S2172
Physics - Inter-fraction motion management and daily adaptive radiotherapy
ESTRO 2026
satisfaction. A fully automated workflow produced comparable or slightly improved dosimetry, particularly for the heart, and if implemented could lead to reduced overall treatment time. References: 1. Weststrate T, Bruijs LAP, van Dijk IWEM, et al. 960 Dosimetric advantages of daily online adaptive radiotherapy in patients undergoing chemoradiotherapy for esophageal cancer. Radiother Oncol. 2025;206:S3091-S3093. doi:10.1016/S0167- 8140(25)04423-82. Bachmann N, Schmidhalter D, Corminboeuf F, et al. Cone Beam Computed Tomography-Based Online Adaptive Radiation Therapy of Esophageal Cancer: First Clinical Experience and Dosimetric Benefits. Adv Radiat Oncol. 2025;10(1):101656. doi:10.1016/j.adro.2024.101656 Keywords: Online-adaptive, Esophageal, automation Validation of CBCT-based synthetic CTs for adaptive workflow optimization in proton and carbon ion therapy Erica Simeone 1 , Alessandro Vai 1 , Silvia Molinelli 1 , Alfredo Mirandola 1 , Stefania Russo 1 , Giuseppe Magro 1 , Vittoria Pavanello 1,2 , Barbara Vischioni 3 , Luca D'Ambrosio 3 , Guido Baroni 4,5 , Mario Ciocca 1 , Ester Orlandi 3,6 1 Medical Physics, National Center for Oncological Hadrontherapy, Pavia, Italy. 2 Physics, IUSS - School for Advanced Studies, Pavia, Italy. 3 Radiation Oncology, National Center for Oncological Hadrontherapy, Pavia, Italy. 4 Bioengineering Unit, National Center for Oncological Hadrontherapy, Pavia, Italy. 5 Electronics, Politecnico Di Milano, Milano, Italy. 6 Clinical, surgical, Diagnostic and Pediatric Sciences, University of Pavia, Pavia, Italy Purpose/Objective: Particle therapy relies on up-to-date anatomical information to ensure accurate dose delivery, as small anatomical changes can affect particle range. Repeated CT scans increase workload and patient exposure. Synthetic CTs (sCTs) from CBCTs may enable more efficient offline adaptive workflows. This study assessed the feasibility and accuracy of CBCT-derived sCTs in head and neck patients treated with protons and carbon-ions. Material/Methods: Mini-Oral 3919 sCTs were generated using the Virtual CT algorithm available in RayStation (RaySearch Laboratories, Stockholm, Sweden, version 11B).A preliminary evaluation in-silico was performed on a CIRS phantom, delivering monoenergetic beams on each individual plug. The calculated distal 90% range was compared between the reference CT and the sCT for both proton
workflow significantly reduced heart exposure (DFE- mean=0.44 vs 0.41Gy p=0.001; VFE-30Gy=7.4% vs 5.5%, p<0.001). Patients did not perceive their time at the department as long (median=1, interquartile-range [IQR]=1-2) and were willingness to undergo oART again if necessary (median=5, IQR=4-5).
Conclusion: The clinical oART workflow provides robust target coverage, optimized OAR sparing, and high patient
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