Gamma knife radiosurgery for brain metastases: A primary therapeutic option

Object. The aim of this retrospective study was to assess the role of gamma knife radiosurgery (GKS) as a primary treatment for brain metastases by evaluating the results in particularly difficult cases such as oncotypes - which are unresponsive to radiation - cystic lesions, and highly critical locations such as the brainstem. Methods. Treatment of 804 patients with 1307 solitary (29%), single (26%), and multiple (45%) brain metastases was evaluated. Treatment planning parameters were as follows: mean tumor volume 4.8 cm3 (range 0.01-21.5 cm3), mean prescription dose 20.6 Gy (range 12-29 Gy), and mean number of isocenters 6.5 (one-19). In unresponsive oncotypes such as melanoma and renal cell carcinoma, the mean target dosages were higher. Cystic metastatic lesions were initially stereotactically evacuated and then GKS was performed. Patients with brainstem metastases were treated with lower doses. Conventional radiotherapy was used in only a minority (14%) of selected cases. The overall median patient survival time was 13.5 months, and the 1-year actuarial local progression-free survival rate was 94%, with a mean palliation index and functional independence index of 53.8 and 52.5 weeks, respectively. The local tumor control rate was 93%, with a mean follow-up period of 14 months. In the overall series, and especially in the unresponsive oncotypes, systemic disease progression was the main limiting factor with regard to patient life expectancy. Conclusions. Gamma knife radiosurgery seems to be the primary treatment option for patients harboring small-to-medium size (≤20-cm3) brain metastases with reasonable life expectancy and no impending intracranial hypertension. Results are better than with those obtained using whole-brain radiotherapy and comparable to the best selected surgery-radiation series, even in oncotypes unresponsive to therapeutic radiation, cystic tumors, and tumors located in the brain stem.