Multi-institutional validation of hypersight CBCT-based dose calculation on O-ring linacs

Conventional cone-beam computed tomography (CBCT) systems are limited by suboptimal image quality, inaccurate Hounsfield unit (HU) calibration, and reduced reliability for dose calculation. HyperSight CBCT on the Halcyon platform offers improved HU accuracy, expanded field-of-view (FOV), and enhanced image quality.

This study aimed to assess the dosimetric accuracy of treatment planning using HyperSight CBCT through phantom-based dose verification.

This study included three institutions equipped with the HyperSight imaging system on the Halcyon platform, with all procedures performed after acceptance testing and calibration. Each institution generated HU-to-density calibration curves using computed tomography (CT) scanners and standardized phantoms, and corresponding CBCT for planning (CBCTp) scans were also acquired. Additional CBCTp scans were acquired using a consistent phantom model (062 M) across the three institutions. Reference treatment plans were created on CT images and transferred to CBCTp and CBCT datasets for dose recalculation using identical parameters. Dosimetric assessment included gamma analysis and comparisons of DVH-based dosimetric metrics for relevant regions of interest (ROIs). End-to-end testing with an anthropomorphic phantom was performed using ion chamber measurements and film dosimetry at brain, bone, and thorax locations.

HU-to-density curves showed consistent behavior across institutions, with larger variability only at higher densities. CBCTp calibrations agreed well with vendor references. DVH-based dosimetric metrics showed differences generally within 1% for both CBCTp and CBCT when compared with CT. Across institutions, gamma analysis of both CBCTp and CBCT yielded high passing rates (≥ 98.5% at 3%/2 mm). End-to-end testing with film dosimetry showed that CBCT-based plans agreed with measured doses within ± 4%, while CT-based plans were within ± 3%. Ion chamber measurements showed all dose differences within ± 2.3%, with both CBCTp and CBCT within ± 1.0% of CT.

HyperSight CBCT provides accurate dose calculations when properly calibrated. Phantom-based validation demonstrated sub-2% deviations and strong agreement with CT, supporting its clinical use in adaptive radiotherapy.