• Yousun Ko, Woo Joo Lee, Ji Hoon Park, Hae Young Kim, Ji Ye Sim, Penampai Tannaphai, Kyoung Ho Lee, and for LOCAT Group.
• Program in Biomedical Radiation Sciences, Department of Transdisciplinary Studies, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, South Korea.
• Eur Radiol. 2020 Aug 1; 30 (8): 4573-4585.

ObjectivesTo test whether the difference in sensitivity or specificity between 2-mSv CT and conventional-dose CT (CDCT) for the diagnosis of appendicitis differs across subgroups of adolescents and young adults with suspected appendicitis.Materials And MethodsWe used the per-protocol analysis data of a trial conducted between Dec 2013 and Aug 2016, including 2773 patients (median age [interquartile range], 28 [21-35] years) and 160 radiologists from 20 hospitals. We defined subgroups by sex, body size, clinical risk scores for appendicitis, time of CT examination (i.e., working vs. after hours), CT machines, radiologists' experience, previous site experience in 2-mSv CT, and site practice volume. We drew forest plots and tested for additive or multiplicative interaction between radiation dose and subgroup attributes. If any subgroup had fewer than 200 patients, we considered the results from that subgroup not meaningful.ResultsFor most subgroups, the 95% CIs for the differences in sensitivity and specificity were 4.0 percentage points or narrower and contained the minute overall between-group differences. There was no significant interaction on sensitivity or specificity. A few subgroups, including those of extreme body sizes, high appendicitis inflammatory response scores, and hospitals with small appendectomy volume, were regarded to have insufficient numbers of patients.ConclusionsThere was no notable subgroup heterogeneity, which implies that 2-mSv CT can replace CDCT in diverse populations. Further studies are needed for the subgroups for which we had only small data.Key Points• The minute difference in sensitivity or specificity between the 2-mSv CT and conventional-dose CT (typically 7 mSv) groups were consistent across various patient or hospital characteristics. • These results indicate that 2-mSv CT can replace conventional-dose CT in diverse populations. • Further studies are needed to confirm whether 2-mSv CT can replace conventional-dose CT in patients of extreme body sizes, high appendicitis inflammatory response scores, or hospitals with small appendectomy volume, as those subgroups in our data included limited numbers of patients.

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