Gamma knife radiosurgery for brain metastases: do patients benefit from adjuvant external-beam radiotherapy? An 18-month comparative analysis.

OBJECTIVE: To analyze 18 months of results of gamma knife stereotactic radiosurgery in the treatment of brain metastases and determine factors affecting outcome by examining the effectiveness of additional external-beam radiotherapy (XRT).

MATERIALS AND METHODS: Between January 2000 and September 2001, 61 patients with 103 tumors diagnosed as cerebral metastases were treated with gamma knife. Mean patient age was 57 years (range = 36-81). Lung carcinoma (55.7%) was the most common primary cancer, followed by melanoma (14.8%) and breast carcinoma (11.5%). Mean KPS of the patients was 70 (range = 50-90). Twenty-seven patients had solitary metastases while 34 had multiple tumors. Forty-three patients (59 tumors in total) received only radiosurgery, while 18 patients (44 tumors in total) had prior XRT. Tumor volume ranged from 0.5 to 33 cm(3) (mean = 9.74 cm(3)). Mean marginal dose prescription to the tumor was 15 Gy (range = 11-21 Gy).

RESULTS: Median follow-up was 11 months. Twenty-one patients (34.4%) were alive at last follow-up and 40 (65.6%) had died. Seventeen deaths (42.5%) were reported to be due to progressive brain disease, while 23 deaths (57.5%) were due to uncontrolled primary. Control of the treated lesions was achieved in 45 patients (73.8%) and 84 tumors (81.6%). Mean overall survival of the patients is 8 months (range = 1-19 months). The actuarial 12-month tumor control rate using the Kaplan-Meier method for this series is 68.2 +/- 0.06%. Results of the log-rank test revealed that younger age (<55 years), small tumor volume (<10 cm(3)), and increasing tumor dose (>15 Gy) correlated with improved brain disease-free survival (p < 0.05). Overall survival, local tumor control rate and the freedom from brain disease period (based on the appearance of new brain tumors after radiosurgery) were analyzed separately for the groups receiving radiosurgery alone and those with prior XRT to detect any additional benefit of XRT. No statistically significant difference was found between the two groups for any of the considered outcomes.

CONCLUSION: Gamma knife stereotactic radiosurgery is a safe and effective treatment option for patients with cerebral metastases. It provides survival benefits and improves quality of life by achieving excellent control of the brain disease, irrespective of patients' age or number of brain tumors. The addition of XRT in younger patients with small brain metastases does not improve survival and/or control of the brain disease.