GammaKnife is a high-precision radiation device with 201 radiation sources which are all accurately aligned to one point. Comparable to a magnifying glass, at this point a therapeutically effective, almost spherical radiation field is emerging. The accuracy of the irradiation is ensured by means of a so-called stereotactic frame with a high-precision coordinate system. This type of radiation concentration makes it possible to irradiate the tumor tissue without damaging any surrounding tissue. This unique treatment method proves particularly useful for the radiosurgical treatment of various brain diseases.