Radiant energy – Irradiation of objects or material – Ion or electron beam irradiation
Reexamination Certificate
1998-08-19
2001-04-17
Anderson, Bruce C. (Department: 2881)
Radiant energy
Irradiation of objects or material
Ion or electron beam irradiation
C250S3960ML, C250S397000, C250S398000
Reexamination Certificate
active
06218675
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a charged particle beam irradiation apparatus for irradiating a target object with a charged particle beam for medical treatment of cancer, bactericide in foods, improvement of plant breeding, non-destructive inspection of machines, and the invention relates especially to a charged particle beam irradiation apparatus which is capable of reducing power consumption.
In using a charged particle beam (hereafter, referred to simply as a beam) of high energy, which is generated by an accelerator, for medical treatment of cancer, etc., there is a method in which the diseased part is scanned with a charged particle beam, and another method in which the diameter of the charged particle beam is enlarged to make its dose distribution uniform and in which the enlarged charged particle beam is then shaped by using a collimator to fit to the shape of the target object, that is, the diseased part.
In the above two irradiation methods, the method of scanning a target with a charged particle beam has been implemented using the following methods: that is, the wobbler method of scanning a target with a charged particle beam, the raster scanning method of scanning a target with a charged particle beam in a zigzag manner, and the pixel scanning method of irradiating a target in a pixel state manner.
In the above scanning methods, two electromagnets are used, and the beam deflecting directions of the first and second electromagnets are set perpendicular to each other. Also, a plane perpendicular to the axial direction of the beam is scanned by the beam deflected by these electromagnets.
FIG. 7
is a schematic diagram of the composition of a conventional charged particle beam irradiation apparatus in which a beam irradiation unit using the wobbler method is installed in a rotation gantry. A charged particle beam emitted from an accelerator (not shown in the figure) is inputted into the rotation gantry and outputted from an irradiation nozzle
40
. The diseased part is circularly scanned with the charged particle beam output from the irradiation nozzle
40
by two scanning electromagnets
100
and
110
. The scanning electromagnet
100
deflects the beam in the X direction, and the scanning electromagnet
110
deflects the beam in the Y direction. By changing the amount of deflection of the beam in each scanning electromagnet with time, circular scanning can be performed.
In the above-mentioned conventional technique, it is necessary to set the gap between magnetic poles of the scanning electromagnet
110
wide enough so that the beam deflected by the scanning electromagnet
100
is prevented from striking the magnetic poles of the scanning electromagnet
110
, since the deflection direction in the scanning electromagnet
100
is parallel to the magnetic poles of the scanning electromagnet
110
. Widening the gap between the magnetic poles causes a problem in that a larger current is required in order to generate a magnetic field having the necessary strength, which increases the power consumption of the irradiation apparatus.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a charged particle beam apparatus capable of reducing the power consumption of a scanning electromagnet by narrowing the gap between magnetic poles of the scanning electromagnet.
The first feature of the present invention to attain the above object is that, in a charged particle beam irradiation apparatus including a plurality of scanning electromagnets for irradiating a target with a charged particle beam emitted from an accelerator, a quadrupole electromagnetic used between two (the first and second ones) of the scanning electromagnets.
By providing a quadrupole electromagnet between two of the scanning electromagnets, it is possible to adjust betatron oscillation in the charged particle beam so that the crossing point of the trajectory of the beam center and the design center trajectory of the charged particle beam irradiation apparatus (the trajectory of the center on the beam axis when the beam is not deflected by any one of the scanning electromagnets, and hereafter, simply described as the design center trajectory) exists within an effective magnetic field range of the second scanning electromagnet. Thus, the interval between the magnetic poles in the second scanning electromagnet can be narrowed, which can reduce the power consumption of the second scanning electromagnet.
The second feature of the present invention to attain the above object is that the above mentioned charged particle beam irradiation apparatus includes a power source for feeding current to the quadrupole electromagnet and a control unit for controlling the current output from the power source, wherein the two scanning electromagnets comprise a first scanning electromagnet, and a second scanning electromagnet provided downstream of the first scanning electrode, the quadrupole electromagnet being sandwiched between the first and second scanning electromagnets, and a control unit which controls the current so that the crossing point of the trajectory of the beam center and the design center trajectory of the beam irradiation apparatus exists within an effective magnetic field range of the second scanning electromagnet.
By controlling the current fed to the quadrupole electromagnet provided between the two scanning electromagnets so that the crossing point of the trajectory of the beam center and the design center trajectory of the beam irradiation apparatus exists within an effective magnetic field range of the second scanning electromagnet, the interval of magnetic poles in the scanning electromagnet can be narrowed, which can reduce the power consumption of the second scanning electromagnet.
The third feature of the present invention to attain the above object is that, in the above mentioned charged particle beam irradiation apparatus, the crossing point of the trajectory of the beam center and the design center trajectory of the beam irradiation apparatus exists within an effective magnetic field range and is adjusted to be positioned at the center of the second scanning electromagnet.
By positioning the crossing point of the trajectory of the beam center and the design center trajectory of the beam irradiation apparatus within the effective magnetic field range at the center of the second scanning electromagnet, the interval between the magnetic poles in the scanning electromagnet can be minimally narrowed, which can largely reduce the power consumption of the second scanning electromagnet.
The fourth feature of the present invention to attain the above object is that the above mentioned charged particle beam irradiation apparatus includes a power source for feeding current to the quadrupole electromagnet and a control unit for controlling the current output from the power source, wherein the two scanning electromagnets comprise a first scanning electromagnet, and a second scanning electromagnet provided downstream of the first scanning electrode, the quadrupole electromagnet being sandwiched between the first and second scanning electromagnets, and a control unit which controls the current so that the difference between phases in betatron oscillation of the charged particle beam in the first and second scanning electromagnets is approximately an integer multiple of 180 deg.
By controlling the current so that the difference between phases in betatron oscillation of the charged particle beam in the first and second scanning electromagnets is approximately an integer multiple of 180 deg., since the crossing point of the trajectory of the beam center and the design center trajectory of the beam irradiation apparatus exists within an effective magnetic field range of the second scanning electromagnet, the interval between the magnetic poles in the scanning electromagnet can be narrowed, which can reduce the power consumption of the second scanning electromagnet.
The fifth feature of the present invention to attain the above object is that, in a charged particle beam irra
Akiyama Hiroshi
Hiramoto Kazuo
Matsuda Koji
Norimine Tetsuro
Anderson Bruce C.
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
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