A Decade of Change in Adult CT Radiation Doses: 2025 U.S. Diagnostic Reference Levels.

Background Diagnostic reference levels (DRLs) and achievable doses (ADs) are intended to reflect contemporary CT practice, but national benchmarks are updated infrequently. Purpose To update U.S. national adult CT DRLs and ADs derived from 2025 data and to demonstrate a scalable, acquisition-level, size-normalized benchmarking framework for generating timely and clinically relevant national benchmarks. Materials and Methods This retrospective observational study analyzed adult CT acquisitions performed between January 1 and December 31, 2025, across U.S. facilities using the Imalogix radiology optimization platform. The 10 most common adult CT examination categories, matching the 2014 benchmark study, were mapped using standardized RadLex Playbook identifiers. Dose metrics (volume CT dose index [CTDIvol] and dose-length product [DLP]) were extracted from dose structured reports and normalized at the acquisition level. Patient size was quantified using attenuation-based water-equivalent diameter from axial images with automated truncation correction, and size-specific dose estimates (SSDE) were calculated using standardized American Association of Physicists in Medicine task group methods. ADs and DRLs were calculated as the 50th and 75th percentiles, respectively, of facility-level median dose distributions per International Commission on Radiological Protection Publication 135 and compared with 2014 U.S. benchmarks. Results A total of 5 234 285 CT acquisitions performed in 2 802 416 adults (mean age, 58.1 years ± 19.7 [SD], 1 575 029 female) at 592 U.S. facilities were analyzed, representing a nearly fourfold larger sample than the 2014 study. Relative to 2014, national CTDIvol ADs and DRLs decreased by 9.3% and 21.8%, respectively. The largest reductions were observed for chest examinations with contrast material (31.2%), whereas smaller reductions were observed for head examinations without contrast material (3.5%). Dose metrics demonstrated consistent size dependence across all torso examinations. Conclusion U.S. adult CT radiation doses have decreased substantially over the past decade. This acquisition-level, size-normalized methodology enables near-real-time generation of national DRLs and ADs for modern CT dose benchmarking. © RSNA, 2026 Supplemental material is available for this article. See also the editorial by McCollough in this issue.