Comparison of effective dose to children and adults from dual X-ray absorptiometry examinations

Dual X-ray absorptiometry (DXA) is increasingly used to measure bone density in children. If the system software does not include pediatric scan modes, then child examinations must be performed using adult scan modes that give a higher radiation dose to children than adults. This report describes a study to compare the effective dose to children and adults from DXA scans performed on the Hologic Discovery and QDR4500 models. Depth dose measurements were made using thermoluminescent dosimeters in a Rando phantom and were mapped onto the Cristy mathematical phantoms representing a 5-, 10- and 15-year-old child and an adult, and effective dose (ED) was calculated using the ICRP Publication-60 tissue weighting factors. The ED for spine (hip) examinations performed with the Express mode using the default adult scan lengths were 16.1 (9.8), 11.1 (6.7), 5.6 (3.9) and 4.4 (3.1) microSv for a 5-, 10- and 15-year-old child and adult respectively. However, if care is taken to adjust scan lengths appropriately, the child doses were reduced to 9.1 (7.4), 7.1 (5.9) and 5.0 (3.7) microSv. ED figures for the Fast and Array modes were larger by factors of 1.5 and 3 respectively. EDs for whole body scans for a 5-, 10- and 15-year-old child and adult performed on the A-model (W-model) were 5.2 (10.5), 4.8 (9.6), 4.2 (8.4) and 4.2 (8.4) microSv. Using the infant whole body mode (only available on the A-model), they were 7.5 microSv for a 1-year-old and 8.9 microSv for a neonate. Although doses from child DXA examinations are low, it is still important to keep them as small as possible. DXA operators using Discovery systems can do this by using the Express scan mode, by setting appropriate values of the scan length before scan acquisition and by avoiding mistakes that lead to scans having to be unnecessarily repeated.