Computed Tomography (CT) Dose Can Be Decided by Size of Patient’s T-Shirt

A study examining size-based reference doses for different types of CT examination has found that T-shirt size could provide a perception of dose differences in patients of different body-build.

The study by investigators at the Massachusetts General Hospital (Boston, MA, USA) aimed 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. 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. The investigators analyzed about 0.93 million CT exams from 256 CT facilities in the US. 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, the results showed 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. Based on the findings, the researchers concluded that the novel approach expressing body habitus in terms of T-shirt size was not only simple and intuitive, but also provides a tool to have a perception of differences in dose metrices among patients of different body build.

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