Cyberknife Radiosurgery for Patients With Brain Metastases Diagnosed With Either SPACE or MPRAGE Sequence

For patients with cerebral oligometastases who are in adequate clinical condition stereotactic radiosurgery (SRS) is the treatment of choice, being recommended by international guidelines for the treatment of one to four lesions. Newer findings have shown that for patients with more than four lesions SRS can be considered as a favorable alternative to whole-brain radiotherapy (WBRT), the currently established standard-of-care treatment. With modern techniques highly conformal SRS of multiple lesions has become feasible with comparable clinical effort and minimal toxicity as compared to WBRT. Developments in magnetic resonance imaging (MRI- imaging) have produced highly sensitive contrast-enhanced three-dimensional fast spin echo sequences such as SPACE that facilitate the detection of very small and early-stage lesions in a fashion superior to the established Magnetization Prepared Rapid Gradient Echo (MPRAGE) series. Since it has been established that the response of brain metastases to SRS is better for smaller lesions and that WBRT can come at the price of significant neurotoxicity, the investigators hypothesize that 1) earlier detection of small brain metastases and 2) early and aggressive treatment of those by SRS will result in an overall clinical benefit by delaying the failure of repeated localized therapy and thus preserving quality of life and potentially prolonging overall survival. On the other hand however, overtreatment might be a valid concern with this approach since it has yet to be proved that a clinical benefit can be achieved. The current study aims to stretch the boundaries of the term "cerebral oligometastases" by performing SRS for up to ten cerebral metastases, compared to the established clinical standard of four, given that existing data supports the non-inferiority of this approach and given that modern Cyberknife SRS facilitates the treatment of multiple lesions with minimal treatment-associated toxicity.