SRT and SRS allow high-precision RT delivery to stereotactically defined cranial lesions (benign or malignant). External fixation devices immobilize the skull virtually eliminating movement. This allows delivery of very high doses of radiation to small targets with rapid dose fall-off that spares the rest of the brain. In SRS, only one fraction of RT is delivered. SRT is fractionated treatment. Treatment delivery can be linac-based (X-rays – single fraction or multiple fractions) or via gamma knife (X-rays - single treatment fraction where about 200 cobalt-60 sources in a hemispheric array are focused onto the target). Frameless systems can now virtually match the positional accuracy of external fixation devices and are less invasive.