Background and purpose: Three doses were compared for local control of irradiated metastases, freedom from new brain metastases, and survival in patients receiving stereotactic radiosurgery (SRS) alone for one to three newly diagnosed brain metastases.
Patients and methods: In all, 134 patients were assigned to three groups according to the SRS dose given to the margins of the lesions: 13-16 Gy (n = 33), 18 Gy (n = 18), and 20 Gy (n = 83). Additional potential prognostic factors were evaluated: age (≤ 60 vs. > 60 years), gender, Karnofsky Performance Scale score (70-80 vs. 90-100), tumor type (non-small-cell lung cancer vs. melanoma vs. others), number of brain metastases (1 vs. 2-3), lesion size (< 15 vs. ≥ 15 mm), extracranial metastases (no vs. yes), RPA class (1 vs. 2), and interval of cancer diagnosis to SRS (≤ 24 vs. > 24 months).
Results: For 13-16 Gy, 18 Gy, and 20 Gy, the 1-year local control rates were 31, 65, and 79%, respectively (p < 0.001). The SRS dose maintained significance on multivariate analysis (risk ratio: 2.25; 95% confidence interval: 1.56-3.29; p < 0.001). On intergroup comparisons of local control, 20 Gy was superior to 13-16 Gy (p < 0.001) but not to 18 Gy (p = 0.12); 18 Gy showed a strong trend toward better local control when compared with 13-16 Gy (p = 0.059). Freedom from new brain metastases (p = 0.57) and survival (p = 0.15) were not associated with SRS dose in the univariate analysis.
Conclusion: SRS doses of 18 Gy and 20 Gy resulted in better local control than 13-16 Gy. However, 20 Gy and 18 Gy must be compared again in a larger cohort of patients. Freedom from new brain metastases and survival were not associated with SRS dose.