JP2001009050A - Radiotherapy device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To take out electron beams of a plurality of orbits without increasing the size of a main electromagnet by providing a port for taking-out the electron beams on the straight orbits of the electron beams which are emitted from the magnetic field area of the second main electromagnet formed to be larger than that of the first main electromagnet. SOLUTION: The electron beams which are made incident to the magnetic field range of the second main electromagnet 107 is deflected by 180 deg., and draws a second circular arcuate orbit 119. The electron beams along the second orbit 119 is deflected by 180 deg. by the first main electromagnet 106 and passes through a circular arcuate orbit to be emitted to a linear accelerator 108 and is accelerated by the linear accelerator 108 again. Mass is increased in the electron beams in this case so that the third orbit 120 being the larger circular arcuate one is drawn when 180 deg. deflection is obtained by the second main electromagnet 107. The electron beams are deflected by a deflection magnet 109, a target is irradiated with them, X-rays are generated, a visual field range is restricted by a collimator 112 and a testee body set on a diagnosing device is irradiated with the electron beams.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiotherapy apparatus, and more particularly to a technique effective when applied to a radiotherapy apparatus using a racetrack type microtron as an electron beam accelerator.

[0002]

2. Description of the Related Art In a conventional radiotherapy apparatus using an electron beam accelerator, an object is irradiated with an electron beam or an X-ray generated by colliding the electron beam with a target. Some electron beams were generated using an electron beam accelerator called a race track type microtron.

A conventional race track type microtron is composed of two main electromagnets, a linear accelerator, and an electron gun. The electron gun had a configuration in which an electron beam was generated and incident on a linear accelerator. A microwave was supplied into the linear accelerator, and an electric field was excited. The electron beam incident on the linac was accelerated by the electric field excited inside and received a predetermined amount of energy. At this time, main electromagnets were arranged at both ends of the linear accelerator, and the orbit of the electron beam reaching the end of the linear accelerator was inverted by 180 degrees by the main electromagnet. As described above, in the radiation therapy apparatus using the conventional race track type microtron, desired energy is given to the electron beam by repeating the acceleration of the electron beam by the linear accelerator.

In order to accelerate an electron beam efficiently, it is necessary that the energy received by the electron beam when passing through a linear accelerator is always the same. On the other hand, the electric field in the linear accelerator was excited by a microwave having a constant frequency, and changed periodically according to the frequency.
In order for the electron beam to be accelerated with the same electric field each time and receive the same energy, the phase of the electric field when the electron beam enters the linear accelerator had to be the same. The speed of the electron beam once accelerated in the linear accelerator has the speed of light,
It is known that the speed will not be exceeded. Therefore, in order to make the electron beam incident when the phase of the electric field is the same every time, the distance until the electron beam returns to the linear accelerator is an integer multiple of (speed of light) × (cycle of microwave). In the conventional race track type microtron, the trajectory of the electron beam is set so as to satisfy this condition.

In order to accelerate electrons efficiently with a racetrack type microtron, it is necessary to make the trajectory of the electron beam the same. That is, it is known that by increasing the energy received by the electron beam in the linear accelerator and increasing the magnetic flux density of the main electromagnet, the electron beam can be accelerated efficiently without changing the trajectory of the electron beam.

The extraction of the electron beam has been performed by an extraction electromagnet provided at a linear portion of each orbit. The take-out electromagnet changed the traveling direction of the electron beam and led it to the outside.

Such a race track type microtron is disclosed in R. Rosander, M, Sedlacek and O. Wernholm, Nucleus.
ar Instruments and Methods, 201,1982, P1-20, THE 50eV
RACETRACK MICROTRON AT THE ROYAL INSTITUTE OF TEC
HNOLOGY STOCKHOLM ".

In the conventional race track type microtron, the one used for the physical experiment is diverted for the treatment, so that the output energy (20 MeV or more) which is not always used for the treatment is necessarily used. There was something.

[0009]

SUMMARY OF THE INVENTION As a result of studying the above prior art, the present inventor has found the following problems.

[0010] With the advance of medical technology in recent years, the therapeutic field to which the radiotherapy apparatus is applied is expanding, and the disease to which the radiotherapy apparatus is applied is also increasing, and the required energy of electron beam or radiation is also increasing. Various things are needed.

However, in the conventional radiotherapy apparatus, it was necessary to increase the number of orbits of the electron beam in order to increase the energy type of the electron beam extracted from the racetrack type microtron. For this reason, in the conventional race track type microtron, it is necessary to use a main electromagnet having a size corresponding to the number of orbits of the electron beam, and there is a problem that the race track type microtron becomes large. For this reason, in the conventional radiation therapy apparatus, it was necessary to guide the electron beam generated by the race track type microtron installed in the stand or the adjacent room to the irradiation head arranged at the tip of the gantry. . As a result, there has been a problem that the entire radiotherapy apparatus becomes large and a space for installation increases.

Further, since it becomes necessary to control the magnetic flux density with high precision in order to control a plurality of orbits accurately,
There has been a problem that the electromagnet and its power supply become expensive, and the entire device becomes expensive.

Further, in setting the current of all electromagnets, it is general to gradually increase the current, hold the current at a certain current value larger than the set value for a predetermined period, and gradually reduce the current. In order to increase the size of the main electromagnet and to provide the magnetic flux density with high precision, it was necessary to spend a longer time than other electromagnets. In this case, the time required to increase and decrease the current supplied to the main electromagnet required about 5 to 10 minutes, and a much longer time was required as compared with about 5 seconds, which is the time required by other magnets. For this reason, when the current of the main electromagnet is changed in the conventional radiotherapy apparatus, there is a problem that the time required for one treatment increases and the diagnosis efficiency decreases.

An object of the present invention is to provide a radiotherapy apparatus in which a race track type microtron is integrated with a gantry.

Another object of the present invention is to provide a radiotherapy apparatus capable of extracting electron beams in a plurality of orbits without increasing the size of the main electromagnet.

Another object of the present invention is to provide a radiotherapy apparatus capable of extracting electron beams in a plurality of orbits without improving the accuracy of the magnetic flux density of the main electromagnet.

Another object of the present invention is to provide a radiotherapy apparatus capable of improving diagnostic efficiency.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0019]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

(1) an electron generating means for generating an electron beam;
A linear accelerating means for accelerating the electron beam in a linear direction, a first main electromagnet and a second main electromagnet opposed to each other via the linear accelerating means, wherein the electrons are the first main electromagnet. And a radiation therapy apparatus including an electron beam accelerator configured to draw an elliptical orbit between the magnetic fields formed by the second main electromagnet and the second main electromagnet. The magnetic field region of the second main electromagnet was formed large, and the electron beam outlet was provided on the linear trajectory of the electron beam emitted from the magnetic field region of the second main electromagnet.

(2) In the radiotherapy apparatus according to the above (1), the electron beam is drawn in the magnetic field generated by the second main electromagnet rather than the trajectory drawn in the magnetic field generated by the first main electromagnet. The locus has been increased.

(3) In the radiotherapy apparatus according to the above (1) or (2), an outlet for the electron beam is provided on the linear orbit in the elliptical orbit.

(4) In the radiotherapy apparatus according to (3), the electron beam is changed by changing the magnetic flux density of a second main electromagnet located farther from the electron beam outlet. Controls whether to accelerate or take out directly in an oval orbit.

(5) In the radiotherapy apparatus according to any one of (1) to (4), the magnetic flux densities of the first and second main electromagnets are variable based on the amount of electron beam acceleration by the linear acceleration means. Control means for performing the operation.

According to the above-mentioned means (1) to (5),
The magnetic field region of the second main electromagnet is formed to be larger than the magnetic field region of the first main electromagnet arranged oppositely, and the electron beam is extracted on the linear trajectory of the electron beam emitted from the magnetic field region of the second main electromagnet. With the provision of the opening, the energy level of the electron beam increases, and the semicircular trajectory drawn by the electron beam in the magnetic field region of the second main electromagnet increases. From the magnetic field region of the second main electromagnet, a linear trajectory is drawn in an elliptical trajectory, which is incident on the electron beam outlet and is extracted.
An extraction electromagnet for extracting an electron beam having a desired energy level from an ellipse and a power supply for the extraction electromagnet, which have been conventionally required, can be dispensed with, and the apparatus configuration can be simplified. As a result, it is possible to reduce the size of the electron beam accelerator of the type in which the electron beam is accelerated along an elliptical trajectory.

Therefore, a radiation therapy apparatus in which a race track type microtron, which is an electron beam accelerator for accelerating an electron beam with an elliptical trajectory which cannot be built in a gantry in the past, is built in the gantry. Can be provided.

At this time, by controlling the magnetic flux density of the second main electromagnet for performing the final acceleration with respect to the electron beam, the trajectory of the electron beam is moved to the trajectory leading to the outlet or again to the first main electromagnet. Therefore, it is possible to select the trajectory leading to the second main electromagnet through the magnetic field region, so that the electron beam can be accelerated to a plurality of energy levels.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings together with embodiments (examples) of the invention.

In all the drawings for describing the embodiments of the present invention, components having the same functions are denoted by the same reference numerals, and their repeated description will be omitted.

FIG. 1 is a view for explaining a schematic configuration of a radiotherapy apparatus according to an embodiment of the present invention, wherein 101 is an electron gun, 102 is a first incident correction electromagnet, and 103 is a second incident correction electromagnet. , 104 is a first displacement electromagnet, 105 is a second displacement electromagnet, 106 is a first main electromagnet, 107 is a second main electromagnet, 108 is a linear accelerator, 109 is a deflection magnet, 110 is a target, and 111 is a target. Dose monitor, 112
Is a collimator, 113 is an electron gun power supply, 114 is a klystron, 115 is a klystron power supply, 116 is a stand, 117 is a gantry, 118 is a first trajectory, 119 is a second trajectory, and 120 is a third trajectory. Also, X,
Y and Z indicate an X axis, a Y axis, and a Z axis, respectively.

In FIG. 1, an electron gun 101 is a well-known electron gun that generates thermoelectrons (hereinafter simply referred to as “electrons”) according to a voltage (current) supplied from an electron gun power supply 113. The emitted electrons are emitted as a parallel electron beam, that is, an electron beam (hereinafter simply referred to as “electron beam”).

The first incident correction electromagnet 102 is an electron gun 1
This is a well-known incident correction electromagnet for correcting the trajectory of the electron beam emitted from the light emitting device 01.

The second incident correction electromagnet 103 is used when an electron beam passes through a trajectory from the linear accelerator 108 to the second main electromagnet 107 via the first incident correction electromagnet 102 and the second incident correction electromagnet 103. , First incident correction electromagnet 10
This is a well-known incident correction electromagnet for returning the trajectory of the electron beam bent by 2 to the original eaves path.

The first displacement electromagnet 104 and the second displacement electromagnet 105 displace the direction of the electron beam emitted from the linear accelerator 108 along the first trajectory 118, and move the electron beam from the first main electromagnet 106. Second displacement electromagnet 105
And a known displacement electromagnet for displacing the direction of the electron beam reaching the linear accelerator 108 via the first displacement electromagnet 104 so as to follow the second trajectory 119.

The first main electromagnet 106 is a well-known main electromagnet that generates a uniform magnetic field. In the present embodiment, the first main electromagnet 106 has a first trajectory 118 and a trajectory corresponding to the energy, that is, the mass of the electron beam. It is large enough to form two tracks 119.

The second main electromagnet 107 is a main electromagnet for changing the trajectory drawn by the incident electron beam. In the present embodiment, the second main electromagnet 107 is generated based on an output value input from an operation panel (not shown). By changing the intensity of the applied magnetic field, a selection is made as to whether the incident electron beam is a trajectory along the second trajectory 119 or a trajectory along the third trajectory 120. In the present embodiment, the magnetic field region of second main electromagnet 107 is formed to be larger than the magnetic field region of first main electromagnet 106. Further, the size of the second main electromagnet 107 itself is larger than that of the first main electromagnet 106.

The linear accelerator 108 is a klystron 114
Is a known linear accelerator that uses a microwave source to accelerate an electron beam incident from the X-axis direction and the direction opposite to the X-axis. In this embodiment, the electron beam is in a range of 3 to 7 MeV in one pass. Can give energy.

The deflecting magnet 109 is a well-known deflecting magnet provided on an irradiation head portion which is a tip portion of the gantry 117, and converts an electron beam taken out along the third orbit 120 and parallel to the X-axis direction into the gantry 117. It is deflected in a direction perpendicular to the rotation center axis.

The target 110 is a well-known target for converting an electron beam accelerated to a predetermined energy amount into an X-ray, and generates an X-ray beam based on the dose of the electron beam irradiated on the target 110. You. However, needless to say, when the target 110 is not used, the electron beam can be directly irradiated.

The dose monitor 111 is a well-known dose monitor for detecting the dose of the X-ray beam generated by the target 110, and the collimator 112 displays the irradiation field of the X-ray beam generated by the target 110. This is a well-known collimator for setting a field of view suitable for the affected part of the subject.

The electron gun power supply 113 is a known power supply for supplying a voltage and a current to the electron gun 101 based on a control output of a control unit (not shown).

The klystron 114 is a linear accelerator 108
Is a well-known klystron for supplying microwave power for accelerating the electron beam to the electron beam, and operates with driving power supplied from a klystron power supply 115.

The stand 116 is a well-known stand that rotatably supports the gantry 117 about a rotation axis indicated by a chain line. The stand 116 is provided with a well-known rotation mechanism (not shown) that rotatably supports the gantry 117. The rotation mechanism rotates the gantry 117 based on a rotation instruction from an operation panel (not shown) to set the irradiation angle of the X-ray beam to a predetermined angle.

However, in the radiation therapy apparatus according to the present embodiment, the electron beam emitted from the electron gun 101 is applied to the linear accelerator 1
Acceleration direction when entering at 08 (direction opposite to X axis)
And the acceleration direction (X-axis direction) when entering the linear accelerator 108 along the first orbit 118 and the second orbit 119
Means that the electron beam must be accelerated in different directions. Therefore, in the radiation therapy apparatus according to the present embodiment, when the electron beam enters the linear accelerator 108 in the same direction as the X-axis direction and when the electron beam enters from the opposite direction, the electron beam The distance of each orbit is set so that the phases are different by 180 degrees.

As shown in FIG. 1, in the radiation therapy apparatus according to the present embodiment, a linear accelerator 108 constituting a race track type microtron is provided in a gantry 117, and
The first and second main electromagnets 1 through the linear accelerator 108
06, 107 are opposed to each other and the third track 12
The deflection magnet 109 is arranged on the extension of 0. A target 110, a dose monitor 111, and a collimator 112 are arranged on a deflected electron beam trajectory in an irradiation head portion where the deflection magnet 109 is arranged. Also, an electron gun power supply 1
13, klystron 114 and klystron power supply 1
15 are disposed in the gantry 117.

Next, the operation of the radiotherapy apparatus according to the present embodiment will be described with reference to FIG.

The trajectory of the electron beam emitted from the electron gun 101 is corrected by a first incident correction electromagnet 102 to a race track trajectory indicated by a thin line in the figure, and the linear accelerator 1
08. The electron beam incident on the linear accelerator 108 is accelerated by the electric field formed by the microwave and is emitted from the emission port. The traveling direction of the electron beam emitted from the linear accelerator 108 is displaced by the first displacement electromagnet 104, the second displacement electromagnet 105, and the first main electromagnet 106, and the electron beam travels along the first trajectory 118 shown in FIG. Take. However, the first trajectory 118 is such that the electron beam emitted from the linear accelerator 108 passes through the second displacement electromagnet 104 and the first main electromagnet from the first displacement electromagnet 104 and then returns to the second displacement electromagnet 105 and the second This is a trajectory returning to one displacement electromagnet 104.

The linear accelerator 108 passes through the first orbit 118
The electron beam re-incident on the linear accelerator 1
08 in the X-axis direction. Here, the electron beam reaching the first incident correction electromagnet 102 is deflected by the magnetic field, but the electron beam accelerated twice by the linear accelerator 108 has a mass due to the relativistic effect. Since it is large, the degree of deflection is small. The second incident correction electromagnet 103 corrects the influence of the deflection by the first incident correction electromagnet 102 by returning the electron beam deflected by the first incident correction electromagnet 102 to the original orbit.

The electron beam reaching the second main electromagnet 107 is
The trajectory follows the preset X-ray beam output or electron beam output. For example, when the maximum output is set, the electron beam is applied to the second main electromagnet 107 by the second trajectory. As shown in FIG. 119, a large current is supplied and the magnetic field strength is large. Therefore,
The number of electron beams incident on the magnetic field range of the second main electromagnet 107 is 1
After being deflected by 80 degrees, an arc-shaped second trajectory 119 is drawn. The electron beam along the second orbit 119 is deflected by 180 degrees by the first main electromagnet 106, passes through an arc-shaped orbit that enters the linear accelerator 108, and is accelerated again by the linear accelerator 108. . Since the electron beam at this time has further increased its mass, when it is again deflected by 180 degrees by the second main electromagnet 107, it draws the third orbit 120 which is a larger arc-shaped orbit. It will be. The electron beam describing the third orbit 120 is
The target 110 is deflected by the deflecting magnet 109, and an X-ray beam is generated. The field of view of the X-ray beam is limited by the collimator 112, and the X-ray beam is irradiated on a subject (not shown) set on a diagnostic device (not shown).

FIG. 2 is a view for explaining a schematic configuration of the race track type microtron of this embodiment.
01 is a vacuum vessel, 202 is an electron beam outlet, 203 is a power supply for the first incident correction electromagnet, 204 is a power supply for the second incident correction electromagnet, 205 is a power supply for the first displacement electromagnet, 20
Reference numeral 6 denotes a second displacement electromagnet power source, 207 denotes a first main electromagnet power source, 208 denotes a second main electromagnet power source, 209 denotes a microwave oscillator, 210 denotes an accelerator control device, and 211 denotes an operation panel. However, the race track type microtron of the present embodiment has the electron gun 101 inside the vacuum vessel 201.
And the linear accelerator 108 are arranged. By sandwiching the vacuum container from above and below (in the Z-axis direction in FIG. 2),
The first and second main electromagnets 106 and 107, the first and second displacement electromagnets 104 and 105, and the first and second incident correction electromagnets 102 and 103 are arranged.

In FIG. 2, an electron beam outlet 202 is an outlet for an electron beam from the main body of the race track type microtron. In the present embodiment, a trajectory (third path) leading to the electron beam outlet 202 is used. Orbit 120)
Control the electron beam to draw.

The first incident correction electromagnet power supply 203 and the second incident correction electromagnet power supply 204 correspond to the first incident correction electromagnet 102 and the second incident correction electromagnet 1, respectively.
This is a known electromagnet power supply for supplying a drive current to the motor 03, and supplies a current based on a control output from the accelerator control device 210.

A first displacement electromagnet power supply 205 and a second displacement electromagnet power supply 206 are well-known electromagnets for supplying a drive current to the corresponding first displacement electromagnet 104 and second displacement electromagnet 105, respectively. A power source that supplies a current based on a control output from the accelerator control device 210.

The first main electromagnet power supply 207 and the second main electromagnet power supply 208 are well-known electromagnets for supplying drive current to the corresponding first main electromagnet 106 and second main electromagnet 107, respectively. Power supply, accelerator control device 2
A current is supplied based on the control output from.

The microwave oscillator 209 is a known microwave oscillator for supplying a microwave to the klystron 114. The klystron 114 amplifies the microwave supplied from the microwave oscillator 209 and supplies the microwave power to the linear accelerator 108. Supply.

The accelerator control unit 210 controls the electron gun power supply 113 based on the irradiation conditions input from the operation panel 211.
Controls the klystron power supply 115, the first and second power supplies for incident correction electromagnets 203 and 204, the first and second power supplies for displacement electromagnets 205 and 206, and the first and second power supplies for main electromagnets 207 and 208. Control means.

In order to accelerate the electron beam efficiently with this race track type microtron, it is necessary that the energy received when the electron beam passes through the linear accelerator 108 is always the same. On the other hand, the electric field in the linear accelerator 108 is excited by a microwave having a certain frequency, and changes periodically at that frequency. Therefore, in the race track type microtron of the present embodiment, in order to satisfy this condition, the electron beam is accelerated by the same electric field every time,
In order to receive the same energy, the phase of the electric field when the electron beam enters the linear accelerator 108 is set as shown below.

When the electron (electron beam) accelerated by the linear accelerator 108 enters the linear accelerator 108 for the second time, the electron (electron beam) is accelerated in a direction opposite to that in the first acceleration. The path length is determined so as to deviate by degrees. At the third incidence, the beam is accelerated in the same direction as the second incidence. Therefore, the path length is determined so as to have the same phase as that at the second incidence.

As described above, in the present embodiment, as a condition for efficiently accelerating the electron beam, the trajectory of the electron beam is kept in the same shape, that is, the energy received by the electron beam in the linear accelerator 108 is increased. In this case, the trajectory of the electron beam is kept constant by increasing the magnetic flux density of each electromagnet.

As the specific value, for example, when the energy received by the linear accelerator 108 is 5 MeV, the magnetic flux density becomes about 1 T, and when the received energy is 3 MeV, it becomes 3 T / 5.

Next, a condition for efficiently accelerating the electron beam, that is, a procedure in which the accelerator controller 210 determines a set value for each power supply will be described.

Based on the energy setting value E input from the operation panel 211, first, the trajectory for extracting the electron beam from the magnitude of the energy E is determined. At this time, when the energy setting value E is small, the electron beam is extracted in a trajectory (n = 1) passing once through the second main electromagnet 107, and when it is large, the electron beam passes twice through the second main electromagnet 107. Orbit (n =
The electron beam is extracted in 2).

The accelerator control device 210 controls the linear accelerator 10
In step 8, the energy V applied to the electron beam is determined. The energy V given by the linear accelerator 108 can be expressed by the following equation 1.

V = E / (n + 1) (1) The accelerator control device 210 determines the electron gun current Ig incident on the linear accelerator 108. However, the linear accelerator 108
The energy V given to the electron beam, the power P of the microwave, and the beam current i in the linear accelerator 108 are expressed by the following equation (2).
It is represented by Here, a and b are constants.

V = a · P ^1/2 −b · i (2) In this embodiment, since the power of the microwave is kept constant and the beam current i in the linear accelerator 108 is changed, the linear accelerator 108 , The beam current i is uniquely determined from the energy V applied to the electron beam. Therefore, in the case of the first orbit, the electron gun current Ig is represented by the following equation 3.

Ig = i / (n + 1) (3) However, the present invention is not limited to this, and only the microwave power P is changed, or both the beam current i and the microwave power P are changed. Needless to say,

Next, the accelerator controller 210 determines the current value of each electromagnet. The current j of the first main electromagnet 106 and the first and second displacement electromagnets 104 and 105 can be expressed by Equation 4 below. Here, c and d are constants for each electromagnet.

J = c · V + d (4) On the other hand, the current K of the second main electromagnet 107 is expressed by the following equation 5 when the electron beam is output in the first pass, and is output in the second pass. In this case, Equation 6 below is obtained.

K = (cV + d) / 2 (5) k = cV + d (6) Setting of all electromagnets including the first and second main electromagnets 106 and 107 set by the above procedure The value is set from the accelerator control device 210 to each electromagnet power supply. Each of the electromagnet power supplies gradually increases the current as shown in FIG. 3A, and sets a preset current value (for example, I _max ).
Is maintained, the current is gradually reduced until the current reaches the current value I ₁ set by the accelerator controller 210 as shown in (2). The accuracy of setting the magnetic flux densities of the first and second main electromagnets 106 and 107 is such that the trajectory of the electron beam is small, that is, the magnetic flux densities of the first and second main electromagnets 106 and 107 can be reduced. It can be lower than the conventional race track type microtron. As a result, the time required for setting the current values of the first and second main electromagnets 106 and 107 can be shortened to a time equivalent to that of the other electromagnets (generally, about 5 seconds). The waiting time accompanying the change in the energy setting value of the line can be greatly reduced.

FIG. 4 is a diagram for explaining the relationship between the magnetic flux density generated by the second main electromagnet and the trajectory of the electron beam. ,
Hereinafter, the operation of the race track type microtron of the present embodiment will be described with reference to FIG.

First, the operation in the case where the output of the electron beam is relatively small, 6 to 14 MeV, will be described with reference to FIG. However, in FIGS. 4A and 4B, the first and second incident correction electromagnets 102 and 1 are shown for simplicity.
03 is omitted. The acceleration by the linear accelerator 108 is 3 MeV in one pass.

The electron beam generated by the electron gun 101 is indicated by an arrow 4
Linear accelerator 1 from the direction indicated by 01 (the direction opposite to the X axis)
08 and accelerated. At this time, the energy level of the electron beam is 3 MeV because only one acceleration is performed by the linear accelerator 108.

The electron beam emitted from the linear accelerator 108 is
The first displacement electromagnet 104 receives a magnetic force in the Y-axis direction perpendicular to the traveling direction, and moves straight in the direction indicated by the arrow 402. The electron beam that has reached the second displacement electromagnet 105 receives a magnetic force from the second displacement electromagnet 105 in a direction opposite to the Y-axis direction, and proceeds straight in a direction opposite to the X-axis indicated by an arrow 403.

The electron beam reaching the first main electromagnet 106 is
As indicated by an arrow 404, the path is reversed by 180 degrees while drawing an arc-shaped trajectory by the magnetic field of the first main electromagnet 106, and then exits the magnetic field range and proceeds straight in the X-axis direction. Thereafter, the electron beam receives a magnetic force in the Y-axis direction by the second displacement electromagnet 105 and proceeds straight in the direction indicated by the arrow 405. The electron beam that has reached the first displacement electromagnet 104 receives a magnetic force in a direction opposite to the Y-axis direction from the first displacement electromagnet 104 and proceeds straight in the X-axis direction indicated by an arrow 406. At this time, the electron beam is accelerated by 3 MeV in the traveling direction by the linear acceleration 108, and becomes 6 MeV.

The electrons accelerated to 6 MeV are indicated by an arrow 407.
As shown by the arrow, while drawing a circular arc locus by the magnetic field of the second main electromagnet 107, after the course is reversed by 180 degrees, it leaves the magnetic field range and goes straight in the direction opposite to the X axis indicated by the arrow 408. Then, it is emitted as a 6 MeV electron beam.

In this case, the output of the linear accelerator 108 is set to 3 MeV. However, it is needless to say that the output of the electron beam can be changed to 6 to 14 MeV by changing the output to 3 to 7 MeV. Absent.

The operation in the case where the output of the electron beam is relatively large, 9 to 21 MeV, will be described with reference to FIG.
However, the acceleration by the linear accelerator 108 is the same as that shown in FIG.
As in the case of (a), 3 MeV is obtained in one pass. The acceleration from the generation of the electron beam to 6 MeV is the same as that of the aforementioned 6
Since it follows the same trajectories 401 to 406 as the acceleration up to Ｍ14 MeV, the following trajectories will be described in the following description.

The electron beam accelerated a second time by the linear accelerator 108 travels straight along the arrow 406 and then draws an arc-shaped trajectory by the magnetic field of the second main electromagnet 107.
The course is reversed by 180 degrees. The electron beam that has escaped from the magnetic field range of the second main electromagnet 107 travels straight in the direction opposite to the X axis indicated by the arrow 409 and reaches the first main electromagnet 106.

The path of the electron beam that has reached the first main electromagnet 106 is reversed again by 180 degrees while drawing a circular locus indicated by an arrow 410 by the magnetic field of the first main electromagnet 106. However, the arc-shaped locus at this time draws an arc larger than the locus indicated by the arrow 404 because the mass of the electron beam is increased.

When the first main electromagnet 106 exits the magnetic field range X
The electron beam that travels straight in the axial direction and reaches the second displacement electromagnet 105 receives a magnetic force in the Y-axis direction due to the magnetic field, and the arrow 41
The vehicle travels straight in a direction slightly displaced in the Y-axis direction from the X-axis direction indicated by 1. The electron beam that has reached the first displacement electromagnet 104 is
The magnetic field receives a magnetic force in a direction opposite to the Y axis, and the traveling direction is displaced in the Y axis direction. The electron beam traveling straight along the trajectory indicated by the arrow 412 is subjected to the third acceleration by the linear accelerator 108, and its energy is accelerated to 9 MeV. The electron beam accelerated by the linear accelerator 108 again has its traveling direction reversed by 180 degrees along the arrow 413 by the magnetic field of the second main electromagnet 107, and then has an energy of 9 MeV along the straight line indicated by the arrow 414. As an electron beam.

In the present embodiment, for simplicity of description, the trajectories of the electrons when passing through the linear accelerator 108 are different from each other. It goes without saying that the vehicle travels straight in the X-axis direction or the direction opposite to the X-axis.

As described above, in the radiotherapy apparatus according to the present embodiment, the size of the magnetic field region of the second main electromagnet 107 in the Y-axis direction is larger than that of the first main electromagnet 106 in the Y-axis direction. To increase the size. The electron beam outlet 202 is arranged on the extension of the race track of the race track type microtron, that is, on the extension of the electron beam deflected by the second main electromagnet 107 on the linear trajectory. When extracting the accelerated electron beam, the accelerator control device 210 controls the second main electromagnet power supply 208 to supply the current to the second main electromagnet 107 according to the output level input from the operation panel 211. Control the amount. Thereby, the trajectory of the electron beam is controlled by changing the magnetic flux density of the second main electromagnet 107, and an electron beam having a desired output is taken out. Since the take-out electromagnet for taking out from the track and the power supply of the take-out electromagnet can be made unnecessary, the configuration of the apparatus can be simplified, and as a result, the race track type microtron can be downsized. Therefore, it becomes possible to incorporate a race track type microtron in the gantry 117 part, which could not be incorporated in the gantry 117 conventionally.

Further, in the radiation therapy apparatus according to the present embodiment, the accelerator controller 210 controls the klystron power supply 115
By controlling the microwave power supplied to the linear accelerator 108, thereby controlling the amount of acceleration in one pass and controlling the magnetic flux density of the second main electromagnet 107 to control the trajectory of the electron beam. Thus, since a configuration is adopted in which a race track corresponding to the energy level of the electron beam to be extracted is selected, a wide range output of 6 to 21 MeV can be performed.

As described above, the invention made by the present inventor is:
Although specifically described based on the embodiments of the present invention, the present invention is not limited to the embodiments of the present invention, and it is needless to say that various modifications can be made without departing from the gist of the present invention. .

[0085]

The effects obtained by typical ones of the inventions disclosed in the present application will be briefly described as follows.

(1) A radiotherapy apparatus in which a race track type microtron is integrated with a gantry can be constructed.

(2) Electrons in a plurality of orbits can be taken out without increasing the size of the main electromagnet.

(3) An electron beam in a plurality of orbits can be taken out without improving the accuracy of the magnetic flux density of the main electromagnet.

(4) The diagnostic efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a schematic configuration of a radiotherapy apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a schematic configuration of a race track type microtron of the present embodiment.

FIG. 3 is a diagram for explaining a relationship between a current value applied to a main electromagnet of the present embodiment and a magnetic flux density.

FIG. 4 is a diagram for explaining a relationship between a magnetic flux density generated by a second main electromagnet and a trajectory of an electron beam according to the present embodiment.

[Explanation of symbols]

101: electron gun, 102: first incident correction electromagnet, 10
3 ... second incident correction electromagnet, 104 ... first displacement electromagnet, 105 ... second displacement electromagnet, 106 ... first main electromagnet, 107 ... second main electromagnet, 108 ... linear accelerator,
109: deflection magnet, 110: target, 111: dose monitor, 112: collimator, 113: electron gun power supply, 1
14 ... klystron, 115 ... klystron power supply,
116 stand, 117 gantry, 118 first trajectory, 119 second trajectory, 120 third trajectory, 20
DESCRIPTION OF SYMBOLS 1 ... Vacuum container, 202 ... Electron beam outlet, 203 ... Power supply for the 1st incidence correction electromagnet, 204 ... Power supply for the 2nd incidence correction electromagnet, 205 ... Power supply for the 1st displacement electromagnet, 206
... power supply for the second displacement electromagnet, 207 ... power supply for the first main electromagnet, 208 ... power supply for the second main electromagnet, 209 ... microwave oscillator, 210 ... accelerator control device, 211 ... operation panel

Claims (1)

[Claims] 1. An electron generating means for generating an electron beam, a linear accelerating means for accelerating the electron beam in a linear direction, a first main electromagnet and a second main electromagnet arranged to face each other via the linear accelerating means. A radiotherapy apparatus having an electromagnet and an electron beam accelerator configured to draw an elliptical orbit between magnetic fields formed by the first main electromagnet and the second main electromagnet. In, the magnetic field region of the second main electromagnet is formed larger than the magnetic field region of the first main electromagnet, and the electron beam A radiotherapy device having an outlet.