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

Abstract Purpose Assess the accuracy for quantitative measurements of electron density relative to water ( ρ e / ρ e,w ), effective atomic number ( Z eff ) and stopping power ratio relative to water (SPR w ) 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, CTDI vol , and scanning mode) and different reference materials. Then, electron density ρ e / ρ e,w and atomic number Z eff images were reconstructed, and their values were determined for each reference materials. Based on these two values, SPR w was calculated. Finally, the percent error (PE) against the theoretical values was calculated for reference materials. Results Significant linear relationships ( p ρ e / ρ e,w ( r  = 1.000), Z eff ( r  = 0.989) and SPR w ( r  = 1.000) values. The PE for each reference material varied from –2.0 to 1.2% (mean, ρ e / ρ e,w , from –6.4 to 8.0% (mean, –2.0%) for atomic number Z eff , and from –2.0 to 1.9% (mean, 0.3%) for stopping power ratio SPR w . The mean PE of ρ e / ρ e,w ( Z eff ( w ( p  > 0.85). Conclusions DLCT provides a reasonable accuracy in the measurements of ρ e / ρ e,w , Z eff and SPR w , and could enhance radiotherapy treatment planning and the subsequent outcomes.