S16
Track-Topic
ESTRO 2026
metastases (BCLM) within a multicenter registry, aligned with ESTRO/EORTC oligometastatic disease consensus. Material/Methods: Retrospective multicenter registry including 107 patients with histologically confirmed BCLM treated 2016–2025 across five European centers. Inclusion: up to five liver metastases, ECOG 0–2, adequate hepatic function; prior systemic therapy allowed. Intervention: CT-guided HDR brachytherapy; GTV delineation; DVH metrics (D98, D100, D95, D90, Dmean). Single-fraction dose 15–25 Gy. Follow-up at 6 and 12 months with RECIST 1.1 criteria. Outcomes: ORR, rPFS, rLRPFS; toxicity per CTCAE v5.0. Results: At 6 and 12 months, ORR was 72% and 82%, respectively. In a single-lesion subgroup (n=65), D98 predicted rPFS (cut-off 18.3 Gy; sensitivity 81%) and ORR12 (cut-off 18.4 Gy; sensitivity 70%), with modest discrimination (AUC ~0.55). Higher D98 and D100 thresholds correlated with better rPFS and rLRPFS; toxicity was acceptable with no grade 4 events; grade 2–3 events occurred in a minority of patients. Findings suggest that achieving adequate D98 coverage significantly influences local control and progression- free outcomes. Conclusion: CT-guided HDR brachytherapy provides high local control with a favorable safety profile in BCLM when dosimetric coverage (D98) is sufficiently high. D98 thresholds around 18.3–18.4 Gy emerge as robust, though limitations (heterogeneity, modest AUC) warrant prospective validation. Results support integrating precise dosimetry planning into oligometastatic breast cancer management and inform future prospective trials. Keywords: breast cancer, liver metastases, brachytherapy
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