JP2013096949A - Scanning type electromagnet and charged particle beam irradiation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure a beam scanning range by taking a uniform magnetic field area as wide in a dual window frame type electromagnet.SOLUTION: Coils 101, 108, 111, 118 are arranged between a first sub area passing through Y direction magnetic field excitation current and a second sub area passing through the Y direction magnetic field excitation current, constituting a first sub area passing through X direction magnetic field excitation current; coils 109, 110, 119, 120 are arranged between main areas 221, 222 passing through the Y direction magnetic field excitation current and the first sub area passing through the Y direction magnetic field excitation current, constituting a second sub area passing through the X direction magnetic field excitation current; coils 201, 208, 211, 218 are arranged between the first sub area passing through the X direction magnetic field excitation current and a second sub area passing through the X direction magnetic field excitation current, constituting the first sub area passing through the Y direction magnetic field excitation current; and coils 209, 210, 219, 220 are arranged between main areas 121, 122 passing through the X direction magnetic field excitation current and the first sub area passing through the X direction magnetic field excitation current, constituting the second sub area passing through the Y direction magnetic field excitation current.

Description

  The present invention relates to a double window frame type electromagnet that can be excited in the X direction and the Y direction by one electromagnet, and a charged particle beam irradiation apparatus including the scanning electromagnet.

  As one of the cancer treatment methods, particle beam therapy is known in which an affected area of a patient is irradiated with an ion beam of protons or carbon ions. When ions such as protons and carbon ions are incident on a substance with high energy, a large dose is given to surrounding substances at the end of the range. Taking advantage of this property, ion beam irradiation is applied to the patient so that the ion beam therapy loses a lot of energy in the cancer cells. This can destroy cancer cells without damaging surrounding healthy tissue. In particle beam therapy, the spatial spread, irradiation position, and energy of the ion beam are adjusted to form a dose distribution that matches the shape of the affected area.

  The particle beam therapy system used for particle beam therapy mainly includes an ion source, an accelerator for accelerating ions generated from the ion source, a beam transport device for transporting an ion beam emitted from the accelerator, and irradiating the affected part with a beam in a desired shape An irradiation device is provided.

  Examples of the accelerator used in the particle beam therapy system include a synchrotron and a cyclotron. Both accelerators share the function of accelerating the incident ions to a predetermined energy and emitting them as ion beams.

  The ion beam emitted from the accelerator is transported to the irradiation device by the beam transport device. The beam transport device is equipped with a deflecting electromagnet that changes the traveling direction of the ion beam, a steering electromagnet, and a quadrupole electromagnet that converges and diverges the ion beam. By appropriately adjusting the excitation amount of these electromagnets A beam of the appropriate size and position is transported to the irradiation device.

  The irradiation device is generally provided in the most downstream in the beam path. In the irradiation apparatus, an ion beam irradiation field is formed in accordance with the shape of the affected part. As an example of a method for forming an irradiation field with an irradiation apparatus, a wobbler method and a scanning irradiation method are known. Both irradiation devices include a scanning electromagnet upstream of the irradiation device, and the beam is deflected when the beam passes through the magnetic field excited by the scanning electromagnet, thereby giving a uniform dose distribution to the affected area.

  In the wobbler method, an energy absorber that adjusts the range of the beam and a collimator that sets the irradiation range are arranged downstream of the scanning electromagnet. The scanning electromagnet generates a magnetic field in the X direction and a magnetic field in the Y direction, and changes the current for exciting each magnetic field with a sine wave, thereby scanning the beam so as to draw a circle in a plane orthogonal to the traveling direction. On the other hand, the beam directed to the outside of the affected area is blocked by the collimator, and a nearly uniform dose distribution is formed in the affected area.

  As an example of the scanning irradiation method, the spot scanning irradiation method will be described. The scanning electromagnet generates a X-direction magnetic field and a Y-direction magnetic field, and controls the amount of current that excites each magnetic field, thereby scanning the beam to irradiate a predetermined spot in a plane orthogonal to the traveling direction. In addition, in order to form an irradiation field that matches the shape of the affected area, the energy of the beam emitted from the accelerator is changed, or the thickness of the energy absorber disposed in the beam transport device is changed, so that it is transported to the irradiation device. Change the energy of the emitted beam. As a result, the position of the Bragg peak changes depending on the energy of the beam, and an irradiation field matching the shape of the affected area is formed. There is also an irradiation device mounted on the rotating gantry to enable irradiation from an arbitrary direction.

  In both the wobbler method and the scanning irradiation method, generally two electromagnets, an electromagnet that excites the X-direction magnetic field and an electromagnet that excites the Y-direction magnetic field, are arranged in series in the beam traveling direction (first conventional technology). .

  By the way, the particle beam therapy system is composed of various devices such as an accelerator, a beam transport device, and an irradiation device, and installation requires a site of several tens of meters. To reduce the cost of the particle beam therapy system, it is effective to reduce the installation area. As one of them, downsizing of the irradiation apparatus is being studied. By reducing the size and weight of the irradiation device, the rotating gantry can be reduced in size and the building can be reduced in size. As a result, the entire system can be reduced in size and cost.

  For example, Non-Patent Document 1 proposes a double window frame type electromagnet (second prior art). This double window frame type electromagnet can excite two magnetic fields of an X direction magnetic field and a Y direction magnetic field with one electromagnet. An arbitrary magnetic field can be excited by vector synthesis of the X direction magnetic field and the Y direction magnetic field. The second prior art using a double window frame type electromagnet is shorter in distance from the scanning electromagnet to the irradiation point than the first prior art in which two electromagnets are arranged in series, and the irradiation apparatus is downsized. Can do.

Vladimir Anferov et al. "Combined XY scanning magnet for conformal proton radiation therapy" Medical Physics 32 (3), March 2005

  However, in the double window frame type electromagnet (second prior art), coils of different systems interfere with each other to generate a so-called hexapole magnetic field and do not become a uniform magnetic field region in the peripheral portion. A beam deviating from the uniform magnetic field region may not be able to give a dose according to the irradiation plan to the affected area because the beam size changes from the original value. As a result of not being able to obtain a large uniform magnetic field region, the beam passing region inside the scanning electromagnet has to be narrower than that of the first prior art, and the beam scanning range is limited.

  In the case of the first prior art using two electromagnets, an electromagnet that excites an X-direction magnetic field and an electromagnet that excites a Y-direction magnetic field, the magnetic pole width of each electromagnet is made longer than the gap of the coil (XY asymmetry). As a result, the above problems can be reduced.

  However, since the double window frame type electromagnet excites the magnetic field in two directions of the X direction magnetic field and the Y direction magnetic field, the magnetic pole shape is symmetric with respect to X and Y (symmetric with respect to the straight line Y = X). As in the first prior art, it cannot be made XY asymmetry.

  An object of the present invention is to provide a double window frame type electromagnet that excites two magnetic fields, an X direction magnetic field and a Y direction magnetic field, by widening a uniform magnetic field region, thereby exciting the X direction magnetic field and the Y direction magnetic field. It is to provide a scanning electromagnet that can maintain a beam scanning range equivalent to that in the case of using two electromagnets of the electromagnet that excites (a first prior art).

  (1) In order to achieve the above object, the present invention includes a plurality of X-direction magnetic field excitation coils wound around a magnetic pole and a plurality of Y-direction magnetic field excitation coils wound around the magnetic pole. A heavy window frame type electromagnet, wherein the current flows through the plurality of X direction magnetic field excitation coils within the magnetic poles from an X direction magnetic field excitation current passing main region and an X direction magnetic field excitation current passing subregion. The region in the magnetic pole, in which current flows through the plurality of Y-direction magnetic field excitation coils, includes a Y-direction magnetic field excitation current passing main region and a Y-direction magnetic field excitation current passing sub-region, and the X direction The magnetic field excitation current passing sub-region is disposed between the Y-direction magnetic field excitation current passing main region and the Y-direction magnetic field excitation current passing sub-region, and is generated in the X-direction magnetic field excitation current passing main region during X-direction magnetic field excitation. The Y-direction magnetic field excitation current passing sub-region is disposed between the X-direction magnetic field excitation current-passing main region and the X-direction magnetic field excitation current-passing sub-region. Sometimes, the influence of the X-direction magnetic field generated in the Y-direction magnetic field excitation current passing main region is reduced.

  In the present invention configured as described above, for example, in the case of Y-direction magnetic field excitation, the X-direction magnetic field excitation current passing sub-region adjacent to the Y-direction magnetic field excitation current passing main region is not excited. Therefore, the magnetic field in the X direction is reduced compared to the prior art.

  Further, the Y-direction magnetic field excitation current passage sub-region adjacent to the X-direction magnetic field excitation current passage main region acts to change the direction of the magnetic field generated in the X direction to the Y direction.

  By these actions, the influence of the hexapole magnetic field is reduced, and a large uniform magnetic field region can be obtained as compared with the second prior art. That is, a uniform magnetic field region equivalent to the first prior art can be obtained.

  (2) In the above (1), preferably, the magnetic pole is a cylindrical body having a square section.

  Since the magnetic pole cross section is square, the double window frame type electromagnet has an X / Y symmetrical cross section.

  (3) In the above (2), preferably, the X-direction magnetic field excitation current passing sub-region is composed of an X-direction magnetic field excitation current passing first sub-region and an X-direction magnetic field excitation current passing second sub-region, The Y-direction magnetic field excitation current passage sub-region includes a Y-direction magnetic field excitation current passage first sub-region and a Y-direction magnetic field excitation current passage second sub-region, and the X-direction magnetic field excitation current passage main region has the square shape. The Y-direction magnetic field excitation current passing main region is disposed on the other opposite sides of the square, and the X-direction magnetic field excitation current passing first sub-region is disposed in the Y direction. The magnetic field excitation current passage first sub-region and the Y-direction magnetic field excitation current passage second sub-region are disposed, and the X-direction magnetic field excitation current passage second sub-region is formed between the Y-direction magnetic field excitation current passage main region and the Y-direction magnetic field excitation current passage main region. The Y-direction magnetic field excitation current passage first sub-region is disposed between the X-direction magnetic field excitation current passage first sub-region and the X-direction magnetic field excitation current passage second sub-region. The Y-direction magnetic field excitation current passage second subregion is disposed between the X-direction magnetic field excitation current passage main region and the X-direction magnetic field excitation current passage first subregion.

  (4) In the above (1), preferably, the magnetic pole is a cylindrical body.

  Due to the circular cross section of the magnetic pole, the double window frame type electromagnet has an X / Y symmetrical cross section.

  (5) The scanning electromagnet of (1) is preferably provided in a charged particle beam irradiation apparatus.

  The irradiation apparatus can be reduced in size by the double window frame type electromagnet. As a result, the entire system can be reduced in size and cost.

  According to the present invention, by using a double window frame type electromagnet, compared to the case of using two electromagnets, an electromagnet that excites an X-direction magnetic field and an electromagnet that excites a Y-direction magnetic field (first prior art), irradiation is performed. The size of the apparatus can be reduced.

  In addition, by changing the coil arrangement of the second conventional technique, a uniform magnetic field region can be widened and the beam scanning range equivalent to the first conventional technique can be maintained.

It is a schematic block diagram of a particle beam therapy system. It is a schematic block diagram of an irradiation apparatus (1st Embodiment). It is sectional drawing of a scanning electromagnet (1st Embodiment). It is sectional drawing of a scanning electromagnet (prior art). It is a figure which shows the magnetic field distribution of a X direction (Y direction excitation). It is a figure which shows the magnetic field distribution of a Y direction (Y direction excitation). It is a figure which shows a Y direction magnetic field (1st Embodiment). It is sectional drawing of a scanning electromagnet (2nd Embodiment). It is a schematic block diagram of an irradiation apparatus (3rd Embodiment). It is sectional drawing of a scanning electromagnet (3rd Embodiment). It is sectional drawing of a scanning electromagnet (prior art and cylindrical body). It is a figure which shows the magnetic field distribution of a X direction (Y direction excitation). It is a figure which shows the magnetic field distribution of a Y direction (Y direction excitation).

<First Embodiment>
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

~Constitution~
FIG. 1 is a schematic configuration diagram of a particle beam therapy system 100 in the present embodiment. The system 100 includes an ion source 200, an incident accelerator 300, a main accelerator 400, a beam transport device 500, and an irradiation device 600. This system 100 is a treatment apparatus using proton beams, and hydrogen ions, that is, protons are generated by the ion source 200 and ions preliminarily accelerated by the incident accelerator 300 are incident on the main accelerator 400. In the main accelerator 400, the beam is accelerated to the energy that matches the range of the beam planned by the treatment plan for each patient, and is emitted to the beam transport device 500. The emitted beam is adjusted to an appropriate size by the beam transport device 500 and transported to the irradiation device 600. The beam transport apparatus 500 has a rotating gantry 510, and the beam transport apparatus 500 and the irradiation apparatus 600 connected thereto rotate around the rotating shaft 520. Thereby, the irradiation point 700 is irradiated with the beam from the irradiation direction determined by the treatment plan for each patient.

  FIG. 2 is a schematic configuration diagram of the irradiation apparatus 600. The irradiation device 600 is a scanning irradiation method irradiation device. A beam is incident from above and is deflected by a force from a magnetic field component perpendicular to the beam trajectory by the scanning electromagnet 610, so that the irradiation point 700 can be scanned within a predetermined scanning range 710. A beam position monitor 620 for confirming the beam position is installed downstream of the scanning electromagnet 610. During irradiation, the beam position that has passed through the sensitive part 621 is measured by this monitor 620, and the irradiation position is confirmed. Yes.

  In FIG. 2, only a part of the coil of the scanning electromagnet 610 is illustrated. The scanning electromagnet 610 is provided with an X-direction magnetic field excitation coil 611 and a Y-direction magnetic field excitation amount coil 612. Each of the coils 611 and 612 has an X-direction magnetic field excitation power source (not shown) and a Y-direction magnetic field excitation. A power source (not shown) is connected to each other, and a current pattern calculated by a command from the control device is output according to the beam irradiation position and irradiation path for each patient planned by the treatment planning device.

  The magnetic pole 613 has a cylindrical body with a square cross section, and is a laminate of electromagnetic steel plates having a window frame shape thickness of about 0.5 mm. The planar shape is a square, and the beam passage region 615 is also a square. The length of the irradiation device 600 is determined by the ratio between the magnetic field of the scanning electromagnet and the irradiation field size. For example, a proton beam with a one-side beam size of 5 mm and a kinetic energy of 220 MeV is scanned with an electromagnet having a maximum magnetic field of 0.2 T and a magnetic pole length of 700 mm within a square range of 400 mm on a side. The distance between the end face on the downstream side of the scanning electromagnet and the irradiation point is 2900 mm. On the other hand, the uniform magnetic field region 615 is a square with a side of 54 mm.

  An X-direction magnetic field excitation coil 611 and a Y-direction magnetic field excitation coil 612 are wound around the magnetic pole 613.

  FIG. 3 is a cross-sectional view of the scanning electromagnet 610. The X-direction magnetic field excitation coil 611 is composed of a plurality of coils, and the coils 101 to 120 in the magnetic poles are shown as plain. The Y-direction magnetic field excitation coil 612 includes a plurality of coils, and the coils 201 to 220 in the magnetic poles are indicated by hatching. The characteristic configuration of the present invention resides in the arrangement of each coil.

  The coils 102 to 107 are disposed on the upper side of the illustrated square, and the coils 112 to 117 are disposed on the lower side of the illustrated square to configure the X-direction magnetic field excitation current passing main regions 121 and 122. Coils 202 to 207 are arranged on the right side of the square in the figure, and coils 212 to 217 are arranged on the left side of the square in the figure to constitute the Y-direction magnetic field excitation current passing main regions 221 and 222.

  On the upper side of the illustrated square, the coil 101 is disposed between the coil 218 and the coil 219, the coil 108 is disposed between the coil 201 and the coil 220, and on the lower side of the illustrated square, the coil 111 is connected to the coil 208. The coil 118 is disposed between the coil 209, and the coil 118 is disposed between the coil 211 and the coil 210. Each of the coils 118 constitutes an X-direction magnetic field excitation current passing first subregion.

  On the right side of the square, the coil 109 is disposed between the main region 221 and the coil 201, the coil 110 is disposed between the main region 221 and the coil 208, and on the left side of the square, the coil 119 is disposed on the main region. The coil 120 is disposed between the main region 222 and the coil 218, and each constitutes an X-direction magnetic field excitation current passing second sub-region.

  On the right side of the square shown, the coil 201 is disposed between the coil 108 and the coil 109, the coil 208 is disposed between the coil 111 and the coil 110, and on the left side of the square illustrated, the coil 211 is composed of the coil 118 and the coil 110. The coil 218 is disposed between the coil 101 and the coil 120, and constitutes a Y-direction magnetic field excitation current passing first sub-region.

  On the upper side of the square shown in the figure, the coil 219 is arranged between the main area 121 and the coil 101, the coil 220 is arranged between the main area 121 and the coil 108, and on the lower side of the square shown in the figure, the coil 209 is connected to the main area 121. It arrange | positions between the area | region 122 and the coil 111, and the coil 210 is arrange | positioned between the main area | region 122 and the coil 118, and each comprises the Y direction magnetic field excitation current passage 2nd sub area | region.

  In the X-direction magnetic field excitation coil 611, a circuit is configured in which a power supply to the coils 101 to 120 are sequentially connected in series and returned to the power supply. When a current is passed through the X direction magnetic field excitation coil 611, the magnetic field is excited in the X direction shown in the figure. In the Y-direction magnetic field excitation coil 612, a circuit is configured in which the coils 201 to 220 are sequentially connected in series from another power source and returned to the power source. When a current is passed through the Y-direction magnetic field excitation coil 612, the magnetic field is excited in the Y direction shown in the figure. Connections between coils passing through different coil passage regions are made via a coil connection portion 614 (see FIG. 2) outside the magnetic pole.

-Action and effect-
The effect of this embodiment will be described by comparing with a double window frame type electromagnet (second prior art) according to the prior art.

  FIG. 4 is a cross-sectional view of a scanning electromagnet according to the prior art. The Y-direction magnetic field excitation coils 231, 232, 233, and 234 are disposed at the positions where the X-direction magnetic field excitation coils 109, 110, 119, and 120 according to this embodiment are disposed, and the Y-direction magnetic field excitation coil 219 according to this embodiment. , 220, 209, 210 are arranged in the X direction magnetic field exciting coils 131, 132, 133, 134.

  That is, in the prior art, an X-direction magnetic field excitation current passing region is configured in the entire upper and lower sides of the square, and a Y-direction magnetic field excitation current passing region is configured in the entire right and left sides of the square. There is no division such as main area and sub area (all main areas).

  By the way, the maximum relative permeability of a magnetic material such as iron or electromagnetic steel is about 5000 to 8000. A magnetic field generated around a magnetic body having such a high relative permeability is generated in a direction substantially perpendicular to the surface of the magnetic body. Using this property, a window frame type electromagnet uses a magnetic body having a rectangular opening as a magnetic pole. For example, a vertical magnetic field can be excited in the opening by flowing currents in opposite directions to excitation coils provided at the left and right ends of the rectangular opening.

  In a double window frame type electromagnet that excites a magnetic field in two directions of an X-direction magnetic field and a Y-direction magnetic field, the shapes of the magnetic pole and the opening are square. When a current is passed through the X direction magnetic field excitation coil 611, the magnetic field is excited in the X direction shown in the figure. When a current is passed through the Y direction magnetic field excitation coil 612, the magnetic field is excited in the Y direction shown in the figure.

  The problems of the prior art will be described. For example, when a magnetic field is excited in the Y direction by the Y-direction magnetic field excitation coil 612, the magnetic field is a dipole magnetic field. However, a slight X-direction magnetic field is generated around the Y-direction magnetic field exciting coil 612. This X-direction magnetic field increases toward the end of the opening so as to be proportional to the square of the distance from the center. As a result, the magnetic field in the X direction around the coils 201, 208, 211, and 218 cannot be ignored and becomes a so-called hexapole magnetic field. An outline of the generated magnetic field is added to FIG.

Since the X direction magnetic field is about 10 ⁻² to 10 ^{−1 with} respect to the Y direction magnetic field, a large uniform magnetic field region 615 cannot be obtained. This problem will be described in more detail with reference to FIGS.

  FIG. 5 is a diagram showing the magnetic field distribution in the X direction, and FIG. 6 is a diagram showing the magnetic field distribution in the Y direction. In both cases, the magnetic field normalized by the central magnetic field when the magnetic field in the Y direction is excited by the Y-direction magnetic field exciting coil 612 is shown. The magnetic field distribution of the prior art is shown by a solid line.

  In both the X and Y directions, as the distance from the center increases, the influence of the hexapole magnetic field increases and the magnetic field is not uniform.

  On the other hand, the configuration of the present embodiment operates as follows.

  FIG. 7 is obtained by adding an outline of the magnetic field in the Y direction generated by the Y direction magnetic field exciting coil 612 to the sectional view of the scanning electromagnet 610 (FIG. 3). The X direction magnetic field excitation coils 109 and 110 adjacent to the main region 221 and the X direction magnetic field excitation coils 119 and 120 adjacent to the main region 222 are not excited. Therefore, the magnetic field in the X direction is reduced compared to the prior art.

  Further, the Y-direction magnetic field excitation coils 219 and 220 adjacent to the main region 121 and the Y-direction magnetic field excitation coils 209 and 210 adjacent to the main region 122 act to change the direction of the magnetic field generated in the X direction to the Y direction. To do.

  By these actions, the influence of the hexapole magnetic field is reduced, and a larger uniform magnetic field region 615 is obtained as compared with the prior art. This effect will be described in more detail with reference to FIGS. 5 and 6 show the magnetic field distribution of the present embodiment by broken lines.

  In both the X and Y directions, as the distance from the center increases, the influence of the hexapole magnetic field increases and the tendency to lose the uniform magnetic field is the same as in the prior art. However, it can be seen that the magnetic field is more uniform in the X and Y directions in a wider range than the conventional technique (the standard magnetic field is close to 1). Therefore, a larger uniform magnetic field region 615 is obtained.

  Although the case of Y-direction magnetic field excitation has been described, the same applies to the case of X-direction magnetic field excitation.

  Moreover, this embodiment can achieve size reduction of an irradiation apparatus by using a double window frame type electromagnet.

Second Embodiment
~Constitution~
FIG. 8 is a cross-sectional view of the scanning electromagnet according to the second embodiment. The Y-direction magnetic field excitation coils 231, 232, 233, and 234 are disposed at the arrangement positions of the X-direction magnetic field excitation coils 109, 110, 119, and 120 of the first embodiment (see FIG. 3). X-direction magnetic field excitation coils 131, 132, 133, and 134 are disposed at positions where the Y-direction magnetic field excitation coils 219, 220, 209, and 210 are disposed. Furthermore, Y-direction magnetic field excitation coils 236, 237, 238, and 239 are disposed at the positions where the X-direction magnetic field excitation coils 101, 108, 111, and 118 according to the first embodiment are arranged, and the Y-direction magnetic field according to the first embodiment. X-direction magnetic field excitation coils 136, 137, 138, and 139 are arranged at positions where the excitation coils 201, 208, 211, and 218 are arranged.

  In other words, the Y-direction magnetic field excitation coils 236, 237, 238, and 239 are arranged at the arrangement positions of the X-direction magnetic field excitation coils 101, 108, 111, and 118 of the conventional technique (see FIG. 4). X direction magnetic field excitation coils 136, 137, 138, and 139 are disposed at the positions where the directional magnetic field excitation coils 201, 208, 211, and 218 are disposed.

  That is, the coils 131, 102 to 107, 132 are disposed on the upper side of the illustrated square, and the coils 133, 112 to 117, 134 are disposed on the lower side of the illustrated square, and the X direction magnetic field excitation current passing main regions 121, 122 are disposed. Is configured. Coils 231, 202 to 207, 232 are arranged on the right side of the illustrated square, and coils 233, 212 to 217, 234 are arranged on the left side of the illustrated square to constitute the Y direction magnetic field excitation current passing main regions 221, 222. ing.

  On the right side of the illustrated square, the coil 136 is disposed between the main region 221 and the coil 237, the coil 137 is disposed between the main region 221 and the coil 238, and on the left side of the illustrated square, the coil 138 is disposed on the main region. The coil 139 is disposed between the main region 222 and the coil 236, and constitutes an X-direction magnetic field excitation current passing sub-region.

  The coil 236 is disposed between the main region 121 and the coil 139 on the upper side of the illustrated square, the coil 237 is disposed between the main region 121 and the coil 136, and the coil 238 is disposed on the lower side of the illustrated square. The coil 239 is disposed between the region 122 and the coil 137, and the coil 239 is disposed between the main region 122 and the coil 138, and each constitutes a Y-direction magnetic field excitation current passing sub-region.

-Action and effect-
As in the first embodiment, the operation and effect of this embodiment will be described by taking the case of Y-direction magnetic field excitation as an example. An outline of the generated magnetic field in the Y direction is added to FIG.

  The X direction magnetic field excitation coils 136 and 137 adjacent to the main region 221 and the X direction magnetic field excitation coils 138 and 139 adjacent to the main region 222 are not excited. Therefore, the magnetic field in the X direction is reduced compared to the prior art.

  Further, the Y-direction magnetic field excitation coils 236 and 237 adjacent to the main region 121 and the Y-direction magnetic field excitation coils 238 and 239 adjacent to the main region 122 act to change the direction of the magnetic field generated in the X direction to the Y direction. To do.

  By these actions, the influence of the hexapole magnetic field is reduced, and a larger uniform magnetic field region 615 is obtained as compared with the prior art (see FIG. 4). Although the case of Y-direction magnetic field excitation has been described, the same applies to the case of X-direction magnetic field excitation.

<Third Embodiment>
~Constitution~
In the first embodiment and the second embodiment, the present invention is applied to a cylindrical magnetic pole 613 having a square section, whereas in the third embodiment, the present invention is applied to a cylindrical magnetic pole 616. Is.

  FIG. 9 is a schematic configuration diagram of the irradiation apparatus 600. The uniform magnetic field region 617 has a circular shape with a side of 27 mm so that the beam is scanned in a range 720 having a radius of 200 mm with respect to the irradiation point 700.

  FIG. 10 is a cross-sectional view of a scanning electromagnet 610 according to the third embodiment. The X-direction magnetic field excitation coil 611 is composed of a plurality of coils, and the coils 151 to 166 in the magnetic poles are shown as plain. The Y-direction magnetic field exciting coil 612 is composed of a plurality of coils, and the coils 251 to 266 in the magnetic pole are indicated by hatching.

  Here, the X axis is set to 0 °, and the angle is defined counterclockwise. For convenience of explanation, the range of 45 ° to 135 ° is the upper side of the circumference of the drawing, the range of 135 ° to 225 ° is the left side of the circumference of the drawing, the range of 225 ° to 315 ° is the lower side of the circumference of the drawing, 315 ° to 405 ° ( The range of 45 ° is referred to as the right side in the figure.

  Coils 151 to 156 are arranged on the upper side in the figure, and coils 159 to 164 are arranged on the lower side in the figure to configure the X-direction magnetic field excitation current passing main regions 171 and 172. Coils 252 to 257 are arranged on the right side in the figure, and coils 260 to 265 are arranged on the left side in the figure to constitute the Y-direction magnetic field excitation current passing main regions 271 and 272.

  On the right side of the illustrated circle, the coil 157 is disposed between the main region 271 and the coil 251, the coil 158 is disposed between the main region 271 and the coil 258, and on the left side of the illustrated circle, the coil 165 is Arranged between the main region 272 and the coil 259, the coil 166 is disposed between the main region 272 and the coil 266, and each constitutes an X-direction magnetic field excitation current passing sub-region.

  On the upper side in the figure, the coil 266 is disposed between the main area 171 and the coil 166, the coil 251 is disposed between the main area 171 and the coil 157, and on the lower side in the figure, the coil 258 is The coil 259 is disposed between the main region 172 and the coil 165, and constitutes a Y-direction magnetic field excitation current passing sub-region.

-Action and effect-
The effect of this embodiment will be described by comparing with the prior art. The conventional magnetic pole 613 is a cylindrical body having a square cross section. However, assuming that the coil arrangement according to the conventional technique (see FIG. 4) is applied to the magnetic pole 616 of the cylindrical body, the prior art of this embodiment is used. And

  FIG. 11 is a cross-sectional view of a scanning electromagnet when a coil arrangement according to the prior art is applied to a magnetic pole 616 of a cylindrical body. Y direction magnetic field excitation coils 281, 282, 283, and 284 are disposed at positions where the X direction magnetic field excitation coils 157, 158, 165, and 166 of the present embodiment are disposed, and the Y direction magnetic field excitation coil 251 of the present embodiment. , 258, 259, and 266 are arranged X-direction magnetic field exciting coils 181, 182, 183, and 184.

  That is, in the prior art, an X-direction magnetic field excitation current passing region is configured in the entire upper and lower sides of the circumference, and a Y-direction magnetic field excitation current passing region is configured in the entire right and left sides of the circumference. There is no division such as main area and sub area.

  For example, when a magnetic field is excited in the Y direction by the Y-direction magnetic field excitation coil 612, the magnetic field is a dipole magnetic field. However, a slight X-direction magnetic field is generated around the Y-direction magnetic field exciting coil 612. This X-direction magnetic field increases toward the end of the opening so as to be proportional to the square of the distance from the center. As a result, the magnetic field in the X direction around the coils 281, 282, 283, and 284 is not negligible, and becomes a so-called hexapole magnetic field, and a large uniform magnetic field region 617 cannot be obtained. This problem will be described in more detail with reference to FIGS.

  FIG. 12 is a diagram illustrating the magnetic field distribution in the X direction, and FIG. 13 is a diagram illustrating the magnetic field distribution in the Y direction. In both cases, the magnetic field normalized by the central magnetic field when the magnetic field in the Y direction is excited by the Y-direction magnetic field exciting coil 612 is shown. The magnetic field distribution of the prior art is shown by a solid line.

  In both the X and Y directions, as the distance from the center increases, the influence of the hexapole magnetic field increases and the magnetic field is not uniform. An outline of the generated magnetic field is added to FIG.

  On the other hand, the magnetic field distribution of this embodiment is indicated by a broken line. In both the X and Y directions, as the distance from the center increases, the influence of the hexapole magnetic field increases and the tendency to lose the uniform magnetic field is the same as in the prior art. However, it can be seen that the magnetic field is more uniform in the X and Y directions in a wider range than the conventional technique (the standard magnetic field is close to 1).

  An outline of the magnetic field in the Y direction generated in this embodiment is added to FIG.

  The X direction magnetic field excitation coils 157 and 158 adjacent to the main region 271 and the X direction magnetic field excitation coils 165 and 166 adjacent to the main region 272 are not excited. Therefore, the magnetic field in the X direction is reduced compared to the prior art.

  Further, the Y-direction magnetic field excitation coils 251 and 266 adjacent to the main region 171 and the Y-direction magnetic field excitation coils 258 and 259 adjacent to the main region 172 act to change the direction of the magnetic field generated in the X direction to the Y direction. To do.

  By these actions, the influence of the hexapole magnetic field is reduced, and a larger uniform magnetic field region 617 is obtained as compared with the conventional technique (see FIG. 11). Although the case of Y-direction magnetic field excitation has been described, the same applies to the case of X-direction magnetic field excitation.

DESCRIPTION OF SYMBOLS 100 Particle beam therapy system 200 Ion source 300 Incident accelerator 400 Main accelerator 500 Beam transport device 510 Rotating gantry 520 Rotating gantry rotating shaft 600 Irradiating device 610 Scanning electromagnets 611, 101-184 X-direction magnetic field exciting coils 612, 201-284 Y direction magnetic field exciting coil 613, 616 Magnetic pole 614 Coil connection portion 615, 617 Uniform magnetic field region 616 Scanning magnet central axis 620 Beam position monitor 700 Irradiation point 710, 720 Beam scanning range

Claims (5)

A double window frame type electromagnet comprising a plurality of X direction magnetic field excitation coils wound around a magnetic pole and a plurality of Y direction magnetic field excitation coils wound around the magnetic pole;
A region in the magnetic pole, in which a current flows through the plurality of X-direction magnetic field excitation coils, includes an X-direction magnetic field excitation current passing main region and an X-direction magnetic field excitation current passing sub-region,
A region in the magnetic pole, in which a current flows through the plurality of Y-direction magnetic field excitation coils, includes a Y-direction magnetic field excitation current passing main region and a Y-direction magnetic field excitation current passing sub-region,
The X-direction magnetic field excitation current passage sub-region is disposed between the Y-direction magnetic field excitation current passage main region and the Y-direction magnetic field excitation current passage sub-region, and the X-direction magnetic field excitation current passage main region during X-direction magnetic field excitation. Reduce the influence of the Y-direction magnetic field generated in the
The Y-direction magnetic field excitation current passage sub-region is disposed between the X-direction magnetic field excitation current passage main region and the X-direction magnetic field excitation current passage sub-region, and the Y-direction magnetic field excitation current passage main region at the time of Y-direction magnetic field excitation. The scanning electromagnet characterized by reducing the influence of the X direction magnetic field which generate | occur | produces. The scanning electromagnet according to claim 1, wherein
The magnetic pole is a cylindrical body having a square cross section. The scanning electromagnet according to claim 2, wherein
The X-direction magnetic field excitation current passage sub-region is composed of an X-direction magnetic field excitation current passage first sub-region and an X-direction magnetic field excitation current passage second sub-region,
The Y-direction magnetic field excitation current passage sub-region is composed of a Y-direction magnetic field excitation current passage first sub-region and a Y-direction magnetic field excitation current passage second sub-region,
The X-direction magnetic field excitation current passing main region is disposed on one opposite side of the square,
The Y-direction magnetic field excitation current passing main region is disposed on the opposite side of the square,
The first X direction magnetic field excitation current passing sub-region is disposed between the first Y direction magnetic field excitation current passing sub region and the second Y direction magnetic field excitation current passing sub region.
The X direction magnetic field excitation current passing second sub-region is disposed between the Y direction magnetic field excitation current passing main region and the Y direction magnetic field excitation current passing first sub region,
The Y direction magnetic field excitation current passing first sub-region is disposed between the X direction magnetic field excitation current passing first sub region and the X direction magnetic field excitation current passing second sub region,
The Y-direction magnetic field excitation current passage second subregion is disposed between the X-direction magnetic field excitation current passage main region and the X-direction magnetic field excitation current passage first subregion. The scanning electromagnet according to claim 1, wherein
The scanning electromagnet, wherein the magnetic pole is a cylindrical body.   A charged particle beam irradiation apparatus comprising the scanning electromagnet according to claim 1.

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