Purpose: The purpose of this study was to quantify the accuracy and variability of a proton range estimation based on both single- and dual-energy computed tomography (CT) measurements.
Materials and Methods: Two CT scanners were used to measure both single- and dual-energy scans of four different phantoms. The dual-energy scans were used to create stopping power maps of the phantoms. The maps were subsequently used to calculate a water-equivalent thickness (WET) that was compared against a WET calculated by a treatment planning system (TPS) using the single-energy scans. The two different WET were calculated for each tissue surrogate sample separately, and the results were compared against the properties reported by the phantom manufacturers.
Results: Overall, the dual-energy approach yielded considerably more accurate WET values with root mean square error (RMSE) of about 2%, as compared to the RMSE of about 4.5% for single-energy approach. The accuracy gains were strongly dependent on the material, with bone-like samples exhibiting the strongest improvement. There were no notable differences in the variances of the calculated WET between the single- and dual-energy approaches.
Conclusion: Using dual-energy computed tomography instead of single energy can lead to significant improvements in assessing the WET of especially bony structures. For most soft tissue types, the accuracy gain is less significant.