Thyroid shields and neck exposures in cephalometric radiography

Abstract

Background: The thyroid is among the more radiosensitive organs in the body. The goal of this study was twofold: (1) to evaluate age-related changes in what is exposed to ionizing radiation in the neck area, and (2) to assess thyroid shield presence in cephalometric radiographs Methods: Cephalometric radiographs at one academic setting were sampled and neck exposure was related to calendar year and patient's gender and age. Results: In the absence of shields, children have more vertebrae exposed than adults (p less than 0.0001) and females have more neck tissue exposed inferior to the hyoid bone than males (p less than 0.0001). The hyoid bone-porion distance increased with age (p less than 0.01). Thyroid shields were visible in 19% of the radiographs and depended strongly on the calendar year during which patient was seen (pvalue less than 0.0001). Compared to adults, children were less likely to wear thyroid shields, particularly between 1973 and 1990 (1.8% versus 7.3% - p-value less than 0.05) and between 2001 and 2003 (7.1% versus 42.9% - p-value less than 0.05). Conclusion: In the absence of a thyroid shield, children have more neck structure exposed to radiation than adults. In agreement with other reports, thyroid shield utilization in this study was low, particularly in children.