RT-04 Stereotactic irradiation for 2 - 3 cm brain metastases: A multicenter retrospective cohort study

Purpose: We retrospectively analyzed the treatment outcomes of Stereotactic irradiation (STI) for large size (2–3 cm) brain metastasis. Materials and methods: One hundred and sixty-nine lesions with 156 patients who underwent STI from January 1, 2013 to December 31, 2015 at 21 institutions participating in the Japanese Radiation Oncology Study Group were included in the study. Patients who had a history of whole-brain irradiation in the past and those who received whole-brain irradiation sequentially with STI were excluded. RANO-BM was used to evaluate the effect on each lesion, and the survival time or time to occurrence of local failure was defined as the number of months from the initial day of STI to the day of the events. Results: The median age was 66 (33–87) years. The median follow-up time was 14 (1–52) months. Male/female = 95/61 cases. The number of brain metastases was 1/2/3/4 or more = 93/35/14/14 cases. The median doses and fraction size were 30 Gy in 3 fractions. The primary site was lung/breast/colon or rectum/others = 95/14/14/33 cases. The median survival time was 16 months. A 1-year overall survival rate was 62% and a 1-year local control rate was 77%. Comparing the 1-year local control rate by the fraction size, single/3 or 4 /5 or more = 66/86/75%, the rate was better in the 3–4 fractions group (Log-rank test, p = 0.069). Cerebral necrosis (Grade 1/2/3/unknown = 9/10/8/3 cases) was observed in 30 lesions (18%), and the median time to diagnosis of brain necrosis was 9 (1–41) months. The incidence of necrosis in the single fraction cases was 29%, which was significantly higher than that in the fractionated irradiation cases (15%) (p = 0.039). Conclusion: Fractionated STI seems to be more favorable than single fraction STI for large brain metastases.