Purpose/Objective(s):
Dual-Energy CT (DECT) enhances soft tissue contrast, improving tumor differentiation and delineation in radiation oncology [1]. Integration into treatment planning system (TPS) is only partially established (due to handling multiple reconstructions and reconstruction-dependent CT density calibration tables) and its use in dose calculation is currently explored [2]. Two implementation approaches for dose calculation were investigated: (i) use of an established single-energy CT (SECT) 120 kVp calibration curve, and (ii) application of a dedicated calibration curve for direct electron density reconstruction. The aim was to assess clinical feasibility and quantify dosimetric equivalence to the SECT planning reference.
Materials/Methods:
Imaging was performed using a clinical dual-energy CT scanner. Using an electron density phantom calibration curves were established for electron density reconstructions, and the optimal virtual monoenergetic reconstruction (VMI) energy level was determined to match the SECT 120 kVp calibration curve within the TPS. Dose calculations were conducted on 7 radiotherapy treatment plans using VMAT techniques with 6 MV flattening filter-free beams. Dose distributions derived from (i) VMI at 72 keV (VMIopt) using the SECT 120 kVp calibration curve, and electron density-based reconstructions based on (ii) Rho and (iii) Sd40 were compared against the SECT reference via dose-volume histogram (DVH) parameters and gamma analysis.
Results:
Dose distribution in all reconstructions (VMIopt, Rho, Sd40) showed high agreement in dose calculation accuracy with the SECT reference (see Table 1). Gamma analysis confirmed the high accuracy of DECT-based dose calculations with minimal deviation for Sd40 and slightly greater variability for Rho, but remained within clinically acceptable limits. DVH analysis showed the smallest deviation for Rho and largest deviation for Sd40.
Conclusion:
Dose calculation based on VMI at 72 keV, SECT Sd40 and Rho-based DECT reconstructions yields dosimetrically accurate results for radiotherapy of glioblastoma. These findings enable DECT as a valuable improvement to clinical workflows, combining enhanced contouring accuracy with precise dose calculations. This enables the secure use of DECT data in TPS, with practical implementation depending on the workflow, which can be carried out either through SECT-based (VMIopt) or electron density-based calibration (Rho/Sd40).
References:
[1] Radiother Oncol. 2023 Oct:187:109840
[2] Phys Med. 2026 Jan:141:105702
Table 1: Gamma results and deviations in selected DVH parameters for dose calculations on VMIopt, Rho, and Sd40 relative to the Qr40 reference dose distribution.
