Technical note: Phantom-based evaluation of CBCT dose calculation accuracy for use in adaptive radiotherapy

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Image Reconstruction

Background:

• Accurate 3D anatomy is crucial for radiotherapy treatment plan adaptation.
• Current online CBCT workflows involve synthetic CT or fan-beam CT, which can introduce dose calculation uncertainties or process complexity.
• Direct dose calculation on daily CBCT scans can overcome these limitations.

Purpose of the Study:

• To assess the accuracy of dose calculation on CBCT scans acquired using the Halcyon linear accelerator with HyperSight technology.
• To evaluate HyperSight's performance in direct dose calculation for radiotherapy plan adaptation.

Main Methods:

• Utilized HyperSight's improved CBCT reconstruction algorithm featuring enhanced scatter correction, HU calibration, and beam shape adaptation.
• Performed gamma comparisons (2%/2mm, 2%/1mm, 1%/1mm) between doses calculated on HyperSight CBCT and simulation CT in various anatomical phantoms.
• Compared HyperSight's gamma passing rates against the previous Halcyon 3.0 reconstruction.

Main Results:

• HyperSight demonstrated superior performance over Halcyon 3.0, with calculated doses closer to CT-based doses.
• Average gamma passing rates were 92.9% for Halcyon 3.0 and 98.1% for HyperSight across all plans and criteria.
• The new CBCT system showed significant improvements in dosimetric accuracy.

Conclusions:

• HyperSight CBCT images are suitable for direct dose calculation and online plan adaptation in radiotherapy.
• The technology shows promise for improving the accuracy and efficiency of adaptive radiotherapy workflows.
• Feasibility demonstrated for investigated cases including brain, head and neck, lung, breast, and prostate.