Background. Brain metastases (BM) are the most common intracranial tumor and occur in 20-40% of all oncological patients. The most common primary cancer in brain metastases is lung cancer, followed by melanoma, breast cancer, renal cancer and colorectal cancer. The incidence of brain metastases has been increasing but the occurrence of brain metastases is still associated with high morbidity and poor prognosis. The main treatment methods are stereotactic radiosurgery (SRS), microsurgical resection and whole brain irradiation (WBRT). In contrast to microsurgical resection, Gamma Knife radiosurgery (GKRS) is a non-invasive neurosurgical method, which allows treatment in multimorbid patients with contraindications for surgery in general anesthesia. Furthermore, stereotactic radiosurgery is the only local treatment method for multiple disseminated and thereby non-resectable brain metastases. In general, microsurgical resection is considered the treatment of choice for BM exceeding >3 cm in diameter. However, since the establishment of the dose-staged technique, larger metastases can also be treated radiosurgically in selected patients. This novel method allows the application of high cumulative dose for the treatment of complex brain metastases.

Aim. The aim of the study is to evaluate the clinical outcome in brain metastases patients with tumor volume between 8 and 20 ccm3. The clinical outcome will be compared between surgically and radiosurgically treated BM patients.

Patients and methods. The investigators plan to conduct an explorative prospective study including about 50 radiosurgically and 50 surgically treated patients with brain metastases. If a patient fulfill study-relevant inclusion criteria at the time of BM diagnosis, the principle study investigator will offer both treatment options to the patient. Depending on patient's choice, he/she will be categorized either to surgical or to radiosurgical treatment group. For the outcome evaluation of the different treatment options, a comprehensive database will be established. The study participations will not interfere with any clincally indicated therapeutic decisions and the study participants will not be exposed to any additional risks since both treatments represent suitable therapy options.

Inclusion Criteria:

• Patients over 18 years and under 90 years
• Patients with KPS ≥70
• Patients with NSCLC, melanoma, breast cancer or renal cancer as primary tumor
• Maximum of three brain metastases on the diagnostic MRI
• Tumor volume of 8-20 ccm3 on the diagnostic MRI
• Lobular brain metastases
• Patients without any contraindications for both treatment options
• Written, signed informed consent for study particaption after study explanation

Exclusion Criteria:

• Patients under 18 years and over 90 years
• Patients with KPS <70
• Patients with other primary tumor
• More than three brain metastases on the diagnostic MRI
• Tumor volume <8 or >20 ccm3 on the diagnostic MRI
• Patients with contraindications for both treatment options