Technical benchmark of a high-speed ring gantry kV-CBCT imager for CBCT-based dose calculation

A CBCT platform (HyperSight (HS)) mounted on an O-ring linac (ETHOS v1.1), is compared with standard CBCT imagers installed on C-arm (TrueBeam v2.7) and O-ring (Halcyon v3.0) linacs, as well as planning CT (pCT). The study focuses on image quality, radiation dose, and dosimetric evaluation (Hounsfield unit (HU) accuracy and dose comparison).

Phantom-based comparisons were performed using default CBCT protocols and reconstruction algorithms available (FDK, iCBCT and iCBCT Acuros CTS). Quantitative image quality metrics (noise, CNR, TTF, low contrast resolution) were studied (IQMetrix software). Radiation dose measurements were compared between CBCT platforms and against manufacturer values.pCT-CBCT HU comparisons were performed on HU-density calibration and anthropomorphic phantoms (Mean Error (ME) and Mean Absolute Error (MAE)). Dosimetric evaluations included relative dose deviations (D50%), and 3D gamma analysis.

The HS imager demonstrated improved image quality and detection efficiency associated with a reduction in radiation doses compared to standard CBCT imagers. HU accuracy improved markedly for HS images reconstructed with iCBCT Acuros CTS yielding MAE(Body) < 29HU except for Head, and |ME (Soft tissue)| <8HU except for Large Pelvis protocol. For density calibration phantom, HU deviations remained within ± 50 HU except for bone densities. Dosimetric comparisons showed dose deviations below 0.5% between pCT and CBCT-based calculations for all protocols using HyperSight with iCBCT Acuros CTS (except for Large Pelvis (0.9%)). Gamma passing rates were consistently above 97.7% for 0.5%/1 mm criteria.

These results confirm the value of 125 kVp HS images reconstructed with iCBCT Acuros CTS for CBCT-based dose calculation.