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

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Image-Guided Therapy

Background:

• Conventional cone-beam computed tomography (CBCT) systems face challenges with image quality, Hounsfield unit (HU) calibration accuracy, and dose calculation reliability.
• The HyperSight CBCT system on the Halcyon platform aims to overcome these limitations by enhancing HU accuracy, expanding the field-of-view (FOV), and improving overall image quality.

Purpose of the Study:

• To evaluate the dosimetric accuracy of treatment planning using HyperSight CBCT.
• To perform phantom-based dose verification for HyperSight CBCT in a multi-institutional setting.

Main Methods:

• Three institutions utilized the HyperSight imaging system for acceptance testing and calibration.
• Hounsfield unit (HU)-to-density calibration curves were generated using CT scanners and standardized phantoms.
• Treatment plans were created on CT images and recalculated on CBCT datasets (CBCTp and CBCT) for dosimetric assessment.
• Gamma analysis, DVH metrics, ion chamber measurements, and film dosimetry were employed for end-to-end testing using anthropomorphic phantoms.

Main Results:

• Hounsfield unit (HU)-to-density curves demonstrated consistent performance across institutions, with minor variability at higher densities.
• Dosimetric assessment showed differences within 1% for DVH-based metrics when comparing CBCTp and CBCT to CT.
• Gamma analysis yielded high passing rates (≥ 98.5% at 3%/2 mm) for both CBCTp and CBCT.
• End-to-end testing revealed dose agreement within ±4% for CBCT-based plans and ±3% for CT-based plans with film dosimetry.
• Ion chamber measurements showed all dose differences within ±2.3%, with CBCTp and CBCT within ±1.0% of CT.

Conclusions:

• HyperSight CBCT demonstrates accurate dose calculations when properly calibrated, with deviations generally below 2%.
• Phantom-based validation confirms strong agreement with CT-based calculations.
• These findings support the clinical implementation of HyperSight CBCT in adaptive radiotherapy workflows.