Automatic steering of a high velocity beam of charged particles

• US 3,955,089 A
• Filed: 10/21/1974
• Issued: 05/04/1976
• Est. Priority Date: 10/21/1974
• Status: Expired due to Term

• Current Assignee: Varian Associates
• Original Assignee: Varian Associates
• Inventors: McIntyre, Raymond D., Wood, Jay D.
• Primary Examiner(s): Dixon, Harold A.
• Application Number:
  US05/516,703
• Time in Patent Office: 561 Days
• Field of Search: 250/405, 250/491, 250/385, 250/399
• US Class Current: 250/399
• CPC Class Codes: A61N 5/1048 Monitoring, verifying, controlling systems and methods
• CPC Class Codes: G01T 1/185 with ionisation chamber arrangements
• CPC Class Codes: G21K 1/08 Deviation, concentration or focusing of the beam by electric or magnetic means electron-optical arrangements in electric discharge tubes H01J29/46; details, e.g. electric or magnetic deviating means for direct voltage accelerators or in accelerators using single pulses H05H5/02; arrangements for injecting particles into orbits H05H7/08; arrangements for ejecting particles from orbits H05H7/10
• CPC Class Codes: H01J 47/02 Ionisation chambers

Abstract

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.

Claims

1. In a radiation generating machine:

means for producing and accelerating a beam of charged particles;

an X-ray target positioned in the path of said beam to generate X-rays for irradiation of a subject;

means for supporting said particle beam producing and accelerating means and for moving said beam producing and accelerating means around a subject to be irradiated and thereby changing the position of said beam producing and accelerating means relative to the direction of a force field of the earth;

means for steering the accelerated beam over a certain predetermined beam path relative to said accelerating means;

secondary emission forming means disposed around the predetermined beam path upstream of the beam relative to said X-ray target for generating a field of ionizing radiation outwardly of the beam when the beam impinges upon said secondary radiation forming means;

ionization chamber detector means disposed around the predetermined beam path for detecting the intensity of the ionizing radiation field generated by said secondary emission forming means, said ionization chamber detector means including chamber means filled with an ionizable medium, and electrode means operatively associated with said chamber means for detecting the ionization current signal flowing within said chamber means as a function of position around said beam due to ionization of the medium fill therein caused by ionizing radiation incident thereon;

means for comparing the detected ionization current signals as a function of position of the beam and for deriving an error signal determinative of the deviation of the beam, if any, from the intended beam path;

said beam steering means being responsive to said error signal for steering the beam along a predetermined beam path; and

sample and hold means for sampling and holding the error signal to which the beam steering means is responsive, whereby upon initiation of the beam after interruption of the beam the beam steering means is responsive to the same error signal upon initiation of the beam as it was at the time the beam was interrupted.