Personnel exposure rates during simulated biopsies with a real-time CT scanner

Real-time computed tomography (CT) has the potential to expedite and improve CT-guided needle biopsies by allowing cross-sectional images to be viewed in real time as a needle is advanced toward the target lesion. A major concern about this procedure is the scattered and leaked radiation to which the operator is exposed. This study was undertaken to determine the exposure rates around a CT scanner during CT-guided needle biopsies and to identify the areas of greatest personnel exposure.

Pig and human cadavers were used to simulate patients undergoing a CT-guided needle biopsy. Various anatomic biopsy sites were used. The radiologist's exposure was assessed by timing the procedure and measuring the exposure rates around the CT scanner with an ionization-chamber survey meter. Ion-chamber measurements multiplied by the time the radiologist spent performing several mock biopsies were compared with film dosimeter results. Doses to the hands, wrists, and whole body were measured with ring, wrist, body, and collar film dosimeters.

The average time required to perform a single biopsy was about 1 minute. The dose to the radiologist performing the simulated biopsies was calculated to be 123 mR, 68 mR, 14 mR, and less than 0.5 mR to the fingers, wrist, collar, and body, respectively, as calculated from ionization-chamber and time measurements. These exposure rates correlate well with the film dosimeter readings accumulated during the mock procedures.

The dose received by the radiologist performing a CT-guided biopsy was comparable to that of other interventional procedures. In addition, operating from the head of the machine (ie, distal to the bed) appeared to markedly reduce personnel exposure, due to the shielding in the gantry of the CT scanner used in the study.