ESTRO 2025 - Abstract Book

S3189

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2025

Keywords: CBCT-based adaptive, CT-Sim free, HyperSight

References: [1]

E. Oldenburger, R. De Roover, K. Poels, T. Depuydt, S. Isebaert, and K. Haustermans, “‘Scan-(pre)Plan-Treat’ Workflow for Bone Metastases Using the Ethos Therapy System: A Single-Center, In Silico Experience,” Adv Radiat Oncol, vol. 8, no. 6, Nov. 2023, doi: 10.1016/j.adro.2023.101258. [2] T. Zhuang et al., “Simulation and pre-planning omitted radiotherapy (SPORT): a feasibility study for prostate cancer,” Biomed Phys Eng Express, vol. 10, no. 2, Mar. 2024, doi: 10.1088/2057-1976/ad20aa.

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Digital Poster A year of online adaptive radiotherapy: Evaluating the first year of adaptive treatments on Ethos Mette MB Nielsen, Kenneth F Hofland, Eva Samsøe Clinical Oncology and Palliative Care, Zealand University Hospital, Næstved, Denmark Purpose/Objective: This study retrospectively reviewed dose plans from 86 patients treated with online adaptive radiotherapy (oART) using the Varian Ethos Therapy system during its first year of operation. The aim was to determine if adaptive dose plans were selected over the original scheduled plans and how their plan quality compared. Material/Methods: In the Ethos system, a reference plan is generated before treatment begins and serves as a base for dose plans during adaptive treatments. Each day, the reference plan is recalculated using daily Cone Beam CT (CBCT) imaging (scheduled plan) and reoptimized based on updated CBCT anatomy (adaptive plan). The scheduled or adaptive plan is then selected for delivery. The 86 patients with cancers in the pelvic region (prostate, bladder, rectum, and palliative treatments) treated in the first year of operation were investigated. For this study, adaptive sessions were evaluated weekly, but always with a minimum of three fractions per patient. Two main areas were investigated: