Change is the law of life. And those who look only to the past or present are certain to miss the future. JOHN F. KENNEDY Since its introduction five decades ago, stereotactic radio- surgery (SRS) has evolved from an investigational concept into a mainstream neurosurgical procedure for the manage- ment of a wide variety of brain disorders. Contemporary neurosurgeons routinely use radiosurgery either as a defini- tive or adjuvant treatment modality in the fields of neuroon- cology and cerebrovascular and functional neurosurgery. Stereotactic radiosurgery offers the surgical neurooncolo- gist a precise and established treatment that, in combination with fractionated radiotherapy, chemotherapy, and conven- tional surgery, offers additional management options for the treatment of patients with brain tumors. 4,5,12 The role of SRS in the management of vascular malformations is also well established. Furthermore, this modality has had a signifi- cant impact on the treatment of patients with brain metas- tases; 4,26,51 in cases in which SRS is possible, these patients more commonly succumb to their uncontrolled extracranial disease than to their intracranial disease. Recently there has been a spate of reports attempting to clarify or to (re)define the terms “stereotactic radiosurgery” and “stereotactic radiotherapy” (SRT). 1,48,66 It has become increasingly clear that the evolution of radiosurgery and ra- diotherapeutic techniques demands a reevaluation of the definition of radiosurgery by organized neurosurgery. These factors led the American Association of Neurological Sur- geons (AANS) and the Congress of Neurological Surgeons (CNS) to form the Stereotactic Radiosurgery Task Force under the auspices of the AANS/CNS Washington Com- mittee. Members of the Stereotactic Radiosurgery Task Force were directed to review, clarify, and recommend to their parent organizations a contemporary definition of SRS, which would take into account historical, current, and potential applications of SRS. The purpose of this paper is to express the position of the AANS as well as that of the CNS on the definition of SRS. Historical Review “Stereotactic radiosurgery” was defined by the Swedish neurosurgeon Lars Leksell in 1951. 57 At that time, Leksell sought to mimic destructive lesions in the brain produced by mechanically invasive stereotactic surgical procedures for movement and pain disorders by delivering a high dose of photon or proton energy to the intended target in a single session, while steep fall-off dose gradients protected the ad- jacent brain. Early efforts involving stereotactically applied ultrasound, orthovoltage x-ray, and accelerated particles such as protons proved inadequate to create these lesions deep in the brain or were otherwise too cumbersome. To overcome these shortcomings, Leksell, Liden, Larsson, and colleagues developed the Gamma Knife in 1967. This de- vice focuses multiple beams of high-energy gamma rays to a common point directed by frame-based stereotactic guid- ance. 55,58 Contemporaries such as Kjellberg, Winston, Lutz, Loeffler, Fabrikant, and others also developed systems us- ing x-rays or particles to achieve the same ends. 22,26,48,73,79 For decades, stereotactic localization was limited to in- formation derived from atlases, plain radiographs, pneumo- encephalograms, and angiograms. 37,38,42,56,71 Throughout his life, Leksell remained active in advancing the state of the art J. Neurosurg. / Volume 106 / January, 2007 J Neurosurg 106:1–5, 2007 Stereotactic radiosurgery—an organized neurosurgery- sanctioned definition GENE H. BARNETT , M.D., 1 MARK E. LINSKEY , M.D., 2 JOHN R. ADLER, M.D., 3 JEFFREY W. COZZENS, M.D., 4 WILLIAM A. FRIEDMAN, M.D., 5 M. PETER HEILBRUN, M.D., 6 L. DADE LUNSFORD, M.D., 7 MICHAEL SCHULDER, M.D., 8 AND ANDREW E. SLOAN, M.D., 9 THE AMERICAN ASSOCIATION OF NEUROLOGICAL SURGEONS/CONGRESS OF NEUROLOGICAL SURGEONS W ASHINGTON COMMITTEE STEREOTACTIC RADIOSURGERY T ASK FORCE 1 Brain Tumor Institute and Department of Neurological Surgery, Cleveland Clinic, Cleveland, Ohio; 2 Department of Neurological Surgery, University of California Irvine Medical Center, Orange; 3 Department of Neurological Surgery, Stanford University Medical Center, Palo Alto; and 6 Tiburon, California; 4 Department of Neurological Surgery, Evanston Northwestern Healthcare, Evanston, Illinois; 5 Department of Neurosurgery, University of Florida, Gainesville; and 9 Neuro-oncology Program, Moffitt Cancer Center, Tampa, Florida; 7 Department of Neurological Surgery, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania; and 8 Department of Neurological Surgery, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark, New Jersey KEY WORDS • stereotactic radiosurgery • American Association of Neurological Surgeons • Congress of Neurological Surgeons 1