Brain metastases, Fractionated stereotactic radiation therapy, Post-operative radiosurgery, Stereotactic radiosurgery (SRS), Time to initiation, Adult, Aged, Aged, 80 and over, Brain Neoplasms, Combined Modality Therapy, Dose Fractionation, Radiation, Humans, Middle Aged, Neurosurgical Procedures, Postoperative Period, Prognosis, Radiosurgery, Time-to-Treatment