How many metastases can be treated with radiosurgery?

We describe postradiosurgical treatment outcomes of our consecutive series of 1,676 patients (654 females and 1,022 males, mean age 63 years, range 19-92 years) who underwent Gamma Knife radiosurgery (GKRS) for brain metastases, focusing particularly on GKRS for multiple lesions. The most common primary cancer was lung (1,057; 63.1%), followed by alimentary tract (198; 11.8%), breast (180; 10.7%), uro-genital (113; 6.7%) and others (128; 7.6%). Mean and median lesion numbers were 7 and 3, respectively, range 1-85. The overall median survival times were 9.0 months in females and 5.9 in males after GKRS (p < 0.0001). The Kaplan-Meier method was used to assess tumor numbers by group: 1-4, 5-9, 10-14, 15-19, 20-24, 25-29, 30-39 and ≥40. The post-GKRS median survival times were 8.3, 5.3, 6.9, 5.2, 5.6, 3.0, 5.3 and 4.3 months, respectively (p < 0.0001). Also, the Kaplan-Meier method was used to compare 15 pairs of groups based on tumor numbers: 1 vs. ≥2, ≤2 vs. ≥3, ≤3 vs. ≥4, ---, and ≤15 vs. ≥16. In each of the 15 pairs, the median survival times of patients with lower tumor numbers were significantly longer than those of patients with higher tumor numbers (p < 0.0001). Furthermore, 14 other pairs of groups, based on tumor numbers, were also assessed by this method: 1 vs. 2, 2 vs. 3, 3 vs. 4, ---, and 14 vs. 15. Among the 14 pairs, only the 1 vs. 2 pair showed a significant median survival time difference (p = 0.0002); no significant differences were detected for the other 13 pairs. Although tumor number was demonstrated to have a significant impact on the duration of survival, approximately 85% of patients with brain metastasis died of causes other than brain disease progression, regardless of tumor number.