Hi!
This is a good site that goes over the difference between Gamma Knife and Cyberknife. The quick and dirty is: Gamma uses gamma radiation, and a head frame screwed into the skull (not as bad as it sounds, I had it for a vestibular schwamoma). Used for head only. Cyberknife may be used on whole body, and uses regular x-ray. Molded face mask attached to stretcher immobolizes head during treatment. Doesn't immobolize quite like the gamma knife frame, but it works. This web site provides technical information, and an expanded version of what I just said:
http://www.irsa.org/radiosurgery.html
Judi