S377
Clinical - CNS
ESTRO 2026
3 mm. Organs-at-risk (OARs) were delineated on the same image set. Weekly MR imaging (T1-Gd and T2/FLAIR) was acquired for online adaptive planning using the adapt-to-shape (ATS) workflow. On non-ATS days, an adapt-to-position (ATP) approach was applied using daily non-contrast T1-weighted MR images. Toxicity was assessed using CTCAE v5.0. Results: Four patients (median age: 70.5 years; range [R]: 40– 74) with WHO grade 4 glioblastoma located in the right parietal lobe were included. Three patients received 60 Gy in 30 fractions with concomitant temozolomide (TMZ), and one received 40.05 Gy in 15 fractions without TMZ. All treatments were completed without delays. Median initial GTV and PTV volumes were 40.7 cc (R: 34.5–75.1) and 237.3 cc (R: 230.1–289.1), respectively. Weekly median GTV changes compared to baseline were:Week 1: +5.1% (R: +28.9% to – 4.0%)Week 2: +13.6% (R: +52.9% to –26.1%)Week 3: +21.6% (R: +53.5% to –18.1%)For the three patients completing six weeks:Week 4: +10.1% (R: +51.6% to – 7.1%)Week 5: +22.3% (R: +6.0% to +38.7%)Week 6: +17.7% (R: +0.6% to +34.8%)All patients experienced grade 2 alopecia. No grade ≥ 3 toxicities were observed. Conclusion: Adaptive MR-Linac-based RT for HGG post-GTR is feasible and well tolerated. Notable tumor bed volume changes during treatment highlight the importance of adaptive strategies to ensure optimal target coverage and OAR sparing. References: Tseng CL, Chen H, Stewart J, Lau AZ, Chan RW, Lawrence LSP, Myrehaug S, Soliman H, Detsky J, Lim- Fat MJ, Lipsman N, Das S, Heyn C, Maralani PJ, Binda S, Perry J, Keller B, Stanisz GJ, Ruschin M, Sahgal A. High grade glioma radiation therapy on a high field 1.5 Tesla MR-Linac - workflow and initial experience with daily adapt-to-position (ATP) MR guidance: A first report. Front Oncol. 2022 Nov 28;12:1060098. doi: 10.3389/fonc.2022.1060098. PMID: 36518316; PMCID: PMC9742425.Marwaha AS, Shepard MJ, Karlovits SM, Herbst J, Wegner RE. Advancements in adaptive MR- guided radiotherapy for high-grade gliomas. J Neurooncol. 2025 Aug;174(1):1-6. doi: 10.1007/s11060- 025-05053-6. Epub 2025 Apr 24. PMID: 40272746. Keywords: high-grade gliomas, adaptive, MRLinac Mini-Oral 3130 Neoadjuvant ultrahypofractionated radiotherapy with simultaneous integrated boost for Glioblastoma. Miriam Torrisi 1 , Andrei Fodor 1 , Raffaella Barzaghi 2 , Filippo Folchini 3 , Laura Giannini 1 , Michele Bailo 2 , Chiara Lucrezia Deantoni 1 , Micol Valle 2 , Silvia Snider 2 ,
POF, given decreasing central failures with increasing dose levels. The distribution of in-field and marginal POF for the PETrecvol with respect to the dose- escalated 7600cGy isodose, together with the concordance between the preRT PETlow and PETrecvol suggest that a TBR lower than what was used for this DERT trial could be included in future dose escalation volumes. References: 1Laack, N.N. et al, 2021. Initial Results of a Phase 2 Trial of 18F-DOPA PET-Guided Dose-Escalated Radiation Therapy for Glioblastoma. IJROBP, 110(5) 1383-1395. 2Lundemann, M. et al, 2017. Patterns of Failure for Patients with Glioblastoma Following FET- PET and MRI-Guided Radiotherapy. Radiother Oncol, 122, 380-386. 3Piroth, M.D. et al, 2016. Relapse patterns after radiochemotherapy of glioblastoma with FET PET-guided boost irradiation and simulation to optimize radiation target volume. Rad Oncol, 11:87. 4Niyazi, M. et al, 2012. FET-PET assessed recurrence pattern after radio-chemotherapy in newly diagnosed patients with glioblastoma is influenced by MGMT methylation status. Rad Oncol, 104, 78-82. Keywords: patterns of failure, dose escalation, PET Digital Poster 3064 Initial experience with adaptive MR-linac radiotherapy for high-grade gliomas: tolerability and volume dynamics Alonso La Rosa 1 , Beatriz Moreno 1 , Laura Zaragoza 1 , Carlos Ferrer 2 , Inmaculada Navarro 1 , Patricia Arroyo 1 , Daniel Camacho 1 , Beatriz Sanchez 1 , Marcos Martínez 2 , Giorgia Yang 2 , Camilo Urrea 1 , Concepción Huertas 2 , Felipe Torres 1 , Marta Rodríguez-Roldán 1 , Beatriz Deben 1 , Ana Castaño 1 , Raúl Matute 1 , Rosa Morera 1 1 Radiation Oncology, Hospital Universitario La Paz, Madrid, Spain. 2 Radiation Physics, Hospital Universitario La Paz, Madrid, Spain Purpose/Objective: To evaluate tumor bed volume changes and treatment tolerability during radiotherapy (RT) following gross total resection (GTR) of high-grade gliomas (HGG), using a 1.5T Unity® MR-Linac system (Elekta AB,
Stockholm, Sweden). Material/Methods:
We retrospectively analyzed all adult patients with histologically confirmed HGG who underwent GTR and were treated with MR-guided RT between May and October 2025. The gross tumor volume (GTV) was defined as the T1-Gd+ enhancing tumor bed. The clinical target volume (CTV) included the GTV plus a 15 mm margin, anatomically constrained and adjusted for T2/FLAIR abnormalities. The planning target volume (PTV) was generated by expanding the CTV by
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