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Gamma Knife® Surgery And Microsurgery: A comparison of published results

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”). With the demonstration of the efficacy of Gamma Knife® Surgery considerable interest was evoked to adapt existing tools for radiation delivery for the purpose of radiosurgery. Such research, was prompted primarily by cost considerations and led to the usage of a modified linear accelerator to perform radiosurgery, despite the recognized difficulties. Unlike the natural emission of gamma ray photons produced by Leksell Gamma Knife® cobalt 60 sources, a linear accelerator creates photons by accelerating electrons along a linear path where they collide with a metal target. The resultant single stream of photons must then be made to simulate multiple stationary beams by rotating the patient couch and by controlled movements of the accelerator gantry through multiple non-coplanar arcs around the patient’s head. As with any new technique the developers of radiosurgical techniques and pioneer users were cautious in applying it for different applications, however there now exists a large body of experience that establishes its efficacy and value in the modern management of numerous neurosurgical conditions. The outcomes and consequent cost-savings that can be achieved through radiosurgery have made this technique another tool in the neurosurgical armamentarium used to supplant and or replace conventional microsurgery as indicated in a given case. In this era of cost containment, this approach is of significant interest to third party payers, hospital associations, trade groups, and patient advocacy groups. During the last several years, many comparisons have been made about the relative effectiveness of radiosurgery and microsurgery. Further, additional observations have been made about the relative effectiveness of modified linear accelerators in comparison to Gamma Knife® Surgery. However, organized long term follow up has been lacking. No objective outcomes-based data have been published. Nonetheless, it is extremely valuable to put into perspective the results currently available from the literature; such a synopsis may assist organizations in their evaluation of the role of available treatment modalities. This is the motivation for this compilation of data. This is intended to serve not only as a ready reference for those who wish to quickly review the literature but also as a road map for those intending a deeper study. The diversity of the patient populations that are inherent in comparing two random series make the meta-analysis limited in scope. The caveat for those who see this data is that whereas Gamma Knife® Radiosurgery (GKRS) is a technique that is somewhat operator independent and therefore prone to produce more consistent results microsurgery remains an art that is mastered only with time and patience. The microsurgical results offered for comparison are therefore representing the state of the art and not to be equated with Gamma Knife® Surgery And Microsurgery: A comparison of published results