@Charm
From what we have been told, Cyberknife is SBRT and may be used to re-radiate, and like surgery basically eradicate, only small tumors (normally < 3mm).

IMRT on the other hand is conformal to a field which may include a known tumor or suspicious site(s) such as lymph node chains, etc..

In a recent presentation to our H&N support group, RO Parag Sanghvi, M.D., M.S.P.H. (RMG/Cyberknife of San Diego) told us they are giving a full-course of IMRT to patients previously treated a decade or so ago with XRT, but he mentioned there are adverse side-effects.

He also said the decision to use SBRT (Cyberknife) instead of surgery for treating a recurrence is conditional and often depends on where the recurrence tumor is and surgical risks involved.

Many of the newest RT systems are able to give SBRT, or IMRT (Tomo, Novalis, Varian, GammaKnife, ect..).