Patient and staff dose during CT guided coagulation of osteoid osteoma, tis
sue biopsy and abcess drainage were evaluated retrospectively on a conventi
onal CT scanner and prospectively on a scanner equipped with fluoroscopic C
T. The computed tomography dose index (CTDI) and the individual dose equiva
lent, i.e. the penetrating dose for workers at a depth of 10 mm tissue, wer
e measured. Evaluation of CTDI enabled effective dose and maximum skin entr
ance doses for the patient to be determined. Doses were assessed for 96 CT
guided interventions, including 16 drainages with average effective doses o
f 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 (effect
ive doses of 2.1 mSv and 0.8 mSv, respectively). Effective doses to patient
s were in the same range as those observed for regular diagnostic CT examin
ations. Entrance skin doses were well below the 2 Gy threshold for determin
istic skin effects on the CT scanner equipped with fluoroscopic function (0
.03-0.33 Gy), whilst skin doses on the conventional scanner were considerab
ly higher (0.09-1.61 Gy). This is mainly owing to the fact that on the conv
entional scanner mAs was rarely reduced for scans evaluating needle positio
n whereas low mAs per rotation was selected on the scanner with the fluoros
copy option. The maximum dose to a worker measured outside the lead apron w
as 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.