An assessment of the radiation dose to patients and staff from a Lunar Expert-XL fan beam densitometer.

Dual-energy x-ray absorptiometry (DXA) is a widely used technique for measuring bone mineral density for the identification and management of osteoporotic subjects. The original DXA pencil beam systems expose patients to an effective dose of ionizing radiation of around 2 muSv and require no additional protective shielding for staff. The new fan beam densitometers incorporate solid state detectors and have a higher photon flux, enabling faster acquisition times and giving improved resolution. However, this may be at the expense of higher radiation dose. This study was conducted to assess the radiation dose to patients and staff from the standard scan modes using a Lunar Expert-XL fan beam densitometer. This is, we believe, the first dose assessment of the Expert-XL. The results indicate that the scatter dose at 1 m from the scan table, assuming four AP spine and femoral neck examinations per hour, is about 4 muSv h-1. This is well below the limit of 7.5 muSv h-1 set by the UK's Ionising Radiation Regulations for defining a Controlled Area but above the lesser limit of 2.5 muSv h-1 for a Supervised Area. Typical effective doses to patients are 59 muSv for an AP lumbar spine scan, up to 56 muSv for AP femoral neck, 71 muSv for lateral spine morphometry and 75 muSv for whole body. Although exceeding those of pencil beam DXA machines, these doses are less than for standard radiographic procedures, particularly of the lumbar spine. Where reduced scan time, improved image resolution or morphometric analysis of the spine are required, the patient doses from the Lunar Expert-XL are not prohibitive.