10.5%, 10.3%, 10.3%, 9.80%, 10.0%, and 10.1%, respectively. Therefore, Bi and Bi2O3 can be suitable alternatives to lead thyroid shields.