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See also: radiosurgery.
Gamma Knife is a registered trademark of Elekta Radiosurgery of Atlanta, Georgia. The system was developed in the late 1960s by Lars Leksell and Borge Larsson of Sweden. As a preliminary to use of the Gamma Knife, the lesion to be ablated is precisely located by imaging techniques such as MRI, CT, PET, and angiography. Beams of gamma rays from 200 cobalt-60 sources are then directed by a computer so that they converge on the lesion. A series of exposures are made during a period of about 1 hour. Lesions larger than about 3 cm cannot be treated. The mechanism is bulky and costly, but the procedure has shown a success rate of about 85% in the treatment of arteriovenous malformations and 50-95% percent for neoplasms. Besides avoiding the risks and complications of open surgery, the Gamma Knife permits treatment of lesions the location of which prohibits any attempt at surgical removal. In addition, patient discomfort is minimal and most patients remain in the hospital for only 1 night. Many return home, or even to work, on the day of treatment. The Gamma Knife has demonstrated limited usefulness in the treatment of other disorders, such as tumors of the eye and the pituitary gland, trigeminal neuralgia, epilepsy, parkinsonism, and other movement disorders.