Scientific Background: Brain metastases (BM) represent a significant healthcare problem. It is estimated that 20% to 40% of patients with cancer will develop metastatic cancer to the brain during the course of their illness 1. The most common primary sites are lung, melanoma, renal, breast and colorectal cancer 2. Options for patients with brain metastases had been limited to whole brain radiotherapy (WBRT) or supportive care alone, and systemic chemotherapy was often discontinued. Historically, the best possible supportive care or whole-brain radiotherapy (WBRT) were the standard of care 1 aiming at temporary symptom relief. For WBRT, efficacy in symptom relief but also in prolongation of the median survival time by 3-6 months is well documented. To date, microsurgical approaches and SRS, both proved to be safe and efficient, offer alternative treatment options that potentially meet these concerns 6,7. After proving its efficacy in achieving local tumor control in the treated volume, SRS was used as a stand-alone treatment option in patients with oligometastases (one to four metastases) in the brain. There is a rapidly expanding recent body of literature on outcomes of single-fraction SRS or hypofractionated SRS targeting the resection cavity after surgical resection of BM. Several retrospective series assessed the efficacy and safety of postoperative SRS to the resection cavity 9 aiming at an enhanced local tumor control but also at avoidance of the neurotoxic late effects of WBRT. WBRT followed by SRS of the tumor bed leads to 1-year local control rates of 70-93 %, which is comparable to results after surgery followed by WBRT. Median survival was 12-18 months with a 1-year incidence of new metastases in the brain of 45-60 %.

Trial Objectives: This protocol is primarily aimed at evaluating the safety and toxicity profile of SRS following neurosurgical resection and compares it to that of WBRT as the established standard of care. Secondary, the local effect of radiation therapy in patients with brain metastases will be assessed by measuring time to local and loco-regional recurrence, local and loco-regional PFS and overall survival at 12 months after treatment.

Patients´Selection: Patients with the diagnosis of brain metastases from solid tumors that have undergone neurosurgical resection of one brain metastasis will be evaluated and screened for the protocol. All patients fulfilling the inclusion and exclusion criteria will be informed about the study and included into the study if they declare informed consent. Registration for the study must be performed before the start of RT.

Trial Design: The trial will be performed as a single-center two-armed prospective randomized Phase II study. Patients will be randomized into an experimental arm and a control arm. All patients will receive post-operative contrast-enhanced cranial MRI imaging and imaging will be assessed by a radiologist. All available MRI sequences, including SPACE will be taken into consideration for the definition of treatment target lesions. Patients for whom the post-operative MRI reveals more than 10 suspect intracranial lesions (all sequences taken into account) will not be included in the trial.