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

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PurposeAssess the accuracy for quantitative measurements of electron density relative to water (ρe/ρe,w), effective atomic number (Zeff) and stopping power ratio relative to water (SPRw) using a dual-layer computed tomography (DLCT) system. Methods and MaterialsA 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 ρe/ρe,w and atomic number Zeff images were reconstructed, and their values were determined for each reference materials. Based on these two values, SPRw was calculated. Finally, the percent error (PE) against the theoretical values was calculated for reference materials. ResultsSignificant linear relationships (p < 0.001) were observed between the measured and theoretical ρe/ρe,w (r = 1.000), Zeff (r = 0.989) and SPRw (r = 1.000) values. The PE for each reference material varied from –2.0 to 1.2% (mean, <0.1%) for electron density ρe/ρe,w, from –6.4 to 8.0% (mean, –2.0%) for atomic number Zeff, and from –2.0 to 1.9% (mean, 0.3%) for stopping power ratio SPRw. The mean PE of ρe/ρe,w (<0.1%), Zeff (<–2.5%) and SPRw (<0.4%) was verified across the variation of scanning parameters (p > 0.85). ConclusionsDLCT provides a reasonable accuracy in the measurements of ρe/ρe,w, Zeff and SPRw, and could enhance radiotherapy treatment planning and the subsequent outcomes.