This is a method of operating on tumors in the body, especially the brain, that are either difficult or impossible to operate on using traditional surgical methods. The technology is also referred to as a gamma knife or cyberknife.

Recent developments in imaging technology such as positron emission tomography (PET) and computerized robotic control of the beams of radiation (called computer-mediated stereotaxic radiosurgery) enable surgeons to better concentrate radiation on a single site within the body. The radiation gun is on the end of an arm which is rotated about the target point within patient so that the other parts of the body do not get a toxic dose of radiation. if you drew an imaginary line that represented the radiation beam, it would eventually trace a pattern shaped like a pincusion, with the nexus of lines crossing at the site of the tumor. That way, the tumor gets a killing dose of radiation while the rest of the body receives a relatively mild dosage.