Impact of thyroid gland shielding on radiation doses in dental cone beam computed tomography with small and medium fields of view

Objective. The purpose of this study was to evaluate the impact of thyroid gland shielding on radiation doses in dental cone beam computed tomography (CBCT) with small and medium fields of view (FOVs). Study Design. Six CBCT protocols were investigated by exposing an adult anthropomorphic male phantom head without and with thyroid shielding, using 4 small (4 x 5 cm) and 2 medium (10 x 6 cm) FOVs. Twenty metal oxide semiconductor field-effect transistor dosimeters were placed in the phantom head to measure absorbed doses and calculate equivalent doses at 11 sites. Effective doses were calculated based on the tissue weighting factors in International Commission on Radiological Protection Publication 103. The data were analyzed using the independent samples t test. Results. Thyroid gland shielding led to significant equivalent dose reductions in many tissues for all protocols. Equivalent dose reductions to the thyroid were significant in all 6 protocols (P <=.037). Significant reduction depended on the FOV and ranged between 24.5% and 42.6% for the thyroid gland and 4.9% and 34.5% for other tissues and organs. Effective doses were significantly lower in all protocols (P <=.016). Conclusions. Thyroid gland shielding protects the thyroid gland and other organs and should be utilized with all CBCT examinations where feasible.