Stereotactic radiosurgery for brain metastases

Brain metastases are the most common intracranial malignancies in adults, and, depending on primary tumor type, they may affect up to 50 % of cancer patients. Although advances in systemic and local therapies have led to improvements in patient overall survival and progression free survival, there remains substantial opportunities to improve patient outcomes. Stereotactic radiosurgery (SRS) delivers high doses of ionizing radiation with sub-millimeter accuracy to discrete intracranial tumors. It has emerged as the standard of care for patients with limited number of brain metastases, and it serves as a valuable adjuvant after resection. Moreover, SRS is typically seamlessly integrated into systemic therapy treatment regimens. Continued improvement in SRS technology and growing evidence have led to expansion of SRS indications and introduction of new SRS techniques. Frameless SRS technologies have allowed for treatment of larger lesions and even lesions adjacent to critical structures for which single session SRS would not be prudent. Neoadjuvant SRS has recently been proposed as an alternative to adjuvant SRS and appears to help reduce the risk of leptomeningeal dissemination. These novel SRS techniques require further evaluation through prospective clinical trials and registry based studies. In addition, the concurrent combination of systemic therapies with central nervous system (CNS) activity and SRS has yielded promising results with respect to local control and adverse radiation events rates. The concurrent delivery of SRS, precision medicine, and/or immunotherapy requires further refinements to fully optimize patient outcomes. In this review, we detail the current literature on established and forthcoming indications of SRS for brain metastases.