Evaluation of the DXA radiation environment at Sahlgrenska University Hospital

Abstract

Purpose: The aims of this work were to evaluate the radiation environment in the dual-energy X-ray absorptiometry (DXA) rooms at Sahlgrenska University Hospital, estimate personnel doses, determine legal requirements for DXA personnel, examine the operators’ view on radiation safety and develop material with dose information for patients and operators. Theory: DXA is a low dose X-ray modality mainly used in osteoporosis examinations, for which it is considered the reference technique. Bone mineral density (BMD) is measured in the hip and the lumbar spine, and a typical protocol also includes a vertebral fracture assessment (VFA). The DXA operator is stationed in the same room without any shielding or protection during the scanning. With no regular dose measurements or calculations, most DXA operators do not know the amount of radiation they are exposed to, more than that the doses are low compared to other modalities. Personnel working with ionising radiation is generally classified as category A or B, depending on the amount of radiation they are at risk of being exposed to. Regarding DXA operators at Sahlgrenska University Hospital, there is a discussion on which category they should belong to. Currently, they are in category B, but another possibility is that they can be unclassified. Method: Measurements were performed at the DXA scanners Hologic Discovery A and GE Lunar iDXA with help from an experienced DXA operator. A whole-body phantom was used, and scattered radiation was measured at different positions in the room with the instrument RaySafe 452 Radiation Survey Meter. The standard osteoporosis protocol, consisting of the examinations Hip, AP Spine and VFA, was run, while air kerma (µGy) and air kerma rate (µGy/h) was measured. Two different phantom sizes were used in the Hologic scanner. The scattered radiation during each examination was displayed asisodose lines between points with the same air kerma rate, calculated with the inverse square law. Yearly effective doses (mSv) to the operators were calculated using PCXMC 2.0 at different distances and directions in the rooms. Minimum distances in the different directions were also calculated, where the operator can be positioned and with certainty not exceeding 1 mSv in yearly effective dose. Finally, a questionnaire was given to the four DXA operators at the osteoporosis centre, with questions regarding their views on radiation safety. Result: Effective doses at 2–3 meters from the centre of the scanner were under 1 mSv per year for both Hologic and GE operators in the two examined directions. Two meters from the GE scanner, perpendicular to the scanning direction, the yearly dose was 0.66 mSv, which was the highest value. However, in a position right next to the table, the doses were 2.8–7.3 mSv, showing that the levels of ionising radiation in a DXA room cannot be neglected. Different phantom sizes showed no clear effect on scattered radiation. The personnel survey showed that the operators feel safe, or somewhat safe, regarding the radiation in their workplace.