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 fthyroid 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 fthyroid 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 fthyroid 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 fthyroid decreased with increasing body mass index. Average values of fthyroid in 10 y olds were similar to those of adults but always increased as the age of the exposed child was reduced. The average fthyroid for newborns was 0.84, nearly one-third higher than the corresponding ratio for normal-sized adults.
1Health Sciences and Research, Medical University of South Carolina, 77 President Street, MSC 700, Charleston, SC 29425-2503;
2Department of Otolaryngology—Head and Neck Surgery, Medical University of South Carolina, 135 Rutledge Avenue, MSC 550, Charleston, SC 29425;
3Department of Radiology and Radiological Science, Medical University of South Carolina, 96 Jonathan Lucas Street, MSC 323, Charleston, SC 29425-3230;
4Communication Sciences and Disorders, Northwestern University, 70 Arts Circle Drive, Evanston, IL 60208;
5Department of Radiology, Dartmouth-Hitchcock Medical Center, 1 Medical Center Drive, Lebanon, NH 03766.
The authors declare no conflicts of interest.
For correspondence contact: Heather Shaw Bonilha, 77 President Street, MSC 700, Charleston, SC 29425, or email at firstname.lastname@example.org.
(Manuscript accepted 9 March 2018)