Estimating Thyroid Doses from Modified Barium Swallow Studies

This study sought to obtain factors to convert entrance air kerma into thyroid doses for patients undergoing modified barium swallow studies. A commercial software package (PCXMC 2.0.1) was used to calculate patient thyroid doses from modified barium swallow studies, which were divided by the entrance air kerma to yield f_thyroid ratios. Exposure in the lateral and posterior-Anterior projections were considered where the thyroid was directly irradiated. Calculations were obtained for adult patients as well as children ranging from birth to 10 y old. The average value of f_thyroid in a normal-sized adult was 0.63 ± 0.11 in the lateral projection and 0.18 ± 0.06 for an upper gastrointestinal posterior-Anterior projection. Increasing the beam quality from the lowest (60 kV + 3 mm aluminum) to the highest (110 kV + 3 mm aluminum + 0.2 mm copper) values investigated nearly doubled the value of f_thyroid from 0.42 to 0.79 in the lateral projection and quadrupled the value from 0.07 to 0.29 in the upper gastrointestinal posterior-Anterior projection. Values of f_thyroid decreased with increasing body mass index. Average values of f_thyroid in 10 y olds were similar to those of adults but always increased as the age of the exposed child was reduced. The average f_thyroid for newborns was 0.84, nearly one-Third higher than the corresponding ratio for normal-sized adults.