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Stereotactic radiotherapy for brain metastases (BM) allows very good local control (LC). However, approximately 20 to 30% of these lesions will recur. The objective of this retrospective study was to evaluate the impact of dosimetric parameters on LC in cerebral stereotactic radiotherapy.

Patients treated with stereotactic radiotherapy for 1–3 BM between January 2015 and December 2018 at two French centers were retrospectively included. A total of 349 patients with 538 lesions were included. The median gross tumor volume (GTV) was 2 cm3 (IQR, 0–7). The median biological effective dose with α/β=10 (BED10) was 60 Gy (IQR, 32–82). The median prescription isodose was 71% (IQR, 70–80). Clinical and dosimetric data were obtained. Correlations with LC were examined using the Cox regression model.

The median follow-up period was 55 months (min-max, 7–85). Median overall survival was 17.8 months (IQR, 15.2–21.9). Of the 539 lesions, there were 95 recurrences and LC at 1 and 2 years was 87.1% (95% CI, 84–90) and 78.1% (95% CI, 73.9–82.4), respectively. Univariate analysis showed that systemic treatment, dose to 2% and 50% of the planning target volume (PTV), BED10 > 50 Gy, and low PTV and GTV volume were significantly correlated with better LC. In the multivariate analysis, GTV volume, prescription isodose, and BED10 were significantly associated with LC.

These results show the importance of a BED10 > 50 Gy associated with a prescription isodose <80% to optimize LC during stereotactic radiotherapy for BM.