2210 - Evaluation of Dual-Energy CT for Accurate Dose Calculation in Stereotactic Radiotherapy of Brain Metastases

Purpose/Objective(s): Dual-Energy CT (DECT) enhances soft tissue contrast, improving tumor differentiation and delineation in radiation oncology. While its role in visualization brain metastases is established [1], its use in dose calculation remains underexplored. Treatment planning systems (TPS) typically rely on Single-Energy CT (SECT)-derived patient density models using a single calibration curve, but handling multiple calibration curves within the TPS is challenging. This study evaluates whether DECT reconstructions can replicate SECT-based dose distributions in stereotactic photon radiotherapy of brain metastases. Two reconstructions are assessed: (1) Virtual Monoenergetic Imaging (VMI_opt) at an optimized energy to maintain SECT calibration compatibility, and (2) Rho reconstruction, which directly maps electron density.

Materials/Methods: Imaging was performed using a CT scanner and an advanced electron density phantom. Calibration curves were established for electron density reconstructions, and the optimal VMI energy level was determined to match the SECT 120 kVp calibration curve within the treatment planning system. Dose calculations were conducted on 24 stereotactic radiotherapy plans using non-coplanar, 3D-conformal techniques with 6 MV flattening filter-free beams, comparing SECT Qr40 reconstructions with optimized VMI and Rho reconstructions via Dose-Volume Histogram (DVH) parameters and gamma analysis.

Results: The optimal VMI energy level was identified as 72 keV, aligning closely with the standard SECT calibration. VMI-based dose calculations exhibited minimal deviation from SECT, with average differences of 0.27%, 0.37%, and 0.41% for D95%, D98%, and D99%, respectively. Maximum deviations remained below 1.89%. Rho-based reconstructions displayed slightly greater variability, but remained within clinically acceptable limits, with average deviations of 0.75%, 0.92%, and 1.02% for the same DVH parameters. Gamma analysis confirmed the high accuracy of DECT-based dose calculations, with VMI achieving pass rates above 99.6% and Rho exceeding 99.1% using a 1%/1mm gamma criterion.

Conclusion: Both VMI at 72 keV and Rho-based DECT reconstructions provide accurate dose calculations for stereotactic radiotherapy of brain metastases. VMI showed minimal deviations, enabling seamless TPS integration, while Rho enabled direct electron density mapping. These findings support DECT as a valuable addition to clinical workflows, combining improved contouring accuracy with precise dose calculations. The choice between methods depends on workflow constraints and risk management. Importantly, neither method requires an additional SECT scan, avoiding unnecessary radiation exposure.