Abstract Background Dual energy CT (DECT) has been demonstrated to improve relative stopping power (RSP) estimation with knowledge of the effective atomic number () and relative electron density (RED). A fast kV switching DECT has been developed and it is necessary to quantify the accuracy of RSP prior to clinical use. Purpose This study evaluates the accuracy of a fast kV switching DECT to calculate , RED, and RSP in tissue‐equivalent phantoms of various sizes. Methods Five different phantoms containing tissue‐mimicking inserts were scanned using the Body Scanning Field of View (SFOV) of a fast kV switching DECT. Head phantoms were rescanned with the Head SFOV. Data from the DECT was used to obtain voxel‐matched and RED volumetric images. From these data, a volumetric image of RSP was calculated for each voxel in the volume. Derived values were compared to their corresponding reference values. Results The largest differences were seen in the low‐density inserts. The mean absolute percent error (MAPE) of and RED was 2.02% ± 2.48% and 1.29% ± 1.86% respectively. RSP MAPE was 1.13% ± 1.17% with the largest difference in sinus material at 6.3%. When comparing DECT‐derived values obtained using Body versus Head SFOV, a paired t ‐test showed no significant difference ( p = 0.61). Conclusions Ultra‐fast kV switching DECT can be used to predict RSP in phantom with an accuracy that is non‐inferior to the range uncertainties commonly used in the clinical environment and has the potential to be used for proton therapy planning.
Wang et al. (2026) studied this question.