CT chest abdomen pelvis doses in Scotland: has the DRL had its day?

Abstract

Objective: This article reports on a pilot study designed to collect dose data representative of current CT chest abdomen pelvis (CAP) practice in Scotland, make any immediately obvious interventions and to identify if the current UK diagnostic reference level (DRL) of 940 mGy cm is still appropriate. The aims are to identify if a Scotland-wide picture archiving and communication system (PACS)-based dose audit of a number of CT examinations is likely to have value in terms of optimization of patient doses and to comment on the significance of the results in terms of future optimization strategies.

Methods: Dose audit of CT CAP examinations at 32 different scanner sites across Scotland using accepted data collection and analysis methods. The minimum sample size was 30.

Results: RESULTS indicate that CT CAP doses are lower than those previously reported (median, 800 mGy cm, 75th percentile 840 mGy cm) but follow a distribution that is not in keeping with the concept of DRLs as presently understood or implemented.

Conclusion: There is value in a PACS-based dose audit project to provide serial snapshots of patient doses as optimization efforts take place and to revise current knowledge about CT doses. In our opinion, the results call into question whether DRLs or the concept of "achievable dose" are suitable for devising optimization strategies once a certain degree of optimization has taken place.

Advances in knowledge: The results reported here suggest that it may be time to take a different approach to optimization, concentrating on tools that are more refined than the DRL, which may have become more of a compliance tool than an aid to optimization.

Figure 1.

Variation of mean dose–length product (DLP) amongst the 32 scanners in the survey. Dotted line is the UK reference level for chest abdomen pelvis examinations.

Figure 2.

The minimum, first quartile, third quartile and maximum dose–length product (DLP) observed at each centre. Dotted line is the UK reference level for chest abdomen pelvis examinations.

Figure 3.

(a) Distribution of mean dose–length product (DLP) before re-audit of scanner. Numbers in bars indicate the number of scanners in each bin. Mean DLP is 780 mGy cm; median DLP, 790 mGy cm; and the third quartile DLP, 837 mGy cm. (b) Distribution of mean DLP following re-audit of scanner 3. Numbers in bars indicate the number of scanners in each bin. Mean DLP is 770 mGy cm; median DLP, 790 mGy cm; and the third quartile DLP, 837 mGy cm.

Figure 4.

Ranking of the dose–length product (DLP) from each scanner. For example, scanner number 14 has the fourth lowest DLP.

Figure 5.

Distribution of mean dose–length product (DLP) following re-audit of scanner 3 and removal of scanners using iterative reconstruction techniques. Numbers in bars indicate the number of scanners in each bin. Mean DLP is 780 mGy cm; median DLP, 800 mGy cm; and the third quartile DLP, 840 mGy cm.