A manufacturer's role in reducing the dose of cone beam computed tomography examinations: effect of beam filtration

Abstract

The dosimetry of the Kodak 9500 cone beam CT (CBCT) unit (Carestream Health, Rochester, NY) was measured before and after installation of copper filtration. Dosimetry of a pre-production Kodak 9500 CBCT unit was compared with a current production unit with 0.4 mm of added filtration and increased kVp. Thermoluminescent dosimeter 100 chips were placed at 24 locations in a RANDO (radiation analogue dosimetry) head phantom (Nuclear Associates, Hicksville, NY). Small, medium and large adult default exposure settings were used in separate dosimeter runs for large and medium field of view (FOV) examinations with both units. Equivalent dose and effective dose were calculated using International Commission on Radiological Protection (ICRP) 1990 and 2007 tissue weights. Estimations of risk using 2007 ICRP calculations increased by an average of 77% for large FOV scans and 125% for the medium FOV scans in comparison with 1990 calculations. With added filtration, effective dose for medium FOV examinations for default settings were: small adult 76 µSv, medium adult 98 µSv, and large adult 166 µSv. Effective doses for large FOV examinations were: small adult 93 µSv, medium adult 163 µSv, and large adult 260 µSv. Effective dose was reduced by an average of 43% in examinations made with increased filtration and adjusted kVp. The manufacturer's installation of additional filtration with the adjustment of kVp in the Kodak 9500 CBCT unit resulted in significant patient dose reductions for examinations at all adult default settings.