Cumulative effective dose among 5.6 million CT exams in a multinational radiation dose registry

Abstract Objectives To understand the percentage of patients who exceed a cumulative effective dose of 50 or 100 mSv within 1-5 years of first CT scan, while accounting for data censoring (i.e. considering patients who are no longer being followed in the study and whose unobserved exams may influence the estimates) – a major limitation of prior reports. Methods Retrospective, multi-national study of 5.6 million CT exams in 2.8 million patients from 161 hospitals between 2010-2021. We quantified the percentage of exams with effective doses >50 and >100 mSv, and using survival analysis, projected the percentage of patients with cumulative effective doses above these levels at 1 and 5 years, and identified relevant drivers (e.g., patient size, exam type, country). Results 189,981 (3.4%) of exams were >50 mSv and 14,906 (0.3%) >100 mSv, varying by patient age, size, and exam type. Overall, 13% of average-sized adults and 5% of average-sized children were estimated to accumulate 50 mSv over 5 years (56% and 27% of large-sized adults and children, respectively), whereas 4% of average-sized adults and 1% of average-sized children were estimated to accumulate 100 mSv over 5 years (31% and 13% of large-sized adults and children, respectively). England had a 1.7- to 5-times lower than average percentage of patients exceeding these levelss. Conclusions High cumulative doses were not rare, particularly high in larger patients, and repeat imaging was a strong driver of these exposures. Advances in knowledge When accounting for data censoring, a considerably larger share of patients accumulated high effective dose from CT than has been previously reported, exceeding radiation dose ranges associated with radiation-induced cancer.