S1255
Clinical - Urology
ESTRO 2026
Results: Daily plan adaptation significantly improved target coverage. Compared to on-adapted base plans recalculated on the daily anatomy, the clinical target volume (CTV) receiving 100% of the prescribed dose (V100%) increased on average from 87% to 93.5%, and the planning target volume (PTV) V100% improved from an average of 89.4% to 97.8% (Figure 1).
al. International Journal of Radiation Oncology, Biology, Physics. 20256.Murthy et al. ASTRO Annual Meeting 2025 (conference proceeding) Keywords: Bladder cancer, adjuvant radiotherapy, cystectomy Digital Poster 3213 MRI-enhanced online adaptive stereotactic body radiotherapy improves target coverage and reduces rectal dose in localized prostate cancer Irma Telarovic, Silvia Fabiano, Hubert S. Gabry ś , Lotte Wilke, Bertrand Pouymayou, Astrid Heusel, jonas willmann, Reinhardt Krcek, Maiwand Ahmadsei, Ricarda S. Guninski, Serena Psoroulas, Ya Wang, Alessandro Mencarelli, Pawel Drozd, Sophie Perryck, Nicolaus Andratschke, Stephanie Tanadini-Lang, Matthias Guckenberger, Sebastian M. Christ Department of Radiation Oncology, University Hospital and University of Zurich, Zurich, Switzerland
Purpose/Objective: Magnetic resonance imaging (MRI)-guided
radiotherapy enables precise visualization of daily anatomy and on-table plan adaptation, allowing improved treatment accuracy in prostate cancer stereotactic body radiotherapy (SBRT). However, fully integrated MRI-Linac systems remain costly and technically complex, limiting their availability. The ARTEMIS (Adaptive Radiation Therapy Enhanced by Magnetic Imaging Systems) Program was developed at the Department of Radiation Oncology at the University Hospital Zurich to implement an integrated MRI-enhanced adaptive treatment technique using a dedicated MRI-simulator combined with CBCT-based delivery systems. This study reports the first dosimetric outcomes of patients with localized prostate cancer treated within the ARTEMIS Program. Material/Methods: From June to October 2025, 21 patients with localized prostate cancer were treated with MRI-enhanced online adaptive SBRT delivered in five fractions. Prior to the first fraction, all patients underwent a planning MRI on a 1.5T Siemens scanner. Contouring was performed on a T2 sequence, followed by base plan calculation using the synthetic CT generated from a DIXON sequence. For each treatment fraction, a simulation MRI acquired immediately before delivery on a 0.55T Siemens scanner was used to generate an adapted plan reoptimized on the daily anatomy. For the analysis, each base plan was recalculated on the anatomy of the day and compared with the adapted plan of the day. Across all 105 fractions, dose-volume parameters were evaluated for target volumes and organs-of-interest, including rectum, bladder, bowel, and urethra.
Figure 1. For organs of interest, maximum doses to the rectum, bladder, bowel, and urethra remained unchanged between recalculated and adapted plans. However, the rectal volume receiving 29 Gy (V29Gy) was significantly reduced following adaptation (p = 0.002), with an absolute reduction of up to 7 cm3 (Figure 2).
Figure 2.
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