Assessment of radiation dose in dual energy X-ray absorptiometry scanner

Objective To evaluate the radiation dose from a dual energy X-ray absorptiometry (DXA) study. Methods A Radcal multifunctional dosimeter (1 800 cc ionization chamber, USA) was used, for purpose of comparison, to measure the entrance surface doses (ESD) from Norland XR-800 DXA (pencil beam scan, 100/46.8 kVp, 1.3 mA) and from Hologic Discovery A DXA (fan beam scan, 140/100 kVp, 5.0 mA). Ambient dose equivalent rate at 1 m away from studied phantom center and at 1 m above floor was measured using the US 451P ionizaion chamber survey meter (Fluke, USA). Results The ESD measured using a Radcal dosimeter for Norland XR-800 DXA was 0.43 μGy in high speed mode and 0.73 μGy in standard mode (AP spine), 1.93 μGy (hip), 0.40 μGy (wrist) and 1.06 μGy (mandible). The ESD measured for Hologic Discovery A DXA was 65.6 μGy (AP spine) and 63.9 μGy (hip). The ESD measured for Norland XR-800 at different scan types and scan speeds was <2 μGy while Hologic Discovery A DXA showed a result of <66 μGy (AP spine and hip scan), which were both consistent with the data given in their own respective operational manual. A comparison of DXA scanners with fan beam and pencil beam indicated that ambient equivalent dose rate, measured with 451P survey meter, from fan beam scan was 65 times that from pencil beam scan. Conclusions Compared with other medical X-ray studies, the ESD to the phantom undergoing a DXA study is relatively low. DXA pencil beam scan doses to lumbar spine and hip were about 1/153-1/33 of those from DXA fan beam scan. Pencil beam scan dose to DXA staff was negligible and fan beam scan dose to DXA staff was lower than the personal dose limits of 20 mSv per year. Key words: Dual energy X-ray absorptiometry(DXA) scanner; Radiation protection; Entrance surface dose(ESD)