S389
Clinical - CNS
ESTRO 2026
University of Bern, Bern, Switzerland. 5 Institute of Diagnostic and Interventional Neuroradiology, Cantonal Hospital Aarau, Aarau, Switzerland Purpose/Objective: Accurate MRI-based detection of brain metastases (BM) is essential for planning stereotactic radiosurgery (SRS). Although spin-echo (SE) sequences such as T1- SPACE have shown superior lesion detectability compared with gradient-recalled echo (GRE)–based T1- MPRAGE, direct dosimetric comparisons and evaluations of clinical impact are lacking. This study aimed to quantitatively and qualitatively compare T1- SPACE and T1-MPRAGE sequences for SRS planning, focusing on lesion detectability, target volume delineation, dosimetric effects, and oncological outcomes. Material/Methods: Quantitative, qualitative, and dosimetric analyses were performed in 51 patients who underwent MRI with T1- SPACE and T1-MPRAGE sequences prior to SRS (SPACE group). An experienced neuroradiologist identified BM on both sequences as the reference standard. For outcome evaluation, distant brain metastasis-free survival (DBMFS) and overall survival (OS) were compared between the SPACE group and a matched control group (n = 51) planned exclusively on the T1- MPRAGE sequence. Results: Compared with T1-MPRAGE, less experienced readers identified more BM on T1-SPACE. T1-SPACE also demonstrated significantly higher contrast and contrast-to-noise ratios (p < 0.001). Dosimetrically, T1- SPACE–based plans showed smaller planning target volumes (p=0.008) and modest but significant reductions in irradiated brain volumes (V12Gy and V10Gy, both p<0.05). Patients planned with T1-SPACE had longer DBMFS (10.4 vs 5.2 months, p=0.024, see Figure) and better OS (p=0.049) compared with the control group.
detectability, more accurate target delineation, and favorable dosimetric and clinical outcomes in patients with BM. These findings support the implementation of T1-SPACE together with T1-MPRAGE as standard imaging marker sequence for SRS planning in patients with BM. Keywords: Brain metastases, Stereotactic radiosurgery
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Reduced Planning Margins in WHO Grade III Gliomas: Patterns of Failure and Survival from a Single-Center Cohort Jerome Nouvel 1 , Clemens Aden 1,2 , Nanna Wielenberg 1 , Angelika Bilger-Zähringer 1 , Anca-Ligia Grosu 1 , Ilinca Popp 1 1 1. Department of Radiation Oncology, Medical Center, Faculty of Medicine, University of Freiburg, Freiburg, Germany. 2 2. St. Elisabeth Hospital Meerbusch-Lank, Specialty Clinic for Orthopedics and Rheumatology, Meerbusch-Lank, Germany Purpose/Objective: Background and purpose: The optimal definition of planning margins for WHO grade III gliomas remains unsettled. We evaluated recurrence patterns, survival and toxicity after adjuvant radio(chemo)therapy delivered with intentionally reduced margins to provide practice-oriented evidence for margin de- escalation. Material/Methods: Material and methods: We performed a retrospective single-center cohort study of adults treated at the Medical Center University of Freiburg from 2013 to 2017. The clinical target volume (CTV) was defined as the gross tumor volume (GTV) + 12 mm and the planning target volume (PTV) as CTV + 3 mm. The primary endpoint was the recurrence pattern. Secondary endpoints were overall (OS) and progression-free survival (PFS), as well as the identification of prognostic factors. Survival was analyzed with Kaplan–Meier methods and exploratory Cox regression included IDH1-status, 1p/19q co- deletion and age. Results: Results: A total of 90 patients were included. Median follow-up time was 42 months. Recurrence was local (within the 95%-isodose) in 86% of cases. Marginal and distant failures were seen in 5% and 9%, respectively. Median PFS was 94 months in oligodendrogliomas, 76 months in IDH-mutant astrocytomas and 11.5 months in IDH-wildtype astrocytomas. Median OS was reached only in IDH-wildtype astrocytomas with 23 months. The survival outcomes are comparable to series using guideline-concordant 2-cm margins. Treatment was
Conclusion: The T1-SPACE sequence offers superior lesion
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