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Stereotactic body radiotherapy (SBRT) for colorectal liver metastasis: Clinical outcomes from the international multi-institutional RSSearch Patient Registry.

e15040 Background: We investigated factors associated with clinical outcome for liver metastases from colorectal primary tumors treated with Stereotactic Body Radiotherapy (SBRT) from a multi-center, international, prospective patient registry. Methods: A subgroup of patients with colorectal liver metastases treated with SBRT was identified from the RSSearch Patient Registry. Patient, tumor and treatment characteristics associated with outcome were evaluated. Dose fractionations were normalized to BED10. Overall survival (OS) and local control (LC) were evaluated using Kaplan Meier analysis and log-rank test. Results: 217 patients with 233 liver metastases from primary colorectal cancer treated with SBRT between 2005-2017 and enrolled in the RSSearch Patient Registry were included. The median follow-up was 15 months (1–75 months). 77% of patients received prior or concurrent chemotherapy. Median tumor volume was 21.95 cm3 (0.5 – 638 cc), median SBRT dose was 45 Gy (16 – 60 Gy) delivered in a median of 3 fractions (1-5). Median number of liver metastases was 1 (1-8). Median overall survival (OS) was 27 months; median local control (LC) was 41 months. One and two-year OS was 75% and 55%, respectively. One and two-year LC was 75% and 66%, respectively. Higher BED10 was associated with improved LC with median LC of 44 months for BED10 ≥ 100 Gy vs 39 months for BED10 < 100 Gy (p = 0.0007). Higher BED10 was also associated with improved OS: median of 33 months for BED10 ≥ 100 Gy vs to 18 months for BED10 < 100 Gy (p = 0.0009). Smaller tumor volume was associated with improved OS: median OS of tumor volume was 34 months for tumors < 20 cc vs 20 months for tumors ≥ 22cc (p = 0.0037). Local control was not significantly associated with tumor volume: median LC for tumor < 22 cc vs ≥ 22cc was 44 months vs 39 months, respectively (p = 0.193). Age, prior or current chemotherapy and BMI were not associated with OS or LC. Conclusions: In this multi-institutional prospective cohort, OS and LC were favorably correlated with small tumor volume and higher BED10.