Efficacy of Gamma Knife radiosurgery (GKRS) for patients with metastatic brain tumors (METS) has been mainly evaluated using progression free survival rate or overall survival rate. However, these parameters mainly reflect the patients’ general conditions and do not reflect the local tumor control.

     Here we focused on the local control ratio of each tumor by GKRS in patients with METS from breast cancer.

     Two hundred and fifty four patients were treated by GKRS due to METS from breast cancer.

     The records from 76 consecutive patients who underwent twice or more GKRS for 536 METS were reviewed to examine the local control of each irradiated tumor. It was defined as failed GKRS (recurrence), if the tumor needs to be re-treated at the next GKRS session.

     Mean age at the first GKRS was 52 years. The number of METS in each patient was 1-24 (average 5). The mean KPS was 80.4. Extra cranial metastases were present in 50% of cases. Fifty % recurrence free probability was 26.9 months. Recurrence was observed in 44 tumors (8.8%). Univariate analysis revealed that factors related to favorable tumor control were, 1) tumor volume 1.8mL (equivalent to approximately 1.5cm in diameter) or smaller, KPS less than 70, age 60 or more, 2nd or 3rd GKRS, and 4 or more tumors to be treated at the same time. At the 2nd or 3rd GKRS, tumor volume was significantly smaller compared with tumor volume at the 1st GKRS. Tumor volume was also significantly smaller if the total number of tumor in the patient was 4 or more. Multivariate analysis revealed that the volume 1.8mL or smaller was the only factor which related to a favorable local tumor control.

     This was a retrospective study.

     Tumor volume was the only factor which affects the favorable tumor control by GKRS in METS from breast cancer.

     It is reasonable to treat multiple metastases with GKRS as far as the volume of each tumor is small enough and the integrated dosage delivered onto whole brain is acceptable.