S1175
Clinical - Urology
ESTRO 2026
Keywords: renal cancer, MRgRT, stereotactic radiotherapy
up until two years post-RT. Results:
Patients’ characteristics are reported in Table 1. 26/30 (86.7%) of patients completed 2-year study follow-up. ATS was conducted in 79 % of fractions. Median duration of plan adaptation was ATS/ATP 17.9/7.3 min (range 12.4-30.0 min/5.0-11.0 min), with a median beam on time of 5.4 min (4.2-7.0 min). Acute GU- and GI toxicities peaked during week 4, with recorded RTOG grade 1/2 GI-toxicity in 43.3%/10.0% and RTOG grade 1/2 GU-toxicity in 66.7%/22.3% of patients. No grade 3 toxicities were reported. At three months, only one patient still reported CTCAE grade 2 urinary frequency; with only grade 1 side effects present (RTOG GU 10%/GI 10.3%). At two years, no CTCAE grade 2 nor RTOG grade 1 GU-/GI-toxicities were reported. At two years, one patient had experienced lymphonodal relapse and received salvage resection with adjuvant pelvic RT (3.3%).
Digital Poster 1176 MR-guided adaptive primary moderately hypofractionated radiotherapy in prostate cancer patients – a prospective single-center study Evgeny Zharov 1 , Simon Böke 1 , Vlatko Potkrajcic 1,2 , Marcel Nachbar 1,3 , Sarah Kübler 1 , Jessica Boldt 1 , Monica LoRusso 1 , David Baumann 1 , Hathal Haddad 1 , Cihan Gani 1 , Frank Paulsen 1 , Daniela Thorwarth 1,4 ,
Karim-Maximilian Niyazi 1 , Elgin Hoffmann 5 1 Department for Radiation Oncology and
Radiotherapy, Eberhard-Karls Universität, Tübingen, Germany. 2 Department of Radiation Oncology, Medical University Vienna, Vienna, Austria. 3 Section for Biomedical Physics, Department for Radiation Oncology, Eberhard-Karls Universität, Tübingen, Germany. 4 Section for Biomedical Physics, Department for Radiation Oncology, Department for Radiation Oncology, Eberhard-Karls Universität, Tübingen, Germany. 5 Department for Radiation Oncology and Radiotherapy, Eberhard-Karls Universität, Tuebingen, Germany Purpose/Objective: MR-guided radiotherapy (MRgRT) for moderate hypofractionation (MHF) in primary radiotherapy (RT) of localized prostate cancer enables superior imaging of pelvic organs and daily adaptive RT with continuous intrafraction imaging. This could permit the reduction in safety margins and thus treatment-related side- effects without compromising oncologic outcomes. Thus, we report 2-year results of a prospective single- center study analyzing feasibility and oncological and toxicity outcomes of prostate cancer patients receiving
MRgRT-based MHF. Material/Methods:
Thirty prostate cancer patients enrolled in the prospective MRL-01-trial (NCT04172753) received primary MRgRT MHF (60 Gy/20 fractions (ICRU), (1)) between 2020-2024 (1.5 T MR-Linac, Elekta Unity, 7 MV Step-and-Shoot-intensity modulated RT, real-time MR motion monitoring). Planning target volume was clinical target volume (prostate; proximal 1/2cm of seminal vesicles included in intermediate/high risk tumors) with a 6mm expansion (dorsal 0mm). Workflow analysis (adapt-to-shape (ATS) vs. adapt-to- position (ATP), treatment time) was conducted. Baseline genitourinary (GU) and gastrointestinal (GI) function, acute and long-term side effects (RTOG/CTCAE), prostate-specific antigen (PSA), oncologic outcome, as well as patient reported outcomes (PROMs) were recorded at 3-month intervals during the first year and at 6-month intervals
Conclusion: MRgRT-based MHF to the prostate was feasible and well-tolerated, in line with published data (1;2). Treatment-related toxicity was limited to CTCAE and RTOG grade 1 and 2 GU which had resolved at two years post treatment. No grade 3 toxicities were reported. As the importance of MRgRT-based MHF compared to standard CT-guided MHF is yet unclear, online adaptive MRgRT for MHF to the prostate might especially benefit patients exhibiting pronounced inter- and intrafraction organ movement or anatomic variations.
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