Clinical StudyFactors influencing local tumor control after Gamma Knife radiosurgery for intracranial metastases from breast cancer

- Metastases (METs) from breast cancer with HER2-positive tumors are good candidates for Gamma Knife radiosurgery (GKRS).
- Five or more lesions are good candidates for GKRS.
- METs of volume ⩽1.2 cm3 are good candidates for GKRS.
- GK model C and Perfexion achieve better local tumor control than does GK model B.
- The recommended dosage is ⩾18 Gy.

Because evaluation of Gamma Knife radiosurgery (GKRS) for brain metastases (METs) has mainly been based on overall or progression-free survival rates, that is, patients' general condition and control of the primary disease, we focused on factors influencing local tumor control after GKRS for METs from breast cancer. Data were retrospectively collected from our institution's records of patients who had undergone GKRS twice or more for METs from breast cancer. Failed GKRS was defined as a tumor needing re-treatment by further GKRS or having already been treated by other modalities prior to later GKRS procedures. Influences of various factors on local tumor control were examined. GKRS was performed on 623 tumors in 123 sessions in 90 patients. Median follow up was 9 months (range 1-41 months). According to multivariate analysis, use of HER2-targeting agents, (hazard ratio [HR] 0.42, 95% confidence interval [CI] 0.18-0.99, p = 0.049), five or more lesions (HR 0.24, 95% CI 0.11-0.51, p < 0.001), volume >1.2 cm3 (HR 3.12, 95% CI 1.62-6.02, p < 0.001), use of GK model B (HR 2.53, 95% CI 1.28-4.98, p = 0.0076), and prescribed dosage ⩾18 Gy (HR 0.19, 95% CI 0.01-0.51, p < 0.001) were predictors of failed GKRS. Patients with METs from breast cancer with HER2-positive tumors, five or more lesions, and tumors of volume ⩽1.2 cm3 are good candidates for GKRS. GK model C and Perfexion achieve better local tumor control than does GK model B. The recommended dosage is ⩾18 Gy.