Feasibility of Adaptive Replanning with Hypersight-CBCT on a C-Arm Linac
Abstract
Purpose
HyperSight cone-beam CT (HS-CBCT) on C-arm linacs may enable CBCT-based replanning by improving image quality, HU fidelity, and field-of-view (FOV). We evaluated clinical feasibility and dose-recalculation agreement using patient data.
Methods
In this study, two HS-CBCT datasets per treatment course were collected from 40 patients treated on a C-arm linac (clinical trial: NCT06187103, treatment sites: head/neck, breast, thorax, upper gastrointestinal, pelvis). Feasibility was evaluated by (1) determining whether targets, critical OARs, and body contour were contained within the HS-CBCT FOV; (2) qualitative assessment of HS-CBCT image quality for target/OAR contouring; and (3) calculating the clinical plan dose based on HS-CBCT using mode-specific HU-density curves and comparing dose metrics with the planning CT.
Results
In these 40 patients, all target and OAR structures were contained within the HS-CBCT volume. However, 25% of targets and 2.5% of OARs had <2 cm margin to the superior or inferior CBCT boundary. Image quality was considered sufficient for target contouring in 92.5% and for OAR contouring in 87.5% of all patients. In a preliminary subset of 13 pelvis/abdomen cases, target dose metrics recalculated on HS-CBCT generally agreed with the clinical plan within 2%. Across detailed dosimetry subsets (pelvis n=4, thorax n=3, breast n=2), HS-CBCT recalculated OAR metrics were comparable to CT (median deviation <5%, except bladder and rectum in pelvis cases due to inter-fractional filling variations). Thorax results showed stable lung and spinal cord, while esophagus and heart metrics demonstrated greater sensitivity consistent with organ positional changes. These differences may be a consequence of OAR changes rather than HS-CBCT dose calculation accuracy.
Conclusion
HS-CBCT supports accurate CBCT-based dose calculation and shows feasibility for adaptive replanning in patients. Targets and OARs dosimetric metrics agreed generally within a few percentage points between HS-CBCT and planning CT, with site-specific sensitivity to motion and organ filling.