S1925
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
reconstruction algorithm, is equipped with the AcurosKV (AKV) for improved scatter correction. In 2023, the HyperSight flat panel (HS) was released, twice the size of the previous one and sold as a CT-like imaging system for online adaptive radiotherapy (oART). Continuing the effort of previous authors, the purpose of this study is to evaluate the performance of both imaging systems and reconstruction algorithms to assess their suitability for dose calculation. Material/Methods: The Cheese phantom with 12 inserts of varying density (ranging from 0.28 to 1.825g/cc) and an anthropomorphic phantom were scanned with the Pelvis 125 kV CBCT protocol in 5 scenarios with varying scatter and lateralization conditions. Those measurements were all performed on the same machine to avoid any bias. Intensity Modulated Radiotherapy plans were generated for each scenario on a planning CT scan (pCT) and recalculated on the Halcyon 2.0 CBCT images reconstructed with AcurosKV (Halcyon AKV), the Hypersight CBCT images reconstructed with (HS w/ AKV) and without AcurosKV (HS w/o AKV). The difference in mean HU between the pCT and each CBCT was evaluated for each insert in the Cheese phantom and for each PTV in the anthropomorphic phantom. The Dmean, D2%, D50%, D95%, and D98% were compared on both phantoms. Results: Regarding the CBCT scans of the anthropomorphic phantom, the average (±SD) of the difference in mean HU between pCT and CBCT was larger for HS w/o AKV
Conclusion: This study shows that the key factor for accurate CBCT dose calculation is its reconstruction algorithm, independent of the imager used. Reconstruction algorithm AcurosKV opens the path for accurate offline replanning on CBCT. In addition, it paves the way for oART with direct CBCT dose calculation using the previous, most common, imaging system whose use for oART dose calculation on CBCT is currently restricted by the vendor. Keywords: CBCT, Hypersight, Dose calculation Digital Poster 3225 AutoTPS: Automated back-up radiotherapy planning across treatment machines Poppy Nikou 1 , Daniel Sandys 1 , Miranda Frizzelle 1 , Ruairidh Howes 1 , Molly Munro 1 , Sarah Osman 1,2 , Catharine Clark 1,3 1 Dept of Radiotherapy Physics, University College London Hospital, London, United Kingdom. 2 National RTQA, Radiotherapy Trials Quality Assurance (RTTQA) Group, London, United Kingdom. 3 Dept of Medical Physics and Biomedical Engineering, University College London, London, United Kingdom
(37,73HU±30,6HU) than for Halcyon AKV (- 7.09HU±13.87HU) and Hypersight w/ AKV
(2.24HU±16.54HU). The maximum difference in mean HU between Halcyon AKV and Hypersight w/ AKV was <23.6HU. The average dosimetric difference from the pCT was <1% for all CBCTs but smaller differences were found with CBCTs reconstructed with AcurosKV (D50%: 0.06%±0.27% for HS w/ AKV CBCT and D50%: 0.07%±0.39%for Halcyon AKV CBCT). A similar trend of HU and dose difference between the pCT and CBCT was observed in the scans of the Cheese phantom.
Purpose/Objective: Treatment planning is one of the most time-
consuming steps in radiotherapy, involving structure creation, plan configuration, DVH objective setting, and dose optimization. At our institution, patients planned on specialized machines (such as proton or Halcyon units) often also require back-up plans on standard TrueBeam systems, adding to the workload. To accelerate this, automated treatment planning software (AutoTPS) was developed to generate plans with minimal user input. Material/Methods: AutoTPS was developed using ESAPI in Eclipse v16.1 and RapidPlan v16.1. Users select the treatment machine and anatomical site, after which the system can automatically generate the required optimization structures. Configuration files store machine- and site- specific information and link the RapidPlan model,
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