[OA134] Secondary analysis of canada’s national computed tomography (CT) survey data: digging deeper on DRLS

Purpose Following publication of Canada’s first national survey of Computed Tomography (CT) in 2016 [1] , Diagnostic Reference Levels (DRLs) are now available for select head and trunk examinations of both pediatric (0–3, 3–7 and 7–13 yrs.) and adult ( ≥ 19 yrs.) patients. The analysis performed also included additional investigation into the effect of scanning mode (axial or helical), contrast use (C+ or C−) and inclusion of dose reduction methods (Fixed or Dose Reduction (DR)). The intent was to investigate, at least semi-quantitatively whether this can help identify key protocols that could benefit from further optimization. Methods The Canadian CT survey was adapted from the 2003 CT survey performed in the United Kingdom [2] . In close collaboration with all Canadian provinces and territories, data was collected from approximately 75% of all CT scanners in Canada and ultimately provided machine, dose index, age, mass and cross-sectional dimension information from 24 280 individual patient sequences. For each patient sequence, an algorithm also scored and confirmed the scan mode, use of contrast and use of DR. CTDIvol data for each examination type (group) could then be sub-divided and compared with 8 sub-group DRLs or CTDIvol percentiles. E.g. Adult Head DRL versus Adult Head, Helical, C+ and Fixed current DRL, and so on. A custom graphic plot was created in order to clearly compare group (or examination) with sub-group dose index distributions. Results In almost all cases, the use of a fixed (non-modulated) current (mAs) showed higher CTDIvol values, across sub-group DRLs (75th percentile of CTDIvol sub-group data). Indicating that those protocols may potentially benefit most from dose reduction activities. Conclusions DRLs are an important part of dose reduction initiatives, and with some additional analysis, clear indicators can be produced that provide guidance on where to initiate any protocol review for potential dose reduction.