ESTRO 2025 - Abstract Book

S1481

Clinical – Mixed sites & palliation

ESTRO 2025

1121

Poster Discussion Clinical Outcomes of Patients with Multiple Liver Metastases Treated with MR-Guided Stereotactic Radiotherapy Ceren Atahan, Neris Dincer, Gamze Ugurluer, Enis Ozyar, Banu Atalar Radiation Oncology, Acıbadem MAA University, School of Medicine, Istanbul, Turkey Purpose/Objective: Nearly half of cancer patients develop liver metastases during their disease. 1 Advances in systemic therapies have extended survival, increasing the prevalence of multiple liver metastases and need for effective local treatments. MR-Guided stereotactic radiotherapy (MRgSRT) offers superior imaging, adaptive planning, and tumor tracking as a non-invasive local ablative therapy. We evaluated clinical outcomes of patients with multiple liver metastases treated with MRgSRT. Material/Methods: A total of 150 patients with 258 liver metastases were treated with MRgSRT between October 2018 and October 2024 at our department. Forty- two (28%) patients treated for ≥2 metastases were retrospectively analyzed. Treatments were delivered either in single or multiple courses. Oligometastatic states were classified using ESTRO EORTC recommendations. 2 Tumor response was assessed using RECIST 1.1 or PERCIST 1.0. LC was defined as any response other than progression. Toxicity was graded using CTCAE v5.0, and outcomes were analyzed with Kaplan Meier. Results: Forty-two patients with 150 liver metastases were included. Median age was 62.5 years (range 34-88). Colorectal cancer (45.2%) was the most common primary. Before MRgSRT, 33.3% of patients had received liver-directed therapies and 88.8% had systemic therapy. A single treatment course was performed in 57.1% of patients, while 28.6% underwent 2, 11.9% underwent 3, and 2.4% underwent 5 different sequential MRgSRT courses. Most frequent oligometastatic group was repeat progress (42.7%), followed by induced and repeat persistence (13.3% and 12.7%), metachronous progress (12.0%), induced progress (8.7%), metachronous recurrence (7.3%), and repeat recurrence (3.3%). Median treated metastases number per patient was 3 (range 2-12). Metastases were most frequent in segment 4 (27.3%). Median metastasis diameter was 19 mm (range 6-98), and median volume was 2.8 ml (range 0.2- 211). Median total treated volume per patient was 19.9 ml (range 1.2 – 212.5). Median SBRT dose was 45 Gy (range 20-60) in 3 fractions (range 1-8), with median BED10 of 100 Gy (range 48-151.2). Median follow-up was 20.2 months (range 0.7 – 40.9). Median OS was 29.5 months, and one-year LC was 80%. Tumor responses were CR (33.3%), PR (11.3%), SD (10%), and PD (20%). Metachronous recurrence associated with longer survival (p=0.007) and LC was better for ≤3 metastases per patient (p<0.001) compared to ≥4. Acute Grade I -II toxicity occurred in 20%; no Grade ≥3, late, or radiation -related liver toxicities were observed. Conclusion: MRgSRT is effective for patients with multiple liver metastases, achieving high LC and OS with minimal toxicity. Given better prognosis, more aggressive strategies should be considered for ≤3 lesions and metachronous recurrence.

Keywords: MRgSRT, multiple liver metastases, oligometastasis

References: 1 Tsilimigras, D.I., Brodt, P., Clavien, PA. et al . Liver metastases. Nat Rev Dis Primers. 2021 Apr 15;7(1):27. doi: 10.1038/s41572-021-00261-6. PMID: 33859205. 2 Guckenberger M, Lievens Y, Bouma AB, et al . Characterisation and classification of oligometastatic disease: a European Society for Radiotherapy and Oncology and European Organisation for Research and Treatment of