ESTRO 2025 - Abstract Book

S3112

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2025

assessed using Structural Similarity Index (SSIM), Root Mean Square Error (RMSE), image uniformity, signal-to-noise ratio (SNR), contrast, contrast-to-noise ratio (CNR), Edge Profile Intensity (EPI), and Edge Profile Standard Deviation (EPS). Treatment plans were created using Eclipse v18.0, applying HyperSight iCBCT_Acuros, Halcyon v3.1 FBP, and planning CT Electron Density (ED) curves. Adaptive replanning included image fusion, target and Organ At Risk (OAR) recontouring, plan re-optimization, and dose evaluation. Dose Volume Histogram (DVH) metrics were compared between HyperSight CBCT, Halcyon CBCT, and CT simulation-based plans. Results: HyperSight CBCT with iCBCT_Acuros reconstruction demonstrated similar Hounsfield Unit (HU) values and image quality to planning CT. SSIM values for HyperSight CBCT and Halcyon v3.1 CBCT compared to CT were 0.608 and 0.473, respectively, with RMSE values of 35.825 and 47.983. SNR values were 27.689 for HyperSight, 62.650 for Halcyon, and 19.810 for CT(Figure 1). For contrast, HyperSight and Halcyon achieved 69.678 and 31.712, while CT yielded 129.760. Image uniformity for CT, HyperSight, and Halcyon were -106.08±6.34, -98.7±12.62, and - 123.12±23.77, respectively. EPI values were -510.180 for CT, -636.598 for HyperSight, and -652.747 for Halcyon. ED curve measurements from HyperSight CBCT were closer to CT simulation ED curves compared to Halcyon v3.1 CBCT. Halcyon HyperSight images provided sufficient quality for treatment planning, with auto-contouring accurately delineating OARs similar to simulated CT plans. Overall, plans using Halcyon HyperSight showed clinically significant results, preserving target coverage and OARs comparable to planning CT results.

Conclusion: This study demonstrates that the newly released HyperSight CBCT has the potential to contribute to more effective offline adaptive radiotherapy. The improved reconstruction algorithm, enhanced HU accuracy, and hardware upgrades increase the precision of treatment plan modifications and dose calculations compared to simulation CT based volumes. This can minimize treatment delays for breast cancer patients with changing volumes during therapy, potentially improving overall treatment outcomes and workflow efficiency.

Keywords: HyperSight, Offline adaptive radiotherapy, CBCT

References: 1. J.R. Gunther, J.A. Moore, C.D. Fuller, K.E. Hoffman, J.M. Balter, ACR benchmark testing of a novel high-speed ring gantry linac kV-CBCT system, Journal of Applied Clinical Medical Physics 21 (2020) 194-200. 2. J.A. Moore, J.M. Balter, J.R. Gunther, K.E. Hoffman, C.D. Fuller, Novel Technology Allowing Cone Beam Computed