RADIATION-DOSE AND IN-VITRO PRECISION IN PEDIATRIC BONE-MINERAL DENSITY-MEASUREMENT USING DUAL X-RAY ABSORPTIOMETRY

Dual X-ray absorptiometry (DXA) is one of the most widely used techniq ues 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 estimat e the effective doses (EDs) received by typical 5- and 10-year-old chi ldren using the paediatric scan mode on the Lunar DPX-L bone mineral d ensity scanner. Entrance surface doses (ESDs) and percentage depth dos es for the total body and PA spine scan modes were measured using lith ium berate thermoluminescent dosemeters (TLDs) located at the surface and distributed at various organ locations in anthropomorphic child ph antoms. The EDs were calculated from the percentage depth doses, amoun t of each organ irradiated and tissue weighting factors. The ESDs were measured to be 6.0 and 0.12 mu Gy for the postero-anterior (PA) spine and total body, respectively. PA spine EDs were calculated as 0.28 an d 0.20 mu Sv for the 5- and 10-year-old, respectively. Total body EDs were 0.03 and 0.02 mu Sv for the 5- and 10-year-old children, respecti vely. These results compare with an adult ED of 0.21 mu Sv for the PA spine. They are also more than two orders of magnitude lower than repo rted ESDs and EDs for paediatric chest X-rays. Bone mineral density (B MD) short-term in vitro precision was 0.5% and 1% in the 5- and 10-yea r-old phantoms, respectively. In conclusion, the Lunar DPX-L in the pa ediatric mode has a high precision and very low radiation doses, simil ar to those reported for the adult mode.