Institutional CT dose reduction: A retrospective evaluation of dose indices from 2015-2024

Growing attention to radiation risks and dose reduction in CT imaging creates opportunities to present and discuss institutional dose trends and contributing factors.

To provide an evaluation of 10-year trends in CT dose indices (CTDI_vol and DLP) from a multi-site and multi-scanner institution, with the hypothesis that doses have continued to decrease since the last national assessment of medical imaging doses due to scientific and technological improvements.

Data from a radiation dose index management system (Radimetrics, Bayer) were used to analyze diagnostic CT examinations from January 2015 to December 2024, stratified by procedure. Dose indices for the ten most utilized procedures were evaluated over the 10-year period using multivariable linear regression, adjusted for patient weight and age, to estimate annual percent change in dose. Procedures were further stratified by scanner model with quarterly median dose indices for qualitative investigation of trends. To investigate the relationship between dose reductions and image quality, archived annual ACR phantom images were retrieved and evaluated using a semi-automated software (https://ctpro.net/home).

Over the 10-year period, 695,575 diagnostic CT examinations of 235,233 patients were performed on 18 unique scanners (nine models) from three manufacturers. Multivariable linear regression, adjusted for patient weight and age, showed significant decreases in dose indices over time for most high-usage procedures. Model-specific qualitative analyses suggest that acquisition of new scanners, technique changes, and reductions in multiphase imaging were temporally associated with the observed decreases in dose indices. Additionally, the detectability index of low-contrast ACR phantom objects increased on new scanner models despite lower CTDI_vol.

A retrospective review of CT exams demonstrated decreasing CTDI_vol and DLP across multiple frequently performed procedures, coinciding with known technique and technological changes.