Stereotactic radiotherapy involves delivery of ionizing radiation to the tumor from multiple directions. A high dose of radiation is therefore focused at the target tissue with relatively little irradiation of surrounding healthy tissues. There are two techniques of delivering stereotactic radiation to the eye: stereotactic radiosurgery and fractionated stereotactic radiotherapy. Stereotactic radiosurgery (SRS) involves multiple radiation beams that are focused onto the tumor simultaneously, from different directions, the treatment usually being completed in a single session or occasionally fractionated over several days. Gamma Knife radiosurgery is delivered using 201 cobalt sources localized in a hemisphere around the patient’s head so that all beams of gamma radiation converge onto the tumor. During fractionated stereotactic radiotherapy (SRT), a single beam of radiation is aimed at the tumor successively from different directions, the entire treatment being delivered either in a single session or, as is usually the case, in a fractionated manner over several sessions.