Hypersight CBCT–Based Simulation on Ethos: Workflow Development and Dosimetric Assessment
Abstract
Purpose
To evaluate the feasibility of HyperSight CBCT–based radiotherapy planning on the Varian Ethos v2.0 platform and to develop a clinically deployable simulation workflow that overcomes current system limitations.
Methods
The Ethos v2.0 platform requires an existing treatment plan to access a patient record. To address this, we developed EthosSimHelper, a custom application that generates placeholder images, structures and plans and automates their export to Eclipse, enabling a streamlined and reproducible simulation workflow. The SNC Advanced Electron Density and QUART phantoms were scanned using HyperSight CBCT on Ethos and conventional CT on a Siemens X.ceed simulator and HU values were compared. A VMAT plan was generated on the planning CT in Eclipse (v15) using the Acuros XB algorithm and recalculated without re-optimization on HyperSight CBCT for both phantoms and two pelvic patient cases. Relative and absolute dose differences were assessed.
Results
EthosSimHelper successfully enabled a smooth Ethos simulation workflow with a clear and easily implemented procedure for clinical staff. HyperSight CBCT showed HU agreement within 50 HU for soft tissue, with maximum deviations below 120 HU in high-density regions. Phantom studies demonstrated mean dose differences below 1.8% for PTVs and 2.5% for OARs. In patient cases, target and OAR dose differences were under 1.5% and 3.5%, respectively. DVH and isodose comparisons demonstrated strong dosimetric agreement between CT- and CBCT-based plans.
Conclusion
HyperSight CBCT–based planning on Ethos produces dosimetric accuracy within clinically acceptable tolerances. By enabling direct simulation and planning on the Ethos platform, this workflow expands clinical flexibility and reduces time to treatment, particularly in high-throughput or resource-constrained settings.