Room: Exhibit Hall | Forum 9
Purpose: To determine the magnitudes of free in air (FIA) correction factors for application to dose length product (DLP) of scans acquired using cone beam CT (CBCT), and study their dependence on kV and beam width.
Methods: Correction factors based on FIA measurements for CBCT, applied to measurements for a reference beam of width â‰¤ 40 mm, have been proposed by the International Electrotechnical Commission to overcome limitations of the volume CT dose index (CTDIvol) in assessing patient doses. A validated Monte Carlo model of a kV on-board imaging (OBI) system was used to assess the correction factors for head and body scan protocols using tube potentials of 80 â€“ 140 kV. The factors were derived for cone beams with widths 80 â€“ 300 mm, and a reference beam width of 20 mm.
Results: The FIA correction factors were comparable for the scan protocols studied, where all factors were in the range 0.99 â€“ 1.02. The influence of tube potential on the factors was minimal, and the average variation with beam width over the range studied was 1.01.
Conclusion: DLP of CT scans plays a vital role in, for example, estimation of effective doses of patients undergoing scans, and in shielding calculations. The largest FIA correction factors required, only amounted to an adjustment of 2% in this study, are recommended for application to CBCT scans in order to avoid underestimation of doses delivered to patients from CBCT scans.
Not Applicable / None Entered.