Investigation on Accuracy of Stopping Power Ratio Prediction Based on Spectral CT

Purpose In proton radiotherapy, the precise estimation of a beam profile is essential for improving the dose deposited in the target tissues in clinical treatment planning. An accurate beam range is determined based on the stopping power ratio (SPR) of the tissues and beam energy. This study investigated the potential of a spectral computed tomography (CT) based on a fast kV-switching dual-energy technique to predict the SPR for proton radiotherapy. Methods We scanned 11 types of tissue equivalents (CIRS phantom) and derived the electron density and the effective atomic number from spectral CT to predict the SPR using the method proposed by Hunemohr et al. We investigated the influence of energy pairs on SPR prediction accuracy and compared three scan modes on spectral CT and single-energy CT (SECT). Results The prediction accuracy of SPR on spectral CT was within 0.79% (except for the lungs). The divergence of the lungs exhibited a defect in the phantom. Meanwhile, we revealed that the energy pairs had a negligible effect on SPR estimation. Additionally, we demonstrated that the gemstone spectral imaging (GSI) mode on spectral CT owned the most accurate prediction compared with the mono-energetic mode on spectral CT and the normal mode on SECT. Conclusion Spectral CT in GSI mode was shown to be an effective instrument for predicting SPR, which contributes to the accurate prediction of SPR using spectral CT and expands the application of spectral CT.