ESTRO 2025 - Abstract Book

S647

Clinical - CNS

ESTRO 2025

treatment decisions. This retrospective, single-institutional study evaluated treatment outcomes in a heterogeneous patient population treated with Linac-based SRT, aiming at identifying potential prognostic factors.

Material/Methods: Patients receiving either 1 or 3 fractions of single-isocenter 6FFF VMAT SRT were retrospectively analyzed. The GTV to-PTV margin was 1–2 mm. Treatment plans ensured 99% PTV coverage with 80–90% of the prescribed dose and a 110–115% dose gradient within the GTV, except in cases of overlap with critical organs at risk. Delivered dose was estimated by recalculating plans on roto-translated CT images based on post-treatment CBCT data [1]. Local progression-free survival (LPFS), intracranial progression-free survival (IPFS), and overall survival (OS) were estimated using the Kaplan-Meier method. Inter-group differences were evaluated with log-rank and Wilcoxon Mann-Whitney tests. Univariate and multivariate Cox regression analyses were used to assess prognostic factors. Results: A total of 100 patients (50 females, 50 males; median age 69 years) underwent 107 SRT treatments. In total, 213 BM (range, 1–10 per treatment), with a median volume of 0.22 cc, were treated with a median biologically effective dose (BED) of 59.5 Gy. The median delivered GTV D95 reduction was -0.3%. The median follow-up was 11 months. Nineteen LP events were recorded, with a 1-year local control (LC) rate of 90.1%. GTV coverage was not associated with LC, but GTV volume emerged as a significant risk factor for LP (HR 1.76, 95% CI 1.01–3.03, P=0.044), with a 1 year LC rate of 73% for lesions ≥0.88 cc. There were 17 LP events in at least one metastasis and 52 intracranial progression (IP) events. Median LPFS, IPFS, and OS were 6, 5, and 7 months, respectively. Multiple BM correlated with inferior 1-year IPFS (31.5% vs. 52.1%; P=0.031), and polymetastatic progression was associated with worse 1 year OS (37.9% vs. 54.5%; P=0.006). Multivariate analysis identified melanoma histology and second-line systemic therapy as negative prognostic factors, while adenocarcinoma histology and mutations were associated with better outcomes. Conclusion: This study confirms the accuracy and efficacy of Linac-based SRT for BM, but highlights that dose distribution alone does not predict treatment outcomes. Tumor volume, histology, and systemic treatment history are crucial factors that must be considered to optimize SRT results.

Keywords: linac-based, brain metastases, prognostic factors

References: [1] Faccenda V, Panizza D, Pisoni V, Trivellato S, Daniotti MC, Bianchi SP, De Ponti E, Arcangeli S. Single-Isocenter Linac-Based Radiosurgery for Brain Metastases with Coplanar Arcs: A Dosimetric and Clinical Analysis. Cancers. 2023 Sep 10;15(18):4496. https://doi.org/10.3390/cancers15184496 

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Digital Poster Clinical Impact of Integrating 3D-TSE Imaging into Stereotactic Radiosurgery for Brain Metastases in the Post-Whole Brain Radiotherapy Setting Eyub Y AKDEMIR 1 , Selin Gurdikyan 1 , Robert H Press 1 , Omer Gal 1 , D Jay Wieczorek 1 , Yongsook C Lee 1 , Ranjini Tolakanahalli 1 , Alonso N Gutierrez 1 , Yazmin Odia 2 , Michael W McDermott 3 , Minesh P Mehta 1 , Rupesh Kotecha 1 1 Radiation oncology, Miami Cancer Institute, Miami, USA. 2 Neuro-Oncology, Miami Cancer Institute, Miami, USA. 3 Neurosurgery, Miami Neuroscience Institute, Miami, USA Purpose/Objective: The integration of advanced 3D-TSE sequences into stereotactic radiosurgery (SRS) treatment planning protocols improves imaging sensitivity, but its usefulness in patients with prior whole brain radiotherapy (WBRT) remains