Impact of adjuvant fractionated stereotactic radiotherapy dose on local control of brain metastases

Purpose: The aim of this study was to determine whether a higher biological effective dose (BED) would result in improved local control in patients treated with fractionated stereotactic radiotherapy (FSRT) for their resected brain metastases. Methods: Patients with newly diagnosed brain metastases without previous brain radiotherapy were retrospectively reviewed. Patients underwent surgical resection of at least one brain metastasis and were treated with adjuvant FSRT, delivering 25–36 Gy in 5–6 fractions. Outcomes were computed using Kaplan–Meier survival analysis and univariate analysis. Results: Fifty-four patients with 63 post-operative cavities were included. Median follow-up was 16 months (3–60). Median metastasis size at diagnosis was 2.9 cm (0.6–8.1) and median planning target volume was 19.7 cm (6.3–68.1). Two-year local control (LC) was 83%. When stratified by dose, 2 years LC rate was 95.1% in those treated with 30–36 Gy in 5–6 fractions (BED of 48–57.6 Gy) versus 59.1% lesions treated with 25 Gy in 5 fractions (BED of 37.5 Gy) (p < 0.001). LC was not associated with resection cavity size. One year overall survival was 68.7%, and was independent of BED. Symptomatic radiation necrosis occurred in 7.9% of patients and was not associated with dose. Conclusion: In the post-operative setting, high-dose FSRT (BED > 37.5 Gy) were associated with a significantly higher rate of LC compared to lower BED regimens. Overall, 25 Gy in 5 fractions is not an adequate dose to control microscopic disease. If selecting a 5-fraction regimen, 30 Gy in five fractions appears to provide excellent tumor bed control.