Simulation-Free Expedited Whole Brain Treatments Using Next Generation Cone-Beam Computed Tomography on an O-Ring Adaptive System
Abstract
Purpose
HyperSight cone-beam CT (CBCT) has been validated for direct treatment planning without needing conventional CT simulation. We propose a simulation-free whole-brain radiotherapy (WBRT) workflow using the Ethos online adaptive platform that requires no prior diagnostic imaging and generates clinically acceptable, patient-specific plans within minutes of HyperSight CBCT acquisition.
Methods
The workflow starts with a reference plan created on a CT image of a generic patient, defining the whole brain as the clinical target volume (CTV) and the planning target volume (PTV) as the CTV plus a 1cm margin excluding the orbits. A field arrangement analogous to conventional opposing lateral fields was used, and the plan was optimized in Ethos Treatment Management (V3.0) with a prescription of 30Gy in 10 fractions. Feasibility was evaluated in silico using an Emulator (Varian Medical Systems) with CT images from 12 previous patients. Images were imported into the Emulator and designated as HyperSight CBCT images for direct plan adaptation at the first treatment fraction. Following acceptance of a CBCT image, the whole brain orbits, and lenses were automatically segmented, and patient-specific adaptive plans were generated with dose calculated directly on the HyperSight CBCT using the same field arrangement and optimization objectives as the reference plan. Turnaround time (TAT) from CBCT acceptance to adaptive plan approval, total monitor units (MUs), and dosimetric endpoints were recorded.
Results
Across 12 patients, the average TAT was 4.4±1.2minutes, with total MUs of 935±38. For a single fraction of 3Gy, the average CTV V100% was 98.2±0.1%, PTV D95% was 2.99±0.01Gy, PTV D0.03cc was 3.20±0.01Gy, and mean lens dose was 0.46±0.19Gy.
Conclusion
Validated HyperSight CBCT dose calculations now support simulation-free WBRT workflows that substantially reduce planning time and resource utilization. This approach offers an especially practical solution for urgent palliative scenarios where conventional simulation may delay treatment.