Identifying optimal dose head CT acquisition techniques through cluster analysis from 904,209 scans.

OBJECTIVES: To identify clinically established and frequently utilized routine head computed tomography (CT) acquisition techniques in children and adults that achieve lower radiation. MATERIALS AND METHODS: The level of the analysis is at the CT scan (series) level. CT acquisition parameters were analyzed from a large, international CT dose registry. Scans were analyzed separately in adults and children, and by approach (helical or axial), resulting in four strata. K-means clustering, an unsupervised machine learning approach, assigned the scans into clusters based on the following acquisition parameters: Tube current, voltage, collimation, scan length, and for helical scans, pitch. Effective patient diameter, unadjusted and patient size-adjusted dose-length product (DLP), and volume CT dose index (CTDIvol) were compared across clusters. RESULTS: 864,182 CT scans in adults and 40,027 scans in children between January 1, 2015, and March 11, 2021, were included in the analysis. Scans were classified into seven helical and six axial clusters in adults, six helical and four axial clusters in children. In all four strata, the mean size-adjusted DLP varied more than two-fold, and up to 3.4-fold, across the clusters. For example, for adult helical scans (the largest strata), the size-adjusted DLP ranged from 372 mGy·cm to 998 mGy·cm (relative dose 2.7) across clusters. Clusters with the lowest radiation generally utilized lower tube current and voltage, but protocols utilized various approaches to result in lower doses. CONCLUSION: There remains a large variation in the radiation dose within frequently used head CT acquisition techniques. Clustering analysis enables identifying protocols with lower doses. KEY POINTS: Question Is there a large variation in the doses used for routine head CT, and can we identify best-practice, lowest dose approaches for scanning? Findings Across each stratum (adult/pediatric, helical/axial), the mean size-adjusted DLP varied by more than two-fold across the CT scan clusters, reflecting significant differences in radiation. Clinical relevance Many routine head CT acquisition techniques use excessive radiation doses. Standardizing practice to the lowest dose clusters would result in significant reductions in patient dose.