Patient and staff dose during CT guided biopsy, drainage and coagulation

Patient and staff dose during CT guided coagulation of osteoid osteoma, tissue biopsy and abcess drainage were evaluated retrospectively on a conventional CT scanner and prospectively on a scanner equipped with fluoroscopic CT. The computed tomography dose index (CTDI) and the individual dose equivalent, i.e. the penetrating dose for workers at a depth of 10 mm tissue, were measured. Evaluation of CTDI enabled effective dose and maximum skin entrance doses for the patient to be determined. Doses were assessed for 96 CT guided interventions, including 16 drainages with average effective doses of 13.5 mSv and 9.3 mSv for the conventional CT scanner and the scanner with spiral CT fluoroscopy, respectively, 49 biopsies (effective doses of 8 mSv and 6.1 mSv, respectively), and 31 coagulations of osteoid osteoma (effective doses of 2.1 mSv and 0.8 mSv, respectively). Effective doses to patients were in the same range as those observed for regular diagnostic CT examinations. Entrance skin doses were well below the 2 Gy threshold for deterministic skin effects on the CT scanner equipped with fluoroscopic function (0.03-0.33 Gy), whilst skin doses on the conventional scanner were considerably higher (0.09-1.61 Gy). This is mainly owing to the fact that on the conventional scanner mAs was rarely reduced for scans evaluating needle position whereas low mAs per rotation was selected on the scanner with the fluoroscopy option. The maximum dose to a worker measured outside the lead apron was 28 mu Sv for one single procedure. The mean dose per procedure was below 10 mu Sv for radiologists and below 1 mu Sv for radiographers. Correcting for attenuation of the lead apron, the doses to workers are very low.