S2170
Physics - Inter-fraction motion management and daily adaptive radiotherapy
ESTRO 2026
images for each control-point could monitor patient anatomical changes to improve the precision and timeliness of offline ART decision-making and to support more adaptive, patient-specific radiotherapy workflows. Material/Methods: A retrospective analysis was conducted on six patients with head and neck (HN) cancer treated with volumetric modulated arc therapy (VMAT). All selected patients underwent replanning after significant anatomical changes identified during clinical review. An EPID image prediction model, implemented within the Watchdog system, was used to generate predicted EPID transit images vs control-point for original treatment plan for original and rescan CT datasets. For each CT dataset, spinal cord and PTV (PTV52, PTV55, PTV70, depending on prescription) structure projections onto the EPID predicted images were generated for each control-point to monitor the change in fluence signal for these structures. Results: The method showed a high sensitivity and angular sensitivity to patient anatomical changes. A consistent increase in signal intensity was observed in patients with weight loss compared to their original plans.
Conclusion: LoP-treatments resulted in significantly smaller PTV- volumes unless the total-plan was selected, potentially improving OAR-sparing. Online image review times were initially longer for LoP-treatments; however, the time decreased with experience. Preliminary dose analysis demonstrated sufficient target coverage with clear value of using LoP. An adaptive strategy will further improve target coverage, potentially enabling margin reduction. Keywords: Library of plans, Cervical cancer, Dose tracking Control-point resolved monitoring of patient anatomical changes for adaptive radiotherapy Natalie Kong 1 , Bradley Beeksma 1 , John Simpson 2 , Jose A Baeza-Ortega 2 , Suhuai Luo 2 , Stuart Szwec 2 , Corie-Lee Smith 2 , Peter B Greer 1,2 1 Radiation Oncology, Calvary Mater Newcastle, Newcastle, Australia. 2 School of Information and Physical Sciences, The University of Newcastle, Newcastle, Australia Purpose/Objective: Adaptive radiotherapy (ART) allows modification of a treatment plan to account for anatomical or Digital Poster 3870 physiological changes that occur during a radiotherapy course. While hardware and software to calculate daily delivered dose are being developed current clinical ART workflows are time consuming and performed at arbitrary frequency[1].This study aims to investigate whether a real-time EPID transit verification system (Watchdog) that compares predicted vs measured
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