ESTRO 2025 - Abstract Book

S2987

Physics - Image acquisition and processing

ESTRO 2025

Conclusion: The commissioning of sCT demonstrated the feasibility of an MR-only workflow for stereotactic brain treatments. MR simulations could be successfully performed with an immobilization mask and the head rotations are suitable for CBCT positioning. The non-anatomical components were modeled and included in the sCT for dose calculation. Finally, the re-calculations on sCT showed the presence of outliers above 5%. Future work will focus on fine-tuning the models to limit the outliers. Moreover, the accuracy of the sCT-CBCT match will be verified.

Keywords: synthetic CT, stereotactic, brain

References: [1] Lerner et al, Radiat Oncol (2021) 16:66, https://doi.org/10.1186/s13014-021-01794-6 [2] Pouymayou et al, ESTRO 2024. https://user-swndwmf.cld.bz/ESTRO-2024-Abstract-Book/3890/ [3] Masitho et al, Strahlentherapie und Onkologie (2023) 199:739–748, https://doi.org/10.1007/s00066-023-02090-w

1821

Digital Poster Evaluation of the dosimetric accuracy of Hypersight CBCTp with FDK and Acuros reconstruction algorithms for multiple treatment sites Francesca Dusi, Fabio Busato, Alessandro Testolin, Davide Fiorentin, Edoardo Gozzelino, Mattia Nicoletto, Marco Fusella Radiation Oncology, Policlinico Abano Terme, Abano Terme, Italy Purpose/Objective: Innovative CBCT imaging offers enhanced HU accuracy, large field-of-view and image quality, enabling potential direct treatment planning without additional CT scans. This study aims to evaluate the dosimetric accuracy of HyperSight-CBCT images acquired on a Halcyon v4.0 (Varian), focusing on three anatomical regions (brain, breast, pelvis) and comparing dose calculations on scans reconstructed with two different algorithms: standard FDK and Acuros. Material/Methods: Planning CBCT (CBCTp) were acquired for 10 patients for each site: brain, breast, and pelvis. Treatment plans were optimized on CT images in Eclipse v.18.0, calculated with AcurosXB algorithm. Each plan was recalculated on CBCTp after a rigid registration to the planning CT (pCT) without applying a specific HU-to-mass density calibration curve. To compare dose distributions, the 3D global gamma index was calculated. The study evaluated the dosimetric accuracy of CBCTp, focusing on 2%/2mm gamma pass rates (GPR) with thresholds of 10% and 50% of the prescribed