Estimation of electron density, effective atomic number and stopping power ratio using dual-layer computed tomography for radiotherapy treatment planning

Purpose: Assess the accuracy for quantitative measurements of electron density relative to water (P-e/P-e,P-w), effective atomic number (Z(eff)) and stopping power ratio relative to water (SPBw) using a dual-layer computed tomography (DLCT) system. Methods and Materials: A tissue characterization phantom was scanned using DLCT with varying scanning parameters (i.e., tube voltage, rotation time, CTDIvol, and scanning mode) and different reference materials. Then, electron density P-e/p(e,w) and atomic number Z(e)(ff) images were reconstructed, and their values were determined for each reference materials. Based on these two values, SPA(w) was calculated. Finally, the percent error (PE) against the theoretical values was calculated for reference materials. Results: Significant linear relationships (p < 0.001) were observed between the measured and theoretical p(e)/ p(e,w) (r = 1.000), Z(e)(ff) (r = 0.989) and SPA(w) (r = 1.000) values. The PE for each reference material varied from -2.0 to 1.2% (mean, < 0.1%) for electron density P-e/P-e,P-w, from -6.4 to 8.0% (mean, -2.0%) for atomic number Ze(ff), and from -2.0 to 1.9% (mean, 0.3%) for stopping power ratio SPRw. The mean PE of P-e/P-e,w ( < 0.1%), Z(e)(ff) ( < -2.5%) and SPA(w) ( < 0.4%) was verified across the variation of scanning parameters (p > 0.85). Conclusions: DLCT provides a reasonable accuracy in the measurements of P-e/P-e,P-w, Z(e)(ff) and SPRw, and could enhance radiotherapy treatment planning and the subsequent outcomes.