S2245
Physics - Intra-fraction motion management and real-time adaptive radiotherapy
ESTRO 2026
adaptive MR-Linac with free-breathing ITV gated delivery. An important ancillary finding of the development was esophagus visibility is enhanced on a T2 image with patients’ ingestion of a mix of pineapple juice/thickening agent prior to acquisition. Motion emulation provided robust assessment of tracking structures without requiring a second patient visit. Emulation predicted the algorithm on average for FB gating would successfully track the target 97.1 ± 1.8% of the time corresponding to a duty cycle average of 86.8 ± 8.4%. Actual average delivery tracking success rate was 93.8 ± 1.6% with observed duty cycle of 87.8 ± 5.8%.
10.1016/j.cmpb.2024.108158SABR consortium. 2019 Jan; https://www.sabr.org.uk/wp- content/uploads/2019/04/SABRconsortium-guidelines- 2019-v6.1.0.pdf Keywords: dose accumulation, respiratory motion, liver SABR Digital Poster 3092 Enabling Personalized Ultra-Fractionated Stereotactic Ablative Radiotherapy (PULSAR) for Ultra-Central Lung Tumors using Motion Management on MR-Linac Justin Visak, Ruiqi Li, Yesenia Gonzalez, Jie Deng, Todd Aguilera, Yuanyuan Zhang, Shahed Badiyan, Mu-Han Lin, Kenneth Westover, Fan Chi Su Radiation Oncology, UT Southwestern Medical Center, Dallas, USA Purpose/Objective This study aims to develop and implement a clinically feasible MR-Linac (MRL) workflow enabling gated, PULSAR for ultra-central lung tumors. The workflow supports a novel clinical trial utilizing motion management and adaptive planning for reduced- margin lung SAbR. A key challenge is selecting suitable candidates for breath-hold (BH) versus free-breathing (FB) delivery, which typically requires an additional visit or risks gating failure during treatment. By integrating motion emulation into MR-simulation, this workflow allows candidate assessment and tracking- structure finalization in a single session, improving both efficiency and patient experience. Material/Methods A multi-disciplinary team of physicians, physicists, and radiation therapists collaboratively developed a MR- simulation protocol to achieve comprehensive motion characterization in one session. Each patient underwent a 4D-CT simulation followed by a 4D-MR incorporating FB, BH, and cine MR acquisitions. Breath-hold coaching was performed outside the MR suite to optimize efficiency and preserve scanner time. Emulation software modeled respiratory and cardiac motion from sim, allowing real-time evaluation of gating surrogates and identification of optimal candidates. Final emulation results with validated targets and gating structures were communicated to the treatment planner for inclusion in the adaptive reference plan. Results The protocol was developed with five volunteer scans and to-date five patients have been enrolled in the trial. All patients with lung internal target volumes (ITV) 1.5-5.0 cm entirely within the 2cm “central zone” or within 1cm of the mediastinum, esophagus or proximal bronchial tree were treated using an
Conclusion This trial establishes a novel gated SAbR framework for ultra-central lung tumors. It demonstrates the feasibility of combining motion emulation and adaptive MR-guided therapy in a streamlined workflow. MR-simulation–based motion emulation eliminates the need for an additional visit, enhancing both patient convenience and clinical efficiency. Successful implementation depends on the coordinated effort of a multidisciplinary team of whose collaboration is crucial for streamlined treatment delivery.
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