ESTRO 2025 - Abstract Book

S1543

Clinical – Mixed sites & palliation

ESTRO 2025

based on tumor location, disease extent, and clinical guidelines. Two fractionation regimens were involved: 27 Gy in 3 fractions to the metastatic lesion with 24 Gy in 3 fractions to the vertebral segment/segments, or 35 Gy in 5 fractions to the lesion with 20 Gy in 5 fractions to the whole vertebra. Overall survival (OS) and local control (LC) were calculated from the SBRT completion to death and local progression, respectively, using the Kaplan-Meier method. Adverse events, including vertebral fractures and reirradiation rates, were documented. Results: The cohort included patients with prostate (n = 36, 41%), breast (n = 24, 27%), and other (n = 28, 32%) cancers. Most patients had solitary metastases (80%), while the remainder had 2 – 3 lesions. The 3-fraction regimen was used in 61 (69%) patients. During a median follow-up period of 48 months, OS was significantly longer in the 3-fraction group compared to the 5-fraction group, with a median OS of 69 vs. 31 months and 3-year OS of 72% vs. 42% (p < 0.001). This difference reflected a higher proportion of favorable diagnoses (p = 0.055) or non-spine metastases (p = 0.032) in the 3-fraction cohort. LC rates were high across all regimens, with no significant difference between groups (p = 0. 060, Fig.1). At 3 years, LC was 87% in the 3-fraction group and 76% in the 5-fraction group. Patients with prostate cancer had the longest OS (3-years OS of 91%) and achieved a 3-year LC of 82% (Fig. 2). No cases of reirradiation were required, and serious adverse events were minimal, with only three cases of pathological fractures, all in osteoporotic bone.