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A stereotactic neurosurgery in which the usual rigid needles or probes are replaced with beams of ionizing radiation directed toward an intracranial target so as to achieve local tissue destruction. No skin incision or skull opening is required. It is performed with the "gamma knife", a self-contained unit with 201 cobalt-60 sources or with an isocentric linear accelerator (linac). (Goodman, M.L., Southern Medical Journal, vol. 83, May 1990, pp. 551-4)