Along with surgery and chemotherapy, radiation therapy is an essential treatment option for metastatic and primary tumors of the central nervous system. Radiation toxicity may be compartmentalized into three subcategories including acute toxicities, early-delayed and late delayed effects. Radiation induced toxicity spans from self-limiting fatigue to more serious delayed side effects of radionecrosis. Stereotactic radiosurgery has recently emerged as a highly focused delivery method of tumoricidal irradiation with promising results compared to whole brain irradiation in many cases. Recognizing and understanding toxicity from cranial irradiation can help guide therapy as ever evolving new technologies develop within this integral component of cancer treatment. Part of the book: Brain and Spinal Tumors