Multicentre survey of diagnostic reference levels for single-photon emission computed tomography/computed tomography and PET/computed tomography examinations at Japanese National University Hospitals: a comparative international analysis

Objectives Diagnostic reference levels (DRLs) are essential indicators for optimising medical radiation exposure, although implementation varies by country. In Japan, the Association of Radiological Technologists in National University Hospitals (ARTNU) investigated baseline DRLs for nuclear medicine based on a nationwide survey in 2020. These include the 50 th and 75 th percentile values, providing practical benchmarks for administered activity management. However, comparative insights with Japan DRLs 2025 and international standards remain limited. Methods This nationwide survey, conducted in 2025 across 42 Japanese national university hospitals, examined radiopharmaceutical and computed tomography (CT) administered activity indices in single-photon emission computed tomography/CT (SPECT/CT) and PET/CT (PET/CT) examinations and compared the results with Japan DRLs 2020; Japan DRLs 2025; and international benchmarks from the UK, Europe, USA, Korea, Australia, and Thailand. Japan DRLs 2025 introduced procedural refinements and anatomy-based CT classifications, particularly for PET/CT, aligning with evolving clinical protocols. Results Data on radiopharmaceutical administered activities and CT parameters (CT dose index volume, dose length product) were collected. 18 F-fluorodeoxyglucose-PET protocols predominantly applied 4.0 MBq/kg weight-based dosing, whereas SPECT/CT uses fixed radiopharmaceutical administered activities. CT exposure was adapted according to imaging purpose and anatomical region, frequently achieving low-administered activity operation. Although ARTNU DRLs 2020 remained clinically useful, they exhibited broader administered activity distributions and lack anatomical specificity. Conclusion ARTNU DRLs 2020 should be revised with a follow-up survey to better reflect current practices and align with the increased granularity of Japan DRLs 2025. Japanese institutions have demonstrated concordance with global standards and ongoing administered activity optimisation through technological advancements.