Charged particle beam irradiation system, offset device, and control method

Abstract

To provide a charged particle beam irradiation system which suppresses a dispersion function appearing in a charged particle beam at an isocenter without having to provide a charged particle beam irradiation device with a quadrupole electromagnet behind an electromagnet provided to direct the charged particle beam to the isocenter.SOLUTION: A charged particle beam irradiation system is provided, comprising an accelerator, an electromagnet capable of deflecting a charged particle beam emitted from the accelerator, a charged particle beam irradiation device configured to irradiate an isocenter with the charged particle beam from multiple directions, and an offset unit configured to provide control to suppress a dispersion function generated by the electromagnet at the isocenter.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a charged particle beam irradiation system that suppresses the dispersion function when the charged particle beam reaches the isocenter. [Background technology]

[0002] Conventionally, particle beam therapy using charged particle beams has been used as one of the cancer treatments. In particle beam therapy, a method of irradiating the lesion with charged particle beams from multiple directions is generally used to increase the dose concentration while minimizing the influence on the surrounding normal tissue. As such an irradiation device, a rotating gantry that irradiates the patient's lesion from all directions is known.

[0003] The charged particle beam generated by the accelerator is transported to the rotating gantry, which is the therapeutic irradiation section, through a transport path that includes bending electromagnets for changing the traveling direction of the charged particle beam, quadrupole electromagnets for converging or diverging the charged particle beam, steering electromagnets for finely adjusting the traveling direction of the charged particle beam, etc. The charged particle beam transported to the rotating gantry is scanned by a scanning electromagnet, and the lesion is divided into multiple layers in the traveling direction of the charged particle beam, and three-dimensional therapeutic irradiation is performed.

[0004] In particle beam therapy, it is required to irradiate the charged particle beam with high irradiation position accuracy and stable treatment irradiation with a desired beam shape at the isocenter in the treatment room. Incidentally, the charged particle beam extracted from the accelerator has a certain dispersion function before reaching the isocenter. The dispersion function is a coefficient that represents the correlation of the position deviation from the designed orbit caused by the deviation of the momentum of each charged particle that composes the charged particle beam. This dispersion function is generated by the charged particle beam passing through the bending electromagnet, and as a result, the irradiation position of the charged particle beam is shifted from the isocenter, or the shape of the charged particle beam is deformed from the desired shape. Therefore, the dispersion function of the charged particle beam needs to be as close to 0 as possible at the isocenter, and it is generally known that this dispersion function can be adjusted by using a quadrupole electromagnet.

[0005] Patent Document 1 discloses an example of a charged particle beam irradiation device that uses a fixed port in a fixed vertical direction, and discloses a technology for adjusting the dispersion function by providing a bending electromagnet and a quadrupole electromagnet on a plane inclined from the horizontal plane.

[0006] On the other hand, in the case of a rotating gantry, irradiation of the charged particle beam from multiple directions is realized by using bending electromagnets. Since multiple bending electromagnets are installed in the rotating gantry to adjust the traveling direction of the charged particle beam, a dispersion function occurs in the direction in which the charged particle beam is deflected in each bending electromagnet. Therefore, in the rotating gantry, the dispersion function of the charged particle beam is adjusted within the rotating gantry. Patent Document 2 discloses a technology for adjusting the dispersion function by providing multiple quadrupole electromagnets in the rotating gantry.

[0007] A technique for irradiating a lesion with a charged particle beam from multiple directions without using a rotating gantry is described in Patent Document 3. In Patent Document 3, irradiation from multiple directions is achieved by providing a bending electromagnet at the end of the transport path of the charged particle beam, but the bending electromagnet generates a dispersion function in the vertical direction. However, in Patent Document 3, the placement of a quadrupole electromagnet for the purpose of making this dispersion function zero at the isocenter causes a problem of an increase in the size of the irradiation device. The same is true in Patent Document 2, where the placement of the quadrupole electromagnet leads to an increase in the size of the rotating gantry. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2015-000090 A [Patent Document 2] Patent No. 2019-082389 [Patent Document 3] Patent No. 6387476 Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, the present invention has been made in consideration of the above problems, and has an object to provide a charged particle beam irradiation system that can adjust the dispersion function generated by the bending electromagnets without placing a quadrupole electromagnet in the irradiation section of the charged particle beam irradiation device. [Means for solving the problem]

[0010] In order to address the above problems, a charged particle beam irradiation system according to one embodiment of the present invention includes an accelerator, an electromagnet capable of deflecting a charged particle beam extracted from the accelerator, a charged particle beam irradiation device that irradiates the charged particle beam from multiple directions toward an isocenter, and an offset unit that controls the dispersion function generated by the electromagnet so that it is suppressed at the isocenter. Effect of the Invention

[0011] According to the charged particle beam irradiation system of the present invention, the dispersion function caused by the influence of the bending magnets provided in the irradiation section can be suppressed at the isocenter without providing a quadrupole magnet in the irradiation section. Also, by not providing a quadrupole magnet in the irradiation section, it is possible to prevent the irradiation section from becoming enlarged. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing a configuration example of a charged particle beam irradiation system according to the first embodiment. [Diagram 2] FIG. 2 is a block diagram illustrating an example of the configuration of the offset unit. [Diagram 3] FIG. 3 is a diagram for explaining a mechanism for irradiating a charged particle beam by the charged particle beam irradiation device. [Figure 4] FIG. 4 is a top view of a configuration example of the charged particle beam irradiation system according to the first embodiment. [Diagram 5] FIG. 5(a) is a diagram showing a schematic example of a dispersion function when an offset section is not used, and FIG. 5(b) is a diagram showing a schematic example of a dispersion function when an offset section is used. [Figure 6] FIG. 6 shows a configuration example of a charged particle beam irradiation system according to the second embodiment in the case where a rotating gantry is used. [Figure 7] 7(a) and (b) are diagrams showing modified examples of the offset portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the charged particle beam irradiation system according to this embodiment will be described in detail with reference to the drawings.

[0014] <Embodiment 1> Fig. 1 is a block diagram showing a schematic configuration example of a charged particle beam irradiation system according to embodiment 1. As shown in Fig. 1, an example will be described in which an irradiation device for irradiating a charged particle beam according to embodiment 1 does not rotate around a patient but can irradiate a focus from multiple directions (within a range of approximately a semicircle).

[0015] As shown in FIG. 1, the charged particle beam irradiation system includes an accelerator 1, an offset unit 100, a distribution magnet 70, and a charged particle beam irradiation device 50 including a deflection magnet 80. As shown in FIG. 1, in the charged particle beam irradiation system, the accelerator 1, the offset unit 100, the distribution magnet 70, and the charged particle beam irradiation device 50 are connected in this order, and the charged particle beam is transported from the accelerator 1 to a lesion (isocenter) of a patient placed on a treatment table 15 of an automobile 10 in a treatment room 30 and irradiated. In the first embodiment, in the path in which the charged particle beam is transported from the accelerator 1 to the isocenter O, the accelerator 1 side may be referred to as the upstream side, and the isocenter side may be referred to as the downstream side. In the charged particle beam irradiation device 50, the charged particle beam may be irradiated from the irradiation nozzle 11 toward the isocenter.

[0016] The accelerator 1 is a device having a function of accelerating charged particles to generate a charged particle beam. The accelerator 1 may be realized by, for example, a synchrotron, a cyclotron, a linear accelerator, etc., but is not limited to these. The accelerator 1 transmits the generated charged particle beam to the offset unit 100.

[0017] A transport path may be provided between the accelerator 1 and the offset unit 100 as a transmission path for transporting the charged particle beam. This transport path deflects the charged particle beam extracted from the accelerator 1 as necessary and transmits it to a desired position, i.e., the entrance port of the offset unit 100. Such a transport path may include a bending electromagnet, a quadrupole electromagnet, a steering electromagnet, and the like as necessary.

[0018] The offset unit 100 is a device provided to suppress the dispersion function generated in the irradiation device, and is a device for intentionally generating a dispersion function in the charged particle beam in advance so that the dispersion function generated in the irradiation device is as close to zero as possible at the isocenter. As described above, the dispersion function is a coefficient that represents the correlation of the positional deviation from the design orbit caused by the deviation of the momentum of each charged particle constituting the charged particle beam, and when the charged particle beam is deflected by a deflection electromagnet, the positional deviation occurs from the desired position, and indicates the value of the positional deviation. Naturally, the smaller the positional deviation, the better, and it is preferably 0. Therefore, suppressing the dispersion function means making the value of the dispersion function as close to 0 as possible (i.e., making the positional deviation of the charged particle beam from the isocenter when passing through the isocenter small). The charged particle beam from the accelerator 1 is incident on the offset unit 100 via a transport path as necessary.

[0019] FIG. 2 is a block diagram showing a detailed configuration example of the offset unit 100. As shown in FIG. 2, the offset unit 100 includes a first deflection electromagnet 101, a quadrupole electromagnet 102, a second deflection electromagnet 103, and an offset control unit 110. In the offset unit 100, as shown in FIG. 2, a charged particle beam from the accelerator 1 is incident on the first deflection electromagnet 101 of the offset unit 100. The charged particle beam deflected by the first deflection electromagnet 101 is adjusted by the quadrupole electromagnet 102. Then, the charged particle beam adjusted by the quadrupole electromagnet 102 is deflected again by the second deflection electromagnet 103. As for the dispersion function generated in the offset unit 100, as shown in FIG. 2, the first deflection electromagnet 101, the quadrupole electromagnet 102, and the second deflection electromagnet 103 are controlled by the offset control unit 110 that can control the offset unit 100. The offset control unit 110 may be a computer system that calculates the excitation amount of the quadrupole electromagnet 102 based on the deflection angle and irradiation angle of the distribution electromagnet 70 and the bending electromagnet 80 and instructs the quadrupole electromagnet 102 of the excitation amount, and may execute the process by a program or the like stored in a memory (not shown), or may be realized by a dedicated circuit that executes the control. Furthermore, the offset control unit 110 may also control the first bending electromagnet 101 and the second bending electromagnet 103.

[0020] Generally, when transporting a charged particle beam, the charged particle beam output from an accelerator may be transported to a target position by inserting a configuration in which a first bending electromagnet, a quadrupole electromagnet, and a second bending electromagnet are arranged in this order. In this case, when the charged particle beam is deflected by the upstream bending electromagnet, i.e., the first bending electromagnet, a dispersion function and a gradient are generated. Here, depending on the excitation amount of the quadrupole electromagnet, the charged particle beam can be transported in a state in which no dispersion function is generated by setting the excitation amount to 0 after passing through the downstream bending electromagnet, i.e., the second bending electromagnet, in other words, under double achromatic conditions.

[0021] However, in the offset unit 100 according to this embodiment, the sorting electromagnet 70 and the bending electromagnet 80 are provided downstream (rear stage) of the path along which the charged particle beam is transported. Therefore, it is necessary to take into consideration the dispersion function that occurs when the charged particle beam is deflected in the sorting electromagnet 70 and the bending electromagnet 80. That is, the offset unit control unit of the offset unit 100 needs to be in an achromatic condition, including the offset unit 100, the sorting electromagnet 70, and the bending electromagnet 80.

[0022] Specifically, the dispersion function of the charged particle beam after passing through the offset unit 100 is intentionally not set to 0, and the excitation amount of the quadrupole electromagnet 102 is adjusted so that the dispersion function already has a predetermined value at the deflection starting point Q of the sorting electromagnet 70. That is, the offset control unit 110 acquires in advance information on how much the charged particle beam is deflected in the sorting electromagnet 70 and the deflection electromagnet 80, and controls the excitation amount of the quadrupole electromagnet 102 by performing a back calculation based on the acquired information so that the value of the dispersion function to be generated in the charged particle beam after passing through the offset unit 100 becomes the value.

[0023] In this control, the offset control unit 110 may calculate in advance, by simulation, the excitation amount of the quadrupole electromagnet 102 according to the value of the dispersion function to be generated for each of a plurality of combinations of the deflection angle and the irradiation angle by the sorting electromagnet 70 and the bending electromagnet 80, and store and control each combination as a control table, thereby appropriately controlling the excitation amount of the quadrupole electromagnet 102. Alternatively, the offset control unit 110 may input the deflection angle of the sorting electromagnet 70 and the irradiation angle of the bending electromagnet 80, hold a function for calculating the excitation amount of the quadrupole electromagnet 102, and control so as to apply the excitation amount calculated from the function to the quadrupole electromagnet 102. Alternatively, a trained model that has learned the relationship between the combination of the deflection angle and the irradiation angle of the sorting electromagnet 70 and the bending electromagnet 80 and the corresponding desired excitation amount of the quadrupole electromagnet 102 may be used, and the deflection angle and the irradiation angle may be input to the trained model to obtain the excitation amount. The details of the deflection starting point Q, the deflection angle in the deflection electromagnet 70, and the irradiation angle in the deflection electromagnet 80 will be described later.

[0024] The charged particle beam, in which a dispersion function has been generated by the offset unit 100, reaches the isocenter via the distribution electromagnet 70 and the bending electromagnet 80. When the charged particle beam is made to travel in a straight line, the offset unit 100 controls the beam so that no dispersion function is generated (becomes 0) when the beam is output from the second bending electromagnet 103, and the charged particle beam without a dispersion function is incident on the distribution electromagnet 70.

[0025] Here, the deflection of the charged particle beam by the deflection electromagnet 70 and the deflection electromagnet 80 will be described in detail with reference to FIG.

[0026] FIG. 3 is a diagram for explaining the details of the distribution electromagnet 70 and the bending electromagnet 80. FIG. 3(a) is a schematic diagram showing the path of the charged particle beam when the charged particle beam irradiation device 50 of the charged particle beam irradiation system is viewed from the side. As shown in FIG. 3(a), the charged particle beam irradiation device 50 includes a distribution electromagnet 70 and a bending electromagnet 80. As shown in FIG. 1, a part of the charged particle beam irradiation device 50 is exposed in the treatment room 30, and another part is buried in the wall of the treatment room 30 or underground. As shown in FIG. 1, the bending electromagnet of the charged particle beam irradiation device 50 is partially buried in the wall or underground, and the distribution electromagnet 70 is also provided outside the treatment room 30.

[0027] FIG. 3(a) shows examples of multiple beam paths that differ for each deflection angle φ and convergence angle θ. Here, the traveling direction of the charged particle beam is the X-axis, the direction of the magnetic field generated by the deflection electromagnet 80 is the Z-axis, and the direction perpendicular to the X-axis and Z-axis is the Y-axis. The deflection electromagnet 80 is configured to converge the charged particle beam incident from a wide range of deflection angles φ with respect to the X-axis on the XY plane to the isocenter O. In other words, when the charged particle beam is not deflected by the distribution electromagnet and the deflection electromagnet 80, the charged particle beam passes through the distribution electromagnet and the deflection electromagnet 80 in a straight line and reaches the isocenter. In FIG. 3(a), the irradiation nozzle 11 is omitted, and for the sake of simplicity, the isocenter O is set as the origin of the XYZ space, and the upstream side (the accelerator side, the left side of the paper in FIG. 3(a)) is set as the positive direction of the X-axis.

[0028] 3A, the sorting electromagnet 70 deflects the incident charged particle beam as necessary. In some cases, the sorting electromagnet 70 causes the incident charged particle beam to travel in a straight line without deflecting it.

[0029] The range of the deflection angle φ is between more than -90 degrees and less than +90 degrees, and the positive (+Y-axis direction) deflection angle range and the negative (-Y-axis direction) deflection angle range may be different (asymmetric). For example, the maximum deflection angle on the positive side (φ=φMAX) may be any of 10 degrees, 15 degrees, 20 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees, 45 degrees, 50 degrees, 60 degrees, 70 degrees, 80 degrees, and 85 degrees, and the maximum deflection angle on the negative side (φ=-φMAX) may be any of -10 degrees, -15 degrees, -20 degrees, -25 degrees, -30 degrees, -35 degrees, -40 degrees, -45 degrees, -50 degrees, -60 degrees, -70 degrees, -80 degrees, and -85 degrees. Note that the deflection angle φ is not limited to these angles. The charged particle beam is deflected by the distribution electromagnet 70 and the deflection electromagnet 80, and is incident on the isocenter while tracing various trajectories as shown in FIG. 3(a). That is, the charged particle beam can be made to pass through any one of a plurality of trajectories by the charged particle beam irradiation device 50, and the charged particle beam can be irradiated on the isocenter from a plurality of directions. Note that FIG. 3(a) shows a state in which the distribution electromagnet 70 immediately deflects the charged particle beam at a desired deflection angle φ, but this is for ease of viewing the drawing. In reality, the distribution electromagnet 70 gradually starts deflecting the charged particle beam at the deflection origin Q, and as a result, the charged particle beam is emitted at a deflection angle φ with respect to the X-axis.

[0030] The deflection electromagnet 80 includes one or more coil pairs, which generate a uniform magnetic field (effective magnetic field regions 81a, 81b) that is oriented in a direction perpendicular to the traveling direction of the charged particle beam and the spreading direction of the deflection angle φ of the charged particle beam (Z-axis direction in the figure), and are arranged to sandwich the path of the charged particle beam. The effective magnetic field region generated by one coil pair of the deflection electromagnet 80 has a crescent shape in the XY plane as shown in FIG. 3(a), and the details will be described later. Note that the gap between the opposing coil pairs through which the charged particle beam passes (the distance in the Z-axis direction) is sufficiently small compared to the range in which the charged particle beam spreads on the XY plane, so the spread of the charged particle beam in the Z-axis direction is not considered here.

[0031] 3(b) is a cross-sectional view of the deflection electromagnet 80 taken along line AA. The deflection electromagnet 80 preferably includes at least two coil pairs 84a, 84b. Magnetic poles 85a, 85b are incorporated inside the coils 84a, 84b, respectively, and a yoke 86 is connected to the magnetic poles 85a, 85b. A power supply unit (not shown) is connected to the deflection electromagnet 80, and when a current (excitation current) is supplied from the power supply unit to the coil pairs 84a, 84b, the deflection electromagnet 80 is excited, and effective magnetic field regions 81a, 81b (collectively referred to as effective magnetic field region 81) are formed.

[0032] The range of the effective magnetic field region 81a and the range of the effective magnetic field region 81b may be different (asymmetric). For example, if the range of the positive (+Y-axis) deflection angle φ and the range of the negative (-Y-axis) deflection angle φ are asymmetric, the effective magnetic field regions 81a and 81b can be formed asymmetrically accordingly, thereby reducing the unused effective magnetic field region.

[0033] The deflection angle φ of the charged particle beam deflected by the deflection electromagnet 70 and incident on the deflection electromagnet 80 ranges from the maximum positive deflection angle (φ=φMAX) to the maximum negative deflection angle (φ=-φMAX), where the maximum positive deflection angle φMAX is an angle of 10 degrees or more and less than 90 degrees, and the maximum negative deflection angle -φMAX is an angle of more than -90 degrees and less than -10 degrees. The deflection angle φ and the irradiation angle θ, which will be described later, are angles of the path of the charged particle beam with respect to the X-axis on the XY plane.

[0034] The charged particle beam incident in the positive deflection angle range (φ=0 or more to φMAX) is deflected by the effective magnetic field region 81a of the first coil pair 84a, passes through the irradiation nozzle 11, and is irradiated to the isocenter O. The charged particle beam incident in the negative deflection angle range (φ=less than 0 to -φMAX) is deflected by the effective magnetic field region 81b of the second coil pair 84b, passes through the irradiation nozzle 11, and is irradiated to the isocenter O. The magnetic fields of the effective magnetic field region 81a and the effective magnetic field region 81b are directed in opposite directions. The charged particle beam incident on the bending electromagnet 80 from the distribution electromagnet 70 at a deflection angle φ=0 passes through either one of the effective magnetic field regions 81a and 81b, or between both regions 81a and 81b, and is converged to the isocenter O through the irradiation nozzle (not shown).

[0035] The deflection angle φ of the charged particle beam incident on the deflection electromagnet 80 is controlled by the deflection electromagnet 70. The deflection electromagnet 70 generates a magnetic field oriented in a direction (Z-axis in the figure) perpendicular to the traveling direction (X-axis in the figure) of the charged particle beam supplied from an accelerator (not shown), and includes an electromagnet that deflects the passing charged particle beam, and a control unit that controls the strength and direction of the magnetic field (both not shown). The deflection electromagnet 70 deflects the charged particle beam in the XY plane by controlling the strength and direction (Z-axis direction) of the magnetic field, and emits the charged particle beam deflected at the deflection angle φ at the deflection origin Q to the deflection electromagnet 80. Here, the deflection origin Q and the isocenter O are on the X-axis (on the same horizontal plane).

[0036] 3(c), a formula for forming the effective magnetic field region 81a of the deflection electromagnet 80 will be described. In this embodiment, the deflection of the charged particle beam in the Z-axis direction is not taken into consideration, so the formation of the effective magnetic field region in the XY plane will be described. The effective magnetic field region 81a of the deflection electromagnet 80 will be described, but the same applies to the effective magnetic field region 81b, so the description will be omitted.

[0037] First, the boundaries of the effective magnetic field region 81a on the emission side 83 of the deflection electromagnet 80 for the charged particle beam are determined to be within a range at an equal distance r1 from the isocenter O. Next, the boundaries of the effective magnetic field region 81a on the incidence side 82 of the deflection electromagnet 80 for the charged particle beam are determined based on the relational expressions (1) to (5) described later so that the incident charged particle beam is deflected at a deflection angle φ at an imaginary deflection origin Q located at a predetermined distance L from the isocenter O and converges on the isocenter O. Here, the imaginary deflection origin Q is a point at the center of the distribution electromagnet 70 where it is assumed that the charged particle beam receives a kick of the deflection angle φ over an extremely short distance.

[0038] The charged particle beam transported at a deflection angle φ enters from an arbitrary point P1 on the boundary of the effective magnetic field region 81a on the entrance side 82, performs a circular motion with a radius of curvature r2 within the effective magnetic field region 81a (the central angle at this time is (φ+θ)), exits from a point P2 on the boundary of the effective magnetic field region 81a on the exit side 83, and is irradiated toward the isocenter O. In other words, points P1 and P2 are on an arc with a radius r2 and a central angle of (φ+θ).

[0039] 3(c), an XY coordinate system is assumed with the isocenter O as the origin on the XY plane. If the angle between the X-axis and a line connecting point P2 on the emission side 83 and the isocenter O is defined as the irradiation angle θ, the coordinates (x, y) of point P1 on the incidence side 82, the deflection angle φ, and the distance R between point Q and point P1 can be calculated from the following relational expressions (1) to (4).

[0040]

number

[0041] Here, a magnetic field with a uniform magnetic flux density B is generated in the effective magnetic field region 81a, and if the momentum of the charged particle beam is p (which roughly depends on the accelerator) and the charge is q, the radius of curvature r2 of the charged particle beam deflected in the magnetic field is expressed by equation (5).

[0042]

number

[0043] Based on the above relational expressions (1) to (5), the shape and arrangement of the coil pair 84a and the magnetic pole 85a of the deflection electromagnet 80 are adjusted, and the current flowing through the coil pair 84a is adjusted, so that the shape of the boundary of the effective magnetic field region 81a can be adjusted. That is, the boundary is determined so that the distance between any point P2 on the boundary of the effective magnetic field region 81a on the exit side 83 and the isocenter O is equal to r1, r2 is determined from equation (5) by adjusting the magnetic flux density B of the effective magnetic field region 81a, and the boundary of the effective magnetic field region 81a on the entrance side 82 is determined so that the distance R between the point P1 on the boundary of the effective magnetic field region 81a on the entrance side 82 and the deflection origin Q has the relationship of equation (4). The maximum value of φ in equation (3) is the maximum deflection angle φMAX. Although not limited thereto, it is preferable to adjust the positions of the deflection origin Q, the bending electromagnet 80, and the isocenter O so that the charged particle beam passing through the deflection origin Q converges to the isocenter O without being deflected by the bending electromagnet 80, since this makes it possible to simplify the device configuration.

[0044] The boundary between the effective magnetic field regions 81a, 81b of the deflection electromagnet 80 obtained as described above is an ideal shape for converging the charged particle beam to the isocenter O. In reality, even if there is a deviation from this ideal shape or non-uniformity in the magnetic field distribution, the excitation amount (magnetic flux density B) of the deflection electromagnet 80 is finely adjusted in advance for each deflection angle φ, the information is stored in a power supply device, and the deflection angle φ and the amount of current of the deflection electromagnet 80 are controlled so as to be linked to each other, thereby deflecting the charged particle beam to match the isocenter O. In addition, when the non-uniformity of the magnetic field distribution can be predicted in advance, the trajectory of the charged particle beam can be finely adjusted by correcting the shape and arrangement of the coil pair 84a, 84b and the magnetic poles 85a, 85b of the deflection electromagnet 80.

[0045] This allows the charged particle beam to be irradiated at a desired angle to the affected area (isocenter O).

[0046] Fig. 4 is a top view showing a schematic diagram of a charged particle beam irradiation system. As shown in Fig. 4, in the charged particle beam irradiation system, at least the offset unit 100, the distribution electromagnet 70, and the bending electromagnet 80 are arranged in a straight line. That is, the deflection direction of the charged particle beam deflected by the distribution electromagnet 70 and the bending electromagnet 80 is a vertical direction. In the charged particle beam irradiation system, the accelerator 1 may or may not be arranged in a straight line with the offset unit 100, the distribution electromagnet 70, and the bending electromagnet 80.

[0047] <Dispersion function> The dispersion function will be described with reference to Fig. 5. Fig. 5(a) is a diagram for explaining the dispersion function when the offset section 100 is not present, and Fig. 5(b) is a diagram for explaining the dispersion function when the offset section 100 is present.

[0048] The upper part of FIG. 5(a) is a schematic diagram showing the configuration of a charged particle beam irradiation system without an offset unit 100, and shows an example of a distribution electromagnet 70, a bending electromagnet 80, and a trajectory of a charged particle beam irradiated to an isocenter via these. Here, the lower part of FIG. 5(a) shows an example of a dispersion function of a charged particle beam, and shows an example of a correspondence between the distribution electromagnet 70, the bending electromagnet 80, and the isocenter. As shown in the graph of the dispersion function in the lower part of FIG. 5(a), a dispersion function is generated in the charged particle beam by being deflected via the distribution electromagnet 70. Similarly, the charged particle beam deflected by the distribution electromagnet 70 is also deflected by the bending electromagnet 80 and moves toward the isocenter O. At this time, a dispersion function is further generated in the charged particle beam by being deflected by the bending electromagnet 80. As a result, as shown in the lower part of FIG. 5(a), the dispersion function may not be 0 at the isocenter, that is, it may have a value. The fact that the dispersion function has a value means that there is a possibility that position fluctuation occurs due to fluctuation in the momentum of the charged particle beam extracted from the accelerator 1, and the charged particle beam may not be irradiated to the focus. The dispersion function in the lower part of Fig. 5(a) shows the fluctuation in the value of the dispersion function of the charged particle beam in the vertical direction.

[0049] On the other hand, the upper part of Fig. 5(b) is a schematic diagram showing the configuration of a charged particle beam irradiation system without the offset unit 100, and shows an example of the trajectory of the charged particle beam irradiated to the isocenter via the offset unit 100, the distribution electromagnet 70, and the bending electromagnet 80. The lower part of Fig. 5(b) shows an example of the dispersion function of the charged particle beam, and shows an example of the correspondence between the distribution electromagnet 70, the bending electromagnet 80, and the isocenter. As shown in the graph of the dispersion function in the lower part of Fig. 5(b), the dispersion function occurs in the charged particle beam by being deflected by the first bending electromagnet 101 and the second bending electromagnet 103 provided in the offset unit 100.

[0050] In the rear stage of the offset unit 100 in the upper stage of FIG. 5(b), when the charged particle beam is deflected toward the isocenter by the distribution electromagnet 70 and the bending electromagnet 80, a dispersion function is naturally generated. Although the value of this dispersion function varies depending on the degree to which the charged particle beam is deflected in the distribution electromagnet 70 and the bending electromagnet 80, it is possible to calculate it by simulating the characteristics of the distribution electromagnet 70 and the bending electromagnet 80 in advance. In the offset unit 100, a dispersion function is generated in advance so that the dispersion function generated in the distribution electromagnet 70 and the bending electromagnet 80 becomes 0 at the isocenter. That is, as shown in FIG. 5(b), the dispersion function of the charged particle beam has a predetermined value at the timing of incidence on the distribution electromagnet 70. In this manner, by emitting a charged particle beam having a dispersion function in the offset section 100 and injecting it into the distribution electromagnet 70, the dispersion function of the charged particle beam irradiated to the isocenter O in the charged particle beam irradiation device 50 can be suppressed, preferably set to zero.

[0051] <Summary> As shown in the first embodiment, the dispersion function generated when the charged particle beam is deflected using the distribution magnet 70 and the deflection magnet 80 arranged in the charged particle beam irradiation device 50 is intentionally generated in the offset unit 100 arranged in front of the distribution magnet 70, and the dispersion function at the isocenter O can be made zero by making the charged particle beam incident on the distribution magnet 70. Therefore, in the charged particle beam irradiation device 50, that is, in the treatment room 30, it is possible to converge the charged particle beam to the isocenter O (suppress the dispersion function of the charged particle beam at the isocenter O, and preferably make it zero) without arranging a quadrupole magnet for making the dispersion function zero. Therefore, by not arranging a quadrupole magnet, it is possible to prevent the charged particle beam irradiation device 50 from becoming enlarged. As a result, it is possible to make the treatment room 30 compact.

[0052] <Embodiment 2> In the second embodiment, a case will be described in which the charged particle beam irradiation device is a rotating gantry that rotates around the patient.

[0053] FIG. 6 is a block diagram showing a schematic configuration of a charged particle beam irradiation system according to the second embodiment. The difference between the block diagram shown in FIG. 6 and the block diagram shown in FIG. 1 is the difference in the charged particle beam irradiation device, and the other configurations are the same as those of the first embodiment. As shown in FIG. 6, the charged particle beam irradiation system includes an accelerator 1, a first offset unit 100a, a second offset unit 100b, and a rotating gantry 500. The rotating gantry 500 corresponds to the charged particle beam irradiation device in the second embodiment. In the second embodiment, the rotating gantry 500 can irradiate the charged particle beam from a plurality of directions toward the isocenter by rotating the irradiation nozzle 91 (irradiation unit) around the patient. In FIG. 6, an incidence path 601 along which the charged particle beam is incident on the rotating gantry 500 also indicates the rotation axis of the rotating gantry 500.

[0054] In the second embodiment, the accelerator 1 is similar to that in the first embodiment, and therefore a description thereof will be omitted.

[0055] The first offset unit 100a is also similar to the offset unit 100 in the above-mentioned embodiment 1, and is composed of a first deflection electromagnet 101a, a quadrupole electromagnet 102a, and a second deflection electromagnet 103a, and deflects the charged particle beam in the vertical direction to emit a charged particle beam that generates a desired dispersion function in the vertical direction.

[0056] The second offset unit 100b has a configuration in which a quadrupole electromagnet is arranged between two deflection electromagnets, similar to the first offset unit 100a, and is arranged in this order, i.e., a third deflection magnet 101b, a quadrupole electromagnet 102b, and a fourth deflection electromagnet 103b, and is arranged on the path of the charged particle beam. However, the second offset unit 100b has a configuration in which the entire configuration is rotated 90 degrees with respect to the first offset unit 100a. That is, the first offset unit 100a deflects the charged particle beam in the vertical direction to generate a dispersion function in the vertical direction, whereas the second offset unit 100b deflects the charged particle beam in the horizontal direction to generate a dispersion function in the horizontal direction. That is, the first offset unit 100a can be rephrased as a vertical offset unit, and the second offset unit 100b can be rephrased as a horizontal offset unit. This allows the rotating gantry 500 to be adjusted to suppress (preferably make zero) the dispersion function at isocenter 0 in both the vertical and horizontal directions, regardless of how tilted it is relative to the patient.

[0057] In this case, regarding the control of the charged particle beam in the vertical direction by the first offset unit 100a, the offset control unit 110a may, for example, calculate the excitation amount of the quadrupole electromagnet 102a according to the value of the dispersion function to be generated for various rotation angles of the rotating gantry 500 centered on the axis 601 and based on, for example, the horizontal direction by simulation, store the combination as a control table, and control it to appropriately control the excitation amount of the quadrupole electromagnet 102a. In this way, the first offset unit 100a can control the dispersion function in the vertical direction. Alternatively, a trained model that has learned the relationship between the rotation angle of the axis 601 and the corresponding desirable excitation amount of the quadrupole electromagnet 102 may be used, and the rotation angle from the reference position of the rotating gantry 500 may be input to the trained model to obtain the excitation amount of the quadrupole electromagnet 102b. Note that, although the rotation angle is used here, this may be replaced by, for example, the coordinate value of the irradiation nozzle 91 of the rotating gantry 500.

[0058] Similarly, for the control of the charged particle beam in the vertical direction by the second offset unit 100b, the offset control unit 110b may, for example, calculate the excitation amount of the quadrupole electromagnet 102b according to the value of the dispersion function to be generated for various rotation angles of the rotating gantry 500 centered on the axis 601 and based on, for example, the vertical direction (or the horizontal direction), by simulation, store the combination as a control table, and control it to appropriately control the excitation amount of the quadrupole electromagnet 102a. In this way, the second offset unit 100b can control the dispersion function in the horizontal direction. Alternatively, a trained model that has trained the relationship between the rotation angle of the axis 601 and the corresponding desired excitation amount of the quadrupole electromagnet 102b may be used, and the rotation angle from the reference position of the rotating gantry 500 may be input to the trained model to obtain the excitation amount of the quadrupole electromagnet 102b. Although the rotation angle is used here, this may be replaced by, for example, the coordinate value of the irradiation nozzle 91 of the rotating gantry 500.

[0059] That is, in the second embodiment, an offset unit control unit (not shown) controls the first offset unit 100a and the second offset unit 100b. The offset control units 110a and 110b control the excitation amounts of the quadrupole electromagnets of the first offset unit 100a and the second offset unit 100b so that a charged particle beam having a dispersion function already generated at the timing of incidence on the rotating gantry 500 is incident so that both the vertical component and the horizontal component of the dispersion function generated by the rotation angle of the rotation axis 601 in the rotating gantry 500 and the multiple bending electromagnets provided in the rotating gantry 500 are suppressed (preferably to be zero) at the isocenter.

[0060] As a result, even when a rotating gantry is used, a charged particle beam with a dispersion function of zero can be irradiated at the isocenter without providing a quadrupole electromagnet in the irradiation nozzle 91 .

[0061] <Summary> As shown in the second embodiment, even in a charged particle beam irradiation system in which a rotating gantry including a deflection magnet is used as an irradiation device, by providing two offset units for deflecting in the vertical and horizontal directions, it is possible to suppress the dispersion function of the charged particle beam at the isocenter, preferably to make it 0, without disposing a quadrupole magnet in the irradiation device, as in the first embodiment. Therefore, it is possible to suppress the enlargement of the irradiation device.

[0062] <Modification> The charged particle beam irradiation system and the offset unit 100 shown in the above embodiment are not limited to the aspects shown in the above embodiment. They can be appropriately modified within the knowledge of those skilled in the art. Various modified examples will be described below.

[0063] (1) In the above embodiment, the basic configuration of the offset unit 100 is described as being configured in such a manner that a quadrupole electromagnet is sandwiched between two bending electromagnets. However, the configuration of the offset unit 100 is not limited to the form shown in the above embodiment.

[0064] 7(a), the offset unit 100 may also be configured to include quadrupole electromagnets 104, 105 downstream (on the charged particle beam irradiation device side) of the second deflection electromagnet 103. Here, an example is shown in which two quadrupole electromagnets 104, 105 are provided, but the number of quadrupole electromagnets is not limited to two, and may be one, or three or more.

[0065] The role of the quadrupole electromagnets 104 and 105 in the transport path is to suppress the divergence of the charged particle beam having a dispersion function in the second bending electromagnet 103, which would result in an increase in loss during transport, and to adjust the charged particle beam.

[0066] In addition, in FIG. 7(a), the offset unit 100 is shown as being disposed between the accelerator 1 and the sorting electromagnet 70, but it goes without saying that the configuration shown in FIG. 7(a) can also be used as the offset units 100a, 100b in the above-mentioned embodiment 2.

[0067] (2) In the above embodiment, one offset unit 100 is provided. This allows the charged particle beam to be adjusted in the height direction and incident on the charged particle beam irradiation device. On the other hand, there are cases where it is desired to give the charged particle beam emitted from the offset unit 100 a dispersion function without changing the height of the charged particle beam and to function as an offset unit, that is, to make the dispersion function of the charged particle beam at the isocenter zero.

[0068] In such a case, the configuration can be realized by using the configuration shown in FIG.

[0069] That is, a second offset section 100c may be provided that has the same configuration as the first offset section 100a and is arranged symmetrically to the first offset section 100a in the traveling direction of the charged particle beam. The first offset section 100a is composed of a first deflection electromagnet 101a, a quadrupole electromagnet 102a, and a second deflection electromagnet 103a, and this configuration is the same as that of the offset section 100 shown in the first embodiment.

[0070] On the other hand, as shown in FIG. 7(b), the second offset section 100c is configured to be symmetrical to the first offset section 100a at the center of the paper, and is configured such that a first deflection electromagnet 101c, a quadrupole electromagnet 102c, and a second deflection electromagnet 103c are provided facing the second deflection electromagnet 103a.

[0071] In the offset section, since two bending electromagnets are used, the incident position of the charged particle beam in the up-down direction (vertical direction) inevitably shifts between the time of incidence and the time of extraction, but with the configuration of Fig. 7(b), the charged particle beam can be controlled so that the dispersion function of the charged particle beam does not shift in the up-down direction and becomes 0 at the isocenter O. In the case of Fig. 7(b), the offset control section controls the excitation amount of the quadrupole electromagnets 102a and 102c of both the first offset section 100a and the second offset section 100c.

[0072] (3) In the above-mentioned first and second embodiments, the offset units 100, 100a, and 100b are provided on the path before the electromagnets (distributing electromagnets, deflecting electromagnets, etc.) in the case where the charged particle beam is deflected by electromagnets (distributing electromagnets, deflecting electromagnets, etc.) after the offset unit 100 on the path until the charged particle beam is transported from the accelerator 1 to the isocenter, and a dispersion function is generated in the charged particle beam, and when a quadrupole electromagnet for adjusting the dispersion function after the deflection is not provided, or cannot be provided, or is difficult to provide, the offset units 100, 100a, and 100b are preferably provided at the final stage (the most downstream position) of the path on which the charged particle beam is transported from the accelerator 1 to the charged particle beam irradiation device 50 or the rotating gantry 500. [Explanation of symbols]

[0073] 1 accelerator 10 Mobile vehicles 11 Irradiation nozzle 30 treatment room 15 Treatment table 50 Charged particle beam irradiation device 70 vibration separation electromagnet 80 deflection electromagnet 100 offset section 101 first deflection electromagnet 102 quadrupole electromagnet 103 second deflection electromagnet 104 quadrupole electromagnet 105 quadrupole electromagnet 110 offset control unit 100a first offset section 101a first deflection electromagnet 102a quadrupole electromagnet 103a second deflection electromagnet 100b second offset section 101b first deflection electromagnet 102b quadrupole electromagnet 103b second deflection electromagnet 100c second offset section 101c first deflection electromagnet 102c quadrupole electromagnet 103c second deflection electromagnet 500 rotating gantry

Claims

1. The accelerator and an electromagnet capable of deflecting the charged particle beam extracted from the accelerator; a charged particle beam irradiation device that irradiates an isocenter with charged particle beams from multiple directions; An offset unit is provided to control the dispersion function generated by the electromagnet so that it is suppressed at the isocenter. Charged particle beam irradiation system.

2. The offset portion is a first bending electromagnet; A quadrupole electromagnet, a second bending electromagnet; a control unit that generates a dispersion function for the charged particle beam input to the offset unit so that a dispersion function generated by the electromagnet is suppressed, The first bending electromagnet, the quadrupole electromagnet, and the second bending electromagnet are arranged in this order on the path of the charged particle beam.

2. The charged particle beam irradiation system according to claim 1, wherein the charged particle beam irradiation system comprises: a first electrode;

3. the charged particle beam irradiation device includes, as the electromagnets, a deflecting electromagnet and a bending electromagnet that can deflect the charged particle beam in a vertical direction; The first and second deflection electromagnets of the offset section can deflect the charged particle beam in a vertical direction.

3. The charged particle beam irradiation system according to claim 2, wherein the charged particle beam irradiation system comprises: a first electrode;

4. the charged particle beam irradiation device includes a bending electromagnet capable of deflecting the charged particle beam, a rotating gantry in which an irradiation nozzle that irradiates the isocenter with the charged particle beam rotates; The offset portion is a first offset unit including a first deflection electromagnet and a second deflection electromagnet capable of deflecting the charged particle beam in a vertical direction, with a quadrupole electromagnet inserted therebetween; a second offset portion including a third deflection electromagnet and a fourth deflection electromagnet capable of deflecting the charged particle beam in the horizontal direction, with a quadrupole electromagnet inserted therebetween; 3. The charged particle beam irradiation system according to claim 2, wherein the charged particle beam irradiation system comprises: a first electrode;

5. The control unit controls the offset unit so that the value of the dispersion function becomes 0.

3. The charged particle beam irradiation system according to claim 2, wherein the charged particle beam irradiation system comprises: a first electrode;

6. In a path through which the charged particle beam passes from the accelerator to the isocenter, no quadrupole electromagnet is disposed after the electromagnet.

6. The charged particle beam irradiation system according to claim 1, wherein the charged particle beam irradiation system comprises: a first electrode;

7. An offset device disposed on a path of a charged particle beam exiting an accelerator for suppressing a dispersion function of the charged particle beam at an isocenter, the offset device comprising: a first bending electromagnet; A quadrupole electromagnet, a second bending electromagnet; a control unit that generates a dispersion function in the charged particle beam by the second bending electromagnet so that the dispersion function of the charged particle beam that has passed through the second bending electromagnet and is irradiated onto an isocenter via the sorting electromagnet and the bending electromagnet is suppressed, The first bending electromagnet, the quadrupole electromagnet, and the second bending electromagnet are arranged in this order. Offset device.

8. 1. A computer-based control method for an offset unit in a charged particle beam irradiation system including an accelerator, an electromagnet capable of deflecting a charged particle beam extracted from the accelerator, a charged particle beam irradiation device that irradiates an isocenter with the charged particle beam from a plurality of directions, and an offset unit that controls the offset unit so that a dispersion function generated by the electromagnet is suppressed at the isocenter, the method comprising: a receiving step of receiving input of deflection information regarding deflection in the electromagnet; a control step of controlling the dispersion function generated by the electromagnet so as to be suppressed at the isocenter based on the deflection information; A control method comprising:

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