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.
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)