Occupational dose to the radiographer in dual X-ray absorptiometry: A comparison of pencil-beam and fan-beam systems

The introduction of advanced dual X-ray absorptiometry (DXA) scanners with fan-beam geometry, improved image definition and faster scan times raises the question as to whether there is a significant radiation dose to the radiographer. We have measured the radiation dose to the operator from studies performed on four DXA systems; the Lunar DPX, Hologic QDR-1000, QDR-2000plus and QDR-4500. The results were compared with the radiographer dose from Tc-99(m)-MDP radionuclide bone scanning, where it is not usual to use a radiation barrier between the patient and the operator, and F-18-FDG positron emission tomography (PET) scanning where it is usual to protect staff. Ambient dose equivalent rate averaged over 1 h at 1 m from the patient with the DXA systems working at maximum patient throughput were 0.012, 0.12, 2.1 and 2.4 mu Sv h(-1), respectively, for the DPX, QDR-1000, QDR-2000plus and QDR-4500. Annual operator dose for the DPX and QDR-1000 was well below the 1 mSv limit for members of the public recommended by the International Commission on Radiological Protection (ICRP) (1990). Results for the QDR-2000plus and QDR-4500 were similar to a radionuclide bone scan (2.2 mu Sv h(-1)), but smaller than for a PET scan (8.9 mu Sv h(-1)), and were close to the 5 mSv year(-1) limit for a supervised area defined in the 1985 Ionising Radiation Regulations. Precautions to reduce radiographer dose with fan beam DXA include placing the operator at least 2 m from the patient, scanning the right hip instead of the left and using scan modes with short scanning times.