Evaluation of the radiation dose in the thyroid gland using different protective collars in panoramic imaging

Background: The value for the use of thyroid shield is one of the issues in radiation protection of patients in dental panoramic imaging. Objectives: The objective of this research is to investigate the attenuation characteristics of some models of thyroid shielding in dental panoramic examinations. Methods: The effects of five different types of lead and lead-free (Pb-equivalent) shields on dose reduction of thyroid gland were investigated using implanted Thermoluminescence Dosemeters (TLDs) in head-neck parts of a Rando phantom. Results: The results show that frontal lead and Pb-equivalent shields can reduce the thyroid dose around 50% and 19%, respectively. Conclusions: It can be concluded that the effective shielding area is an important parameter in thyroid gland dose reduction. Lead frontal collars with large effective shielding areas (>similar to 300 cm(2) but not necessarily very large) are appropriate for an optimized thyroid gland dose reduction particularly for the critical patients in dental panoramic imaging. Regardless of the shape and thickness, using the Pb-equivalent shields is not justifiable in dental panoramic imaging.