Radiant energy – Irradiation of objects or material – Ion or electron beam irradiation
Reexamination Certificate
1999-09-02
2001-11-13
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Irradiation of objects or material
Ion or electron beam irradiation
C315S501000, C315S507000
Reexamination Certificate
active
06316776
ABSTRACT:
BACKGROUND OF THE INVENTION
A charged particle beam apparatus, which is disclosed in JP-A-5-40479 (1993), will be explained with reference to FIG.
1
.
In
FIG. 1
, the charged particle beam
82
is directed along a path extending in the direction Z. When sine wave currents, having a phase difference of 90° with respect to each other, are supplied to a scanning electromagnet
80
to produce a magnetic field in the X direction and to a scanning electromagnet
81
to produce a magnetic field in the Y direction, respectively, the charged particle beam is scanned circularly by the magnetic fields generated by the respective electromagnets. When the circularly scanned charged particle beam is projected onto a scatterer
83
, the size of the charged particle beam is broadened, and the dose in the irradiation region is distributed as shown in FIG.
2
. The dose becomes uniform in the region within a range of
2
r
, but the dose in the region outside the range
2
r
decreases more for positions farther from the central position and becomes uneven. Accordingly, the uneven irradiation region was cut by a collimator, and only the irradiation region having a uniform dose was used for irradiating an affected portion.
The patent JP-A-7-275381 discloses a method, by which electromagnets are controlled so that the irradiation region is formed in an arbitrary shape.
SUMMARY OF THE INVENTION
However, in accordance with the prior art, the loss of a part of the charged particle beam is significant, because the uneven irradiation region eliminated by the collimator. Furthermore, in order to obtain a large irradiation geld, the thickness of the scatterer
38
for increasing the size of the beam must be increased, causing a further increase in the loss of charged particle beam energy.
One of the objects of the present invention is to provide a charged particle beam apparatus, wherein the loss of energy in the charged particle beam is decreased, and to a method for operating the same.
The present invention relates to a charged particle beam apparatus of the type used for cancer therapy, diagnosis of affected parts, and other applications.
The feature of the present invention to achieve the above objects is in the steps of broadening the size of the charged particle beam using a scatterer, switching the extraction of and stopping the charged particle beam by an extraction switching means, setting an irradiation position of the charged particle beam using an electromagnet, and changing the irradiation position or the irradiation range by controlling the electromagnet with a controlling apparatus during the stopping of the charged particle beam.
In accordance with the above feature, the uneven irradiation region around an irradiation target can be minimized and the loss of the charged particle beam can be reduced in comparison with a case wherein the charged particle beam is enlarged by the scatterer so as to cover all of the region of the irradiation target, because the controlling apparatus changes the irradiation position or the irradiation range during the time the extraction of the charged particle beam is stopped by the extraction switching means, and then, the irradiation target of the charged particle beam is irradiated per each of the irradiation positions or the irradiation range.
Furthermore, in comparison with a case when where scatterer is not used, the irradiation position is changed only a small number of times, and the control is simple, because the size of the charged particle beam is large.
Another feature of the present invention involves charging the irradiation position on the basis of the size of the enlarged charged particle beam by the controlling apparatus. An even irradiation region having a uniform irradiation dose can be formed by overlapping the charged particle beams, and the irradiation target can be irradiated uniformly with the charged particle beam, because the irradiation close of the charged particle beam, which is enlarged by the scatterer, distributes diametrically in approximately a Gaussian distribution with a center at the irradiation position.
Another feature of the present invention involves the steps of determining a target of the irradiation dose in the irradiation region of the irradiation target by an apparatus for setting the target of the irradiation dose, determining the irradiation dose of the charged particle beam in the respective irradiation regions by an irradiation does measuring apparatus, and switching the extraction and stopping the charged particle beam by an extraction switching means on the basis of the target of the irradiation dose and the observed irradiation dose determined by the irradiation does measuring apparatus.
In accordance with the above feature, the target of the irradiation can be irradiated with an uniform beam density even if the intensity of the beam varies depending on time, because the irradiation can be continued by the extraction switching means until the irradiation dose at the irradiation region reaches the target of the irradiation dose.
When the extraction switching means is a radio frequency supplying apparatus for supplying radio frequency electromagnetic field including frequencies of bettor oscillation of the charged particle beam, which circulates in the charged particle accelerator, to the charged particle beam, the amplitude of the bettor oscillation of the charged particle beam is increased by supplied radio frequency electromagnetic field when the bettor oscillation of the charged particle beam circulating the charged particle accelerator is in a resonance condition, and the charged particle beam is extracted from the charged particle accelerator by exceeding a stability limit of the resonance. At this time, since the charged particle beam is extracted with a constant rate, the irradiation target is irradiated with the charged particle beam with an uniform beam density.
Another feature of the present invention is in changing the energy of the charged particle beam by energy varying means, and the irradiation range of the irradiation target can be changed by varying the energy of the charged particle beam during stopping the irradiation.
Another feature of the present invention is in that the charged particle accelerator is provided with an extraction switching means for switching the extraction and stopping the charged particle beam, a charged particle beam transport system is provided with a transportation switching apparatus for switching the transportation and stopping the charged particle beam, and the irradiation apparatus comprises a scattered for enlarging the charged particle beam, an electromagnet for setting the irradiation position of the charged particle beam, and a controlling apparatus for varying the irradiation position based on the size of the enlarged charged particle beam.
In accordance with the above feature, the charged particle beam is irradiated to the irradiation target with the irradiation apparatus by extracting the charged particle beam which is circulating the charged particle accelerator to the irradiation apparatus by the extracting switching means, and transporting the charged particle beam to the irradiation apparatus by the transportation switching apparatus. The irradiation of the charged particle beam to the irradiation target is slopped by slopping the extraction of the charged particle beam from the charged particle accelerator to the irradiation apparatus by the extraction switching means, or stopping the transportation of the charged particle beam by the transportation switching apparatus. Desirable safety can be ensured, because the switching of the irradiation can be performed by two switching means different from each other. When the extraction switching means, or the transportation switching apparatus terminates the extraction of the beam, the controlling apparatus varies the irradiation position to the next point based on the size of the charged particle beam which is enlarged by the scatterer, and the irradiation is performed with an equal dose at every irradiati
Akiyama Hiroshi
Hiramoto Kazuo
Matsuda Koji
Norimine Tetsuro
Tadokoro Masahiro
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Nguyen Kiet T.
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