Gamma knife in fact it is not a real scalpel, the reason why it is called “knife”, but because of the focus of many beams of gamma rays to a point, its main energy distribution in a small local area centered on the focal point, and this small part of the area outside the region only a very small energy of gamma rays.
Irradiation, as if with a magnifying glass in the sunlight can light a match. Therefore the boundary of the irradiated field is very clear and regular, shaped like a knife cut, so that in the treatment of the tumor can be achieved similar to the effect of surgical excision. If the ordinary whole brain radiotherapy is compared to an assault rifle, then the gamma knife is like a sniper rifle, which can destroy the enemy one by one without harming civilians.