What is a Gamma Knife?

The Gamma Knife is not a knife in the conventional sense, but uses a focused array of intersecting beams of gamma radiation (see the picture to the right) to treat lesions within the brain. The technique was invented by a Swedish neurosurgeon, Professor Lars Leksell and provides an alternative method of treatment for a number of conditions, for which open neurosurgery may be either not practicable or carry a high risk of complications.

Here at the National Centre for Stereotactic Radiosurgery we have the Leksell Gamma Knife ‘Esprit’ , and was the FIRST in the world to be installed.

Within the central body of the Gamma Knife there is an array of 192 separate cobalt sources ,each of which produces a fine beam of gamma radiation. The sources are evenly distributed over the surface of the source core so that each beam is directed at a common focal spot at the centre (see picture to the right).

The resultant intensity of radiation at the focus is extremely high whilst the intensity only a short distance from the focus is very low. This enables a high dose of radiation to be delivered to the abnormal tissues whilst sparing the adjacent healthy brain tissue.

The smallest collimators produce a treatment volume which is approximately 5mm in diameter whilst the largest would produce a diameter of approximately18mm. 

Almost invariably a single ellipsoidal focus of radiation fails to match the shape of the abnormal tissues to be treated. By overlapping multiple focii of radiation of varying sizes, the shape of any abnormality can be exactly matched ensuring a precise conformal radiosurgery treatment plan.

Sensitive structures such as the brain stem or optic chiasm can also be avoided, thus ensuring minimal damage to any normal tissue in the brain.

The efficacy of Gamma Knife radiosurgery relies heavily on the inherent precision of the treatment machine and also on the procedures used to identify the position of the abnormal tissues within the brain.

Stereotactic techniques, using a rigid frame fixed firmly to the outer table of the skull, allow the position of any point within the brain to be determined with a very high degree of accuracy

and facilitate the positioning of the patient within the treatment machine with equal accuracy.

The National Centre for Stereotactic Radiosurgery was initially set up by Mr David Forster and is currently led by Mr Julian Cahill.

In 1985 when the Gamma Knife was installed it was one of only three units in the world, the others were in Stockholm, Sweden and Buenos Aries, Argentina.

World wide there are now over 300 Gamma Knife sites , with around 60,000 patients being treated every year..