Author: Njood Alsaihati, Francesco Ria, Ehsan Samei, Justin B. Solomon, Martina Talarico, Jered Wells 👨🔬
Affiliation: Duke University, Clinical Imaging Physics Group, Department of Radiology, Duke University Health System 🌍
Purpose: Radiation dose and associated risk in X-ray imaging is principally informed by patient size, further used in Computed Tomography (CT) to achieve prescribed image quality levels through tube current modulation (TCM). Yet patient size is not a scalar metric given the nature of human body habitus. The purpose of this study was to evaluate the predictive potential of different patient size metrics for CT radiation risk.
Methods: Six virtual anthropomorphic phantoms (XCAT) representing differing body habiti, were imaged using a scanner-specific simulator (DukeSim) modeling a clinical CT system (SOMATOM Definition Flash, Siemens). Chest CT were simulated with TCM quality reference mAs (QRM) at 55, 110, and 165 mAs. For each phantom organ doses were estimated using a Monte Carlo program to derive effective dose (E). Weight, BMI, and ellipticity ratio were calculated, along with effective diameter (DE) and water-equivalent diameter (DW) for each slice and reported as average, median, and center values across the imaging volume. Linear regression analysis was applied to assess the correlation of E with various size metrics.
Results: A positive relationship was observed between patient size metrics and E across all simulated conditions. DE, DW, and weight showed the best correlation with E, with maximum R2 values of 0.64, 0.57, and 0.59, respectively. BMI exhibited lower R2 values: 0.47, 0.36, and 0.21 at QRM of 55, 110, and 165 mAs, respectively. Ellipticity ratio had the weakest predictive power for E.
Conclusion: In the context of Siemens TCM chest studies performed on normal-to-overweight adults, patient diameter and weight are modest predictors of radiation risk. Risk predictability varied within the same patient size metric as a function of patient ellipticity and QRM, reflecting their impact on TCM performance. Radiation risk in CT is best done using individualized methods, or mindful use of best predictive measurands of size.