A quantitative comparison of data evaluation methods to derive diagnostic reference levels for CT from a dosimetric...

To compare simple and sophisticated evaluation strategies for CT dosimetry surveys with focus on DRLs.

Based on data from a nationwide Austrian CT dose survey, different evaluation strategies are compared. These were pooled data analysis, weight banding excluding data from patients with weights outside ±20 kg of the standard weights (70 and 75.6 kg representing the actual average weight), and a regression method estimating DLP probability distributions for the standard patient for each scanner before calculating quartiles.

In the abdomen and chest region, weight restriction (-9% and -4% around 70 and 75.6 kg, respectively, compared to pooled data analysis) and statistically weighting each scanner equally (-9%) have the largest effect on DRLs derived. However, the difference in 3rd quartiles calculated using weight restriction alone compared to regression analysis is relatively small (<1% for 70 ± 20 and -6% for 75.6 ± 20 kg, respectively, trunk region). In the head/neck region the effect of weight restriction is less than in for scans of the trunk (-1.3% and -0.2%, respectively); the most prominent changes resulted from excluding scanners with less than 10 patient cases (-5%), and equally weighting scanners rather than cases (-3%).

For adult CT examinations (different to a paediatric survey), quite simple evaluation strategies yield results very comparable to those from sophisticated strategies.