Gamma Knife Radiosurgery
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Professor Lars Leksell, a Swedish neurosurgeon, was motivated to find a minimally invasive surgery technique to reduce the high morbidity and mortality associated with neurosurgery in the early 1900s. He pioneered stereotactic neurosurgery in 1949 with the development of a guidance frame secured to the patient's head. Using X-ray images, the location of intracranial targets was pinpointed, and the "stereotactic-frame" used to guide a needle-probe through a hole in the skull to the selected target. In 1951, Leksell replaced the stereotactic needle-probe with a dental X-ray tube, with the intention of delivering the dose of radiation through the intact skull. This first radiosurgery procedure was defined as a "single high dose of radiation stereotactically directed to an intracranial region of interest." However, the early external beam radiation units provided low energy and poor penetration through the skull.

In the 1950's, two Canadian centers were credited with the breakthrough introduction of cobalt radiotherapy. Leksell identified this powerful form of gamma radiation as a possible means to treat intracranial targets. He collaborated with biophysicist Borje Larsson to design a hemispheric array of small radiation sources, specifically designed for radiosurgery treatment of intracranial lesions. This first Gamma Knife was manufactured by a Swedish shipbuilding firm 1968. It contained 179 radioactive cobalt sources. A second unit was installed at the Karolinska hospital in Stockholm, and treated hundreds of patients with malignant brain tumors, acoustic neuroma, meningiomas, AVM, Parkinson's disease, trigeminal neuralgia, pituitary adenomas, craniopharyngioma, and other brain tumors. In 1984 and 1985, two new Gamma Knife prototypes were made, with technical refinements including an increased number of cobalt sources to 201. These were installed and extensively used in Buenos Aries, Argentina and Sheffield, England.

The first commercially developed Gamma Knife, the model U, was produced in 1987. The Leksell Gamma Knife has been further refined and improved over the years, incorporating advances in engineering and radiation physics. In 2000, the Model C unit was introduced, and included the automatic positioning system (APS), which utilizes a computer controlled robotic system and verifies targeting position to within 15 microns, below the resolution of an unaided eye. This allows for more accurate targeting. In 2003, the Winnipeg Regional Health Authority commissioned the installation of Canada's first Gamma Knife, a Model C with APS, at the Health Sciences Centre in Winnipeg.

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