T-shirt size as a classification for body habitus in computed tomography (CT) and development of size-based dose reference levels for different indications.

PURPOSE: To examine the impact of patient size on dose indices and develop size-based reference levels (50th and 75th percentiles) for 20 body CT exams for routine and organ-specific clinical indications. METHODS: Based on effective diameter estimated from adult body CT, each acquisition was classified into T-shirt size as XXS, XS, S, M, L, XL, and XXL. Radiation dose indices for each size and each exam type were correlated. RESULTS: About 0.93 million CT exams from 256 CT facilities in the United States were analysed. Taking T-shirt size M as a reference, the CTDIvol for other sizes were: XXS (∼60%), XS (∼65%), S (∼75%), L (∼130%), XL (∼165%), XXL (∼210%), or grossly small patients received about 60% of the dose as compared to M sized patients and XXL required doubling the dose. Taking ratio of the dose indices of the largest to smallest size, it was evident that SSDE variation was much less (about 50%) than that in CTDIvol, but there was still nearly 40 to 220% variation in SSDE across the range of t-shirt sizes. The 50th and 75th percentile values are presented for CTDIvol, SSDE and DLP for each of the 20 CT exams and for each of the seven T-shirt sizes. CONCLUSIONS: A novel approach expressing body habitus in terms of T-shirt size is not only simple and intuitive, but it also provides a tool to have a perception of differences in dose metrices among patients of different body build.