Evaluation of a fast kV switching dual energy CT in deriving relative stopping power using tissue equivalent phantoms of various sizes.

BACKGROUND: Dual energy CT (DECT) has been demonstrated to improve relative stopping power (RSP) estimation with knowledge of the effective atomic number ( Z eff ${Z_{{\mathrm{eff}}}}$ ) 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 Z eff ${Z_{{\mathrm{eff}}}}$ , 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 Z eff ${Z_{{\mathrm{eff}}}}$ 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 Z eff ${Z_{{\mathrm{eff}}}}$ 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.