Despite its name, the Gamma Knife is not a knife at all. In fact, the whole point of this tool is to avoid making an incision. Instead, the machine surrounds a patient's head and emits 201 beams of gamma radiation from multiple directions. Alone, each beam is harmless. But when they converge at a particular point, their combined strength is sufficient to treat a diseased mass of tissue.
Surgeons can therefore target a specific area of the brain and avoid damaging cells along the way.