Leveraging Longitudinal ACR CT Dose Index Registry Data to Improve Interpretation of Institutional CT Dose Performance
Abstract
Purpose
ACR CT Dose Index Registry (DIR) benchmarking is commonly reviewed at discrete reporting intervals, but single-interval interpretation can be limited by benchmark shifts, transient variation, or incomplete reference data. This study evaluates how longitudinal DIR analysis may improve interpretation of institutional CT dose performance and protocol triage.
Methods
DIR data from 2020-2025 were analyzed longitudinally for 10 adult CT protocols. For each reporting quarter (n = 21), facility CTDIvol, DLP, and SSDE distributions (25th, 50th, 75th percentiles) were compared with DIR protocol-specific reference percentiles. Inclusion criteria required at least 30 exams per protocol per reporting interval. Dose reference level (DRL) exceedance was defined as a facility metric above the DIR 75th percentile. For each protocol and metric, we computed the frequency of DRL exceedance across intervals and reviewed facility-versus-DIR percentile separation to distinguish sustained protocol performance from registry benchmark shifts. DIR data completeness was assessed by identifying protocols lacking DIR SSDE benchmarks or with limited facility intervals.
Results
Four of ten protocols remained within DRL across all reporting intervals for both CTDIvol and DLP. Sustained DRL exceedances were observed in two of ten protocols. CT Neck with IV contrast and CT C-spine without IV contrast exceeded the DLP DRL in 19 of 21 intervals, and CT Neck with IV contrast also exceeded the CTDIvol DRL in 19 of 21 intervals. With DIR SSDE benchmarks (7/10 protocols), five remained within the SSDE DRL across all intervals. SSDE often remained within DRL despite CTDIvol or DLP exceedances. Higher DLP exceedance rates relative to CTDIvol suggest contributions from scan length, coverage, or multiphase technique.
Conclusion
Longitudinal DIR analysis improves interpretation of institutional CT dose performance, distinguishes persistent exceedances from benchmark shifts, and supports protocol triage by prioritizing protocols with sustained DRL elevation.