S1433
Interdisciplinary - Other
ESTRO 2026
Efficiency of MR-Enhanced Adaptive Radiation Therapy Ya Wang, Alessandro Mencarelli, Silvia Fabiano, Hubert Gabrys, Serena Psoroulas, Astrid Heusel, Sophie Perryck, Lotte Wilke, Bertrand Pouymayou, Nicolaus Andratschke, Jonas Willmann, Maiwand Ahmadsei, Pawel Drozd, Ina Nilo, Johnny Veenstra, Matthias Guckenberger, Stephanie Tanadini-Lang, Sebastian M Christ Radiation Oncology, University Hospital of Zurich, Zurich, Switzerland Purpose/Objective: Magnetic resonance guided radiotherapy has achieved dosimetrically relevant margin reduction through daily online adaptation based on superior soft-tissue contrast imaging. However, integrated MR-linear accelerator technology is currently too time- and resource-intensive for broad clinical adoption. Within the Adaptive Radiation Therapy Enhanced by Magnetic Imaging Systems (ARTEMIS) Program, our objective was to pioneer a new online-adaptive technique through the seamless integration of a stand-alone MR- scanner with a conventional C-Arm linear accelerator (Linac). Here, we present the feasibility of this novel technique, and report on its implementation and initial learning curve to highlight its potential for improved efficiency. Material/Methods: At the Department of Radiation Oncology at the University Hospital of Zurich, we linked a stand-alone, low-field 0.55T Siemens Free.Max MR-simulator via a CQ Medical Symphony shuttle system with Varian C- Arm Linacs. This technique was enhanced by multiple in-house developed scripts for automation of image processing and plan preparation. Before each fraction, MR sequences are acquired for contouring, along with a synthetic-CT sequence for dose calculation. Contouring of target and organ-at-risk volumes is done by a radiation oncologist, and a new adaptive plan is created by a medical physicist. After plan approval, the patient is shuttled in treatment position from the MR-simulator to the CT-Linac. A verification ConeBeam-CT is performed before treatment delivery. In this first analysis, total patient journey time was assessed. Results: Of the first 218 fractions, 216 (99%) were successfully adapted and delivered as planned, while 2 (1%) were considered not deliverable due to significant anatomical changes that compromised CTV coverage. Median total patient journey time – from imaging start to beam off – was 52 minutes (±15 minutes), ranging from 34 minutes (pelvic lymph node metastasis) to 137 minutes (multiple brain metastases) [Figure 1]. Prostate and pelvic lymph nodes were the most commonly treated sites, with 182 and 23 fractions,
respectively. With increased experience and automation, a notable reduction in average total treatment time was achieved within the first 60 fractions, with the average treatment time across 10- fraction increments decreasing from 70 minutes to 53.5 minutes. [Figure 2].
Conclusion: MR-Enhanced Adaptive Radiation Therapy based on tight integration of a dedicated MR-simulator and CBCT-equipped C-Arm Linac was feasible for almost all patients. After an initial learning curve, the multiprofessional team was able to significantly reduce total patient journey times. By enabling parallelization of imaging, adaptive planning, and delivery, this technique holds great potential to improve patient throughput without compromising treatment quality. Keywords: MR-guided Radiotherapy, Adaptive Radiotherapy
Digital Poster Highlight 984 A Novel Implantable Wireless Dosimeter Enables Real-Time In Vivo Verification for FLASH Radiotherapy Qian Han 1 , Jinyi Lang 2 , Meihua Chen 2 1 School of Medicine, University of Electronic Science and Technology of China, Chengdu, China.
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