Radiation dose and in vitro precision in paediatric bone mineral density measurement using dual X-ray absorptiometry

Dual X-ray absorptiometry (DXA) is one of the most widely used techniques for non-invasive assessment of bone integrity. There is a growing demand for measurement of paediatric bone status. In DXA the principal radiation risks to patients are the carcinogenic and genetic effects. Radiation dosimetry is well established for DXA in adults, but there are limited paediatric data available. We report on a study to estimate the effective doses (EDs) received by typical 5- and 10-year-old children using the paediatric scan mode on the Lunar DPX-L bone mineral density scanner. Entrance surface doses (ESDs) and percentage depth doses for the total body and PA spine scan modes were measured using lithium borate thermoluminescent dosemeters (TLDs) located at the surface and distributed at various organ locations in anthropomorphic child phantoms. The EDs were calculated from the percentage depth doses, amount of each organ irradiated and tissue weighting factors. The ESDs were measured to be 6.0 and 0.12 microGy for the posteroanterior (PA) spine and total body, respectively. PA spine EDs were calculated as 0.28 and 0.20 microSv for the 5- and 10-year-old, respectively. Total body EDs were 0.03 and 0.02 microSv for the 5- and 10-year-old children, respectively. These results compare with an adult ED of 0.21 microSv for the PA spine. They are also more than two orders of magnitude lower than reported ESDs and EDs for paediatric chest X-rays. Bone mineral density (BMD) short-term in vitro precision was 0.5% and 1% in the 5- and 10-year-old phantoms, respectively. In conclusion, the Lunar DPX-L in the paediatric mode has a high precision and very low radiation doses, similar to those reported for the adult mode.