Investigation of thyroid dose due to mammography.

The radiation dose to the skin overlying the thyroid was measured for 91 women undergoing routine mammographic screening. Measurement was made over 6 days using thermoluminescent dosimeter (TLD) detectors taped appropriately to the neck. An average skin dose of 0.39 +/- 0.22 mGy per mammographic examination was measured with measurements ranging from background levels to 1.15 mGy. The average dose was significantly correlated to the milliampere-seconds for a total procedure. The mediolateral-oblique view was found to give a 2.4-fold greater skin dose at the thyroid than the craniocaudal view. After considering depth dose data from the literature it was conservatively estimated that the dose to the thyroid gland might be 10% of the skin dose overlying the thyroid. This corresponds to an average thyroid dose during mammography of approximately 0.04 mGy which is considered insignificant compared with the average breast dose (4 mGy) and in light of the relevant available literature on the risk to the thyroid.