Gamma Knife Surgery And Microsurgery:

RADIOSURGERY, a term introduced by the Swedish neurosurgeon Lars Leksell, in 1951, refers to the destruction of a discrete target area in the brain using the precise delivery of a single, high dose of radiation through the intact skull. Subsequently the definition was modified to include in addition to destruction the production of a desired biological effect. Early research efforts determined that cyclotrons (as a source for accelerated heavy charged particles) and linear accelerators (a source for variable energy photons) were then too cumbersome and complicated to perform radiosurgery. As a result, Leksell and biophysicist Dr. Borje Larsson designed the first Leksell Gamma Knife as a dedicated neurosurgical instrument to deliver focused radiation for performing radiosurgery. Leksell Gamma Knife consists of a hemispherical or doughnut shaped array of Cobalt 60 sources that naturally emit gamma ray photons at a predictable and easily quantifiable rate. These photons travel as high energy beams, several of which can be converged (focused) on a relatively small target volume. The 183 - 201 separate beams (depending on the model of the Leksell Gamma Knife used) thus allow for a very precise delivery of radiation to the specified area while minimizing the radiation delivered to normal brain tissue adjacent to the target by distributing the incident radiation over a large volume. When used in conjunction with a stereotactic head frame, the precision of radiation delivery is 0.3 mm (0.01).