Room: AAPM ePoster Library
Purpose: To update provincial diagnostic reference levels (DRLs) established in 2014 for adult CT examinations and to investigate the effect of aging equipment and possible changes in practices.
Methods: This study included the same five CT examinations as the initial survey: head, chest, low-dose chest (LDC), abdomen/pelvis, and chest/abdomen/pelvis (CAP). Dose data, volume CT dose index (CTDIvol) and dose-length product (DLP), were collected from 16 CT scanners. All machines except one, replaced in 2018, were included in the initial dose survey and consequent protocol optimization. Automatic dose modulation options and multislice capability (16–128 detector rows) were available on all scanners. The sample for each protocol included 20 patients of average size. The data were collected for 1560 patients; two hospitals did not have the LDC protocol. Provincial DRLs were calculated as the 75th percentile of patient dose distributions. The differences in doses for the same examination performed five years apart were evaluated using paired two-tailed Student’s t-test.
Results: The updated provincial DRLs expressed as the DLP values were below national DRLs, demonstrating increase by 16% for head and 17% for chest CTs compared to the first survey. The DRLs for abdomen/pelvis scan remained the same, and the values were decreased by 11% and 26% for CAP and LDC examination respectively. The greatest variation by a factor of 3.7 was found for the LDC , however it was an improvement comparing to 5.4-fold from the 2014 data. The differences between the mean values of dose distributions from the first and second surveys were not statistically significant with p>0.05 for all examinations. However, dose increase up to 50% was identified at individual hospitals for different protocols.
Conclusion: Protocol optimization was recommended to the hospitals with the doses above provincial DRLs, especially at the sites that reported dose increase after the initial survey.