Radiosurgery refers to the use of multiple radiation beams that converge in one area, allowing that area to receive a large dose of radiation while the surrounding areas receive a minimal dose.
Traditionally radiosurgery was used mainly for intracranial targets, using frame based devices.
Cyberknife is a frameless radiosurgical modality that allows to target also extracranial targets like spine tumors as well as "moving" targets like lung tumors. The cyberknife uses a robot held linac.
The following shows how the Cyberknife works: