ESTRO 2025 - Abstract Book

S3169

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2025

Purpose/Objective: The increasing interest in online-adaptive particle therapy (OAPT) resulted in: 1. more centers actively work on OAPT development and clinical implementation; 2. successful first clinical OAPT application using an in-house developed workflow [1]; and 3. launching of first clinical OAPT trial with a commercial workflow [2]. A SWOT (strengths, weaknesses, opportunities, threats) analysis was performed to define common ground and streamline the joint research and implementation efforts. Material/Methods: Within the EPTN (European Particle Therapy Network) adaptive task group, 17 interdisciplinary participants (10 medical physicists, 4 radiation oncologists, 3 radiation therapists (RTT)) from 11 European centres participated in SWOT analysis. Each participant submitted an anonymized SWOT of OAPT; a joint discussion of the collected inputs followed. Afterwards, two subgroups separately analysed Strength/Weakness and Opportunities/Threats associated with OAPT. The combined outcome from both subgroups was merged into a final SWOT analysis, which was critically reviewed by 30 multidisciplinary participants during the EPTN Adaptive Proton Therapy Workshop (October 2024, Vienna, Austria). Results: SWOT addressed 7 major topics: imaging, contours, workflow, resources, RTT-role, dose/outcome and new treatment concepts (Figure 1). No major threats on the technology side were identified, showing that a wide-spread clinical implementation is safe and feasible. Recognized minor threats were related to additional time/costs and the daily delineation consistency. Insufficient cone-beam CT quality, together with the lack of commercial solutions, guidelines and training were major weaknesses hampering widespread availability. The major opportunities lay in superior dose distributions with expected side effects reduction, and in redefinition of RTT-role. OAPT enables not only adapting the plan to density and anatomical changes, but also to better conform dose, thus allowing new treatment schemes, such as dose escalation, isotoxic optimization, ultra-hypofractionation, adaptive fractionation. For an OAPT implementation, ready-to buy workflows, following medical device regulations are needed. An international consensus on an RTT-role, including education, costs and (legal) responsibilities, is necessary. Training, automated workflows and an agreement on intervention levels for radiation oncologists and medical physicists are crucial to define a robust RTT-role. Training programs, adjusted reimbursement schemes and increasing clinical experience are needed for better acceptance of the technology.