Evaluation of Stopping Power Ratio Calculation Using Dual-energy Computed Tomography With Fast Kilovoltage Switching for Treatment Planning of Particle Therapy.

Background/aim: This study evaluated the calculation accuracy of the stopping power ratio (SPR) using dual-energy computed tomography with fast kilovoltage switching (FKSCT) for particle therapy.
Materials and Methods: A tissue characterization phantom with various reference materials was scanned to obtain single-energy computed tomography (SECT) images and generate virtual monochromatic images at 77 keV (VMI _77keV ) and 140 keV (VMI _140keV ), water density (WD) images, and effective Z (Z _eff ) images. For SECT, VMI _77keV and VMI _140keV lookup tables were generated to convert the measured Hounsfield value into the theoretical SPR for a normal phantom size. Subsequently, the reference materials were scanned in small and large phantoms. The SPR was calculated using the lookup tables of SECT (SPR _SECT ) images, VMI _77keV (SPR _77keV ), and VMI _140keV (SPR _140keV ), and it was derived from the WD and Z _eff (SPR _WD ).
Results: In the normal-sized phantom, the overall mean difference between SPR _WD and theoretical SPR was -0.3%, and remained below 2% for most reference materials. For the large phantom, the overall mean absolute difference for SPR _140keV (3.0%, p=0.006) and SPR _WD (3.2%, p=0.002) for the reference materials was significantly lower than that for SPR _SECT (5.9%). For the small phantom, a significant reduction in the mean difference in the SPR calculation was observed in SPR _77keV (1.0%, p=0.001) and SPR _140keV (1.1%, p=0.013) compared with SPR _SECT (2.2%).
Conclusion: VMI _140keV generated using FKSCT significantly improves the estimation accuracy of SPR compared with SECT. Thus, FKSCT may be used to improve the dose calculation accuracy for treatment planning of particle therapy.
(Copyright © 2022 International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)