Clinical Validation of a High-Quality Hypersight Icbct Protocol on a C-Arm Linear Accelerator for Head and Neck Offline Adaptive Planning
Abstract
Purpose
To validate a planning-quality HyperSight iCBCT protocol on a C-arm LINAC for head and neck (HN) offline adaptive planning. By enabling direct use of high-quality CBCTs for re-planning, this approach aims to streamline the offline adaptive workflow.
Methods
By adapting a high-exposure pelvis technique, we developed a dedicated HyperSight iCBCT protocol (HN_PLANNING) for HN adaptive planning on a C-arm LINAC, specifically designed to extend the field-of-view (FOV) to include the shoulders. Imaging dose was measured using a CTDI phantom. To support accurate heterogeneity-corrected dose calculation, a site-specific iCBCT HU-to-density calibration curve was established using an electron density phantom. Longitudinal protocol stability was assessed by analyzing iCBCTs acquired over five consecutive days.
Results
The HyperSight HN_PLANNING protocol demonstrated superior image quality and achieved a significantly expanded axial FOV of 48.51 cm (extendable to 70 cm), compared to the 28.31 cm limitation of the standard Head protocol. This expansion ensured complete inclusion of the shoulder region, preventing truncation during planning. The protocol utilized 884 projections with a total exposure of 1060.8 mAs. The resulting imaging dose was 3.89 cGy; while higher than the standard daily head IGRT dose (0.46 cGy), this is acceptable for a targeted, single-session acquisition for adaptive planning. Longitudinal analysis confirmed HU stability remained within 20 HU of the baseline. The high-speed acquisition produced diagnostic-quality images suitable for contouring and full plan optimization.
Conclusion
The HyperSight system allows the C-arm LINAC to function effectively as a virtual simulator for HN adaptive planning. The HN_PLANNING protocol provides the requisite FOV and HU accuracy for full adaptive planning in a single treatment session, improving workflow and efficiency without compromising dosimetric accuracy.