Varian Associates, Inc.

Jay D Wood

Raymond Denzil McIntyre

In a high energy X-ray therapy machine, an accelerator accelerates a beam of electrons to energies of several MEV. The electron beam is directed, generally via a beam deflector, onto an X-ray target to produce X-rays for treating a patient. The accelerator and beam deflector are often carried within a rotatable gantry structure, movable for radiating the patient through a series of angular positions or ports. A plurality of ionization chamber radiation detectors are disposed in the radiation field surrounding the beam path of the accelerated electron beam. Ionization current signals are compared from a plurality of the detectors to derive an error signal determinative of a deviation of the beam from an intended beam path. The error signal is utilized to energize beam steering coils for steering the beam along the predetermined beam path. A sample and hold circuit is provided for sampling and holding the error signal to allow interruption of the beam for extended periods of time as may be encountered in the prescribed therapy treatment, while maintaining the proper beam steering conditions.

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Cupertino, CA, United States of America

Jay D Wood