Association between waist-to-hip ratio and radiation dose metrics in coronary CT angiography

Directly measured waist- and hip-based indices are less well studied than body mass index (BMI) or CT-derived size measures in coronary CT angiography (CCTA). We examined whether waist-to-hip ratio (WHR) was associated with scanner-reported dose metrics and acquisition extent. This retrospective observational study analyzed anthropometric measurements recorded during the pre-CCTA clinical workflow and retrospectively extracted scanner dose reports from 134 consecutive adults. Cardiac CTDIvol, cardiac-helical dose-length product (DLP), total examination DLP, and CCTA scan length were evaluated. Primary multivariable models included body surface area (BSA), WHR scaled per 0.1-unit increase, age, sex, pre-scan heart rate, and beta-blocker administration. A primary path-based statistical decomposition of the WHR–cardiac DLP association through scan length was adjusted for BSA, age, and sex and used 10,000 bootstrap resamples; a sensitivity decomposition additionally adjusted for pre-scan heart rate and beta-blocker exposure. Among 134 participants, 81 (60.4%) were men and 53 (39.6%) were women; mean age was 52.2 ± 10.6 years. Mean cardiac CTDIvol was 45.7 ± 4.2 mGy, cardiac DLP 708.2 ± 89.0 mGy·cm, total DLP 789.9 ± 97.3 mGy·cm, and scan length 12.0 ± 1.3 cm. WHR was inversely correlated with cardiac DLP (ρ = -0.22, p = 0.011) and scan length (ρ = -0.30, p < 0.001), but not CTDIvol. In adjusted models, each 0.1-unit increase in WHR was associated with 28.3 mGy·cm lower cardiac DLP (95% CI, -50.6 to -5.9; p = 0.014) and 0.67 cm shorter scan length (95% CI, -0.99 to -0.35; p < 0.001). After scan length was added, the WHR coefficient was null (B = 2.1 mGy·cm; p = 0.822), whereas scan length remained strongly associated with cardiac DLP (B = 45.2 mGy·cm/cm; p < 0.001). In the primary decomposition adjusted for BSA, age, and sex, the indirect component through scan length was -30.5 mGy·cm (95% CI, -46.5 to -16.2) and represented 88.9% of the total association; the indirect component was similar in a sensitivity analysis additionally adjusted for pre-scan heart rate and beta-blocker exposure. Pre-scan heart rate was independently associated with CTDIvol (B = -0.25 mGy/bpm; p < 0.001). Higher WHR was associated with shorter CCTA scan length and lower cardiac DLP but not with CTDIvol. The WHR–cardiac DLP association was largely attenuated after accounting for acquisition extent. Because DLP intrinsically incorporates irradiated longitudinal extent, these findings describe a statistical relationship rather than an independently established causal mediator or mechanism, and they do not justify WHR-guided protocol changes without prospective validation.