Quantitative assessment of CBCT image quality metrics and their translation to clinical Art workflow performance in breast cancer patients

BACKGROUND: Online adaptive radiotherapy (ART) relies on cone-beam computed tomography (CBCT) imaging for daily treatment adaptation, but CBCT's physical limitations can compromise contour delineation and dose calculation accuracy. The relationship between image quality metrics and clinical ART workflow accuracy remains unclear. PURPOSE: To investigate the clinical impact of CBCT image quality on ART workflow accuracy in breast cancer patients by comparing contour agreement and dose calculation accuracy between Halcyon and TrueBeam systems, establishing how quantitative image quality metrics affect contour agreement and dose calculation accuracy within the ART workflow. METHODS: Forty breast cancer patients treated with VMAT were equally divided between Halcyon (n = 20) and TrueBeam (n = 20). Phantom-based image quality assessment evaluated HU uniformity, contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR), and modulation transfer function (MTF) using Catphan 504. Planning CT and first-day CBCT images were aligned using deformable registration. AI auto-segmentation generated contours for six structures, evaluated using Dice Similarity Coefficient (DSC) and other geometric metrics. VMAT plans were recalculated on CBCT images using system-specific HU-to-electron density calibration curves for dose-volume histogram, 3D gamma analysis, and dose difference analysis. RESULTS: difference: -0.320 vs. 0.046 Gy, p < 0.001). Although both systems achieved > 99.8% gamma passing rates at 3%/3 mm criteria, stringent 1%/2 mm criteria revealed substantial performance differences (Halcyon: 97.66 ± 1.91% vs. TrueBeam: 90.28 ± 6.51%, p < 0.001). CONCLUSION: Quantitative CBCT image quality metrics, particularly CNR and HU uniformity, directly affect both contour agreement and dosimetric concordance in breast ART workflows. These findings provide quantitative evidence linking CBCT image quality metrics to both contour agreement and dose calculation accuracy within the ART workflow.