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 time s raises the question as to whether there is a significant radiation d ose to the radiographer. We have measured the radiation dose to the op erator from studies performed on four DXA systems; the Lunar DPX, Holo gic QDR-1000, QDR-2000plus and QDR-4500. The results were compared wit h the radiographer dose from Tc-99(m)-MDP radionuclide bone scanning, where it is not usual to use a radiation barrier between the patient a nd the operator, and F-18-FDG positron emission tomography (PET) scann ing where it is usual to protect staff. Ambient dose equivalent rate a veraged 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. Ann ual operator dose for the DPX and QDR-1000 was well below the 1 mSv li mit for members of the public recommended by the International Commiss ion on Radiological Protection (ICRP) (1990). Results for the QDR-2000 plus 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 cl ose to the 5 mSv year(-1) limit for a supervised area defined in the 1 985 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 sca n modes with short scanning times.