Dosimetric Comparison between Single-energy Computed Tomography and Dual-energy Computed Tomography Relative to Stopping Power Estimation in Proton Therapy

Purpose: The focus of this work was given on the relative stopping power (RSP) using the water equivalent thickness (WET) validation on tissue substitutes and real pig organs, as well as a dosimetric comparison of proton treatment plans between single-energy computed tomography (SECT) and dual-energy computed tomography (DECT)-based dose calculations. Materials and Methods: The CT calibration curve of SECT and DECT data was generated using the stoichiometric calibration method. WET measurement was performed for RSP validation using a Giraffe dosimeter (IBA dosimetry) in various substitute tissues (Gammex) and real pig tissues. The thorax (008A, CIRS) and head (731-HN, CIRS) phantoms were used to generate proton plans. The dosimetric evaluations of SECT and DECT-based plans were performed using the gamma analysis with 1%/1 mm and the dose-volume histograms (DVHs) comparison. Results: For RSP validation of substitute tissues, the largest percent WET difference between measurement and calculation was observed up to 17.9% (4 mm) in lung tissue, using SECT based. In real pig tissues, the average WET difference was 2.3% +/- 2.1% and 2.5% +/- 2.3% for SECT and DECT, respectively. The average gamma passed of about 92.1% for the lung and 96.8% for the head regions was reported. For the lung region, the DVH of the target dose was observed with a higher predicted dose in SECT than in DECT, while results in the head region were in good agreement for both SECT and DECT. Conclusion: The performed dosimetric comparison indicates the dose differences between SECT and DECT. The impact of the CT calibration curve is more pronounced for the thorax region.