Stereotactic radiosurgery (SRS) combines the principles of sterotaxy, or 3_D target localization, with multiple cross-fired beams from a high-energy radiation source to precisely irradiate an abnormal (oftentimes cancerous) lesion within a patient's body. This technique allows maximally aggressive dosing of the target, while normal surrounding tissue receives lower, non-injurious doses of radiation. The ideal objective is the destruction of the targeted area without damaging any normal tissue. Stereotactic radiosurgery differs from conventional radiotherapy in several ways. The efficacy of radiotherapy depends primarily on the greater sensitivity of tumor cells to radiation relative to normal brain tissue. In standard radiotherapy, the spatial accuracy of the treatment is a secondary concern as normal tissues are protected by administering the radiation dose over multiple sessions (fractions) daily for a period of several weeks. Radiosurgery requires much greater targeting accuracy. Stereotactic radiosurgery protects normal tissues by both selectively targeting only the abnormal lesion, and using cross-firing techniques to minimize the exposure of the adjacent normal tissue.