National collection of local diagnostic reference levels in Norway and their role in optimization of X-ray examinations

The concept of diagnostic reference levels (DRLs) is recognised as an efficient and powerful tool in optimization of diagnostic X-ray examinations. Norway was one of the pioneer countries in establishing national DRLs, but focus on implementation and use of DRLs locally at the clinics in optimization purposes has been absent until now. The aim of this study was to map the dose levels and optimization potentials by carrying out a national collection of local DRLs. Totally 40 health care enterprises (HCEs) representing 104 individual clinics were asked to report local DRLs for eleven conventional X-ray examinations (including mammography) and nine CT-examinations. The response rate from the clinics was 69% and resulted in 539 individual reported local DRLs in total. Large variations in local DRLs were observed between different clinics for all examination types, ranging from a factor of 3.3 to 61 for conventional coronary angiography and lumbar spine, respectively. Local DRLs exceeding the current national DRLs were observed for all examination types except for conventional coronary angiography. The 75 percentile of the collected local DRLs indicates a need for a downward revision of the national DRLs by 20-60%. A recalculation of the collective effective dose (CED) of 1.1 mSv from 2002 based on the updated dose data resulted in a reduction of the CED by 17%. The impact on patient dose by replacing some conventional X-ray examinations (urography, colon, coronary angiography) with CT-examinations is also briefly discussed.