JP7722698B2 - Charged particle beam irradiation device and charged particle beam therapy system - Google Patents

Description

The present invention relates to a charged particle beam irradiation device and a charged particle beam therapy system.

Particle beam therapy has traditionally been used to treat malignant tumors, such as cancer, by irradiating them with a beam of charged particles (also known as a "particle beam") accelerated to high energy. When an object is irradiated with a charged particle beam, energy (dose) is imparted to the object along the path of the charged particle beam within the object. When concentrating the dose on a limited area (target) within the object, the charged particle beam is irradiated from various directions so that it overlaps with the target, thereby increasing the concentration of the dose.

Patent Document 1 discloses a charged particle beam irradiation device equipped with a focusing electromagnet that deflects a charged particle beam incident from a wide angle range and focuses the beam at the isocenter.
Patent Document 2 discloses the selection of a plurality of independent beam paths within a treatment room.

Patent No. 6364141 Japanese Patent Application Laid-Open No. 2002-113118

In a charged particle beam irradiation device in which multiple beam paths for irradiating a charged particle beam exist within the same treatment room (in the case of Patent Document 1, the area through which the beam travels downstream from the deflection origin Q), when irradiating a charged particle beam through a predetermined beam path, there is a risk that the charged particle beam may travel through an unintended beam path and be unintentionally irradiated onto the patient.

In light of these circumstances, the present invention aims to provide a charged particle beam irradiation device that prevents such unintended irradiation.

The present invention includes the following aspects [1] to [5].
[1]
A charged particle beam irradiation device,
a beam transport system (30) having a plurality of beam paths for transporting the charged particle beam emitted from the accelerator (20) to one isocenter (O);
a shield (110) disposed on a first beam path among the plurality of beam paths and configured to block travel of the charged particle beam passing through the first beam path;
The beam transport system (30)
a deflecting electromagnet (33) for deflecting the charged particle beam;
a focusing electromagnet (40) that is installed downstream of the sorting electromagnet and that focuses the charged particle beam that passes through the plurality of beam paths or one of the plurality of beam paths onto the isocenter,
the first beam path is a beam path through which the charged particle beam passes through the deflection electromagnets and is irradiated onto the isocenter when the deflection electromagnets are not excited;
When a charged particle beam is passed through the first beam path, the shield (110) is retracted from the first beam path to allow the charged particle beam to pass through.
[2]
the shield is disposed downstream of the dividing electromagnet and upstream of the converging electromagnet,
The charged particle beam irradiation device according to [1], wherein the first beam path is on a line passing through a deflection origin Q of the deflecting electromagnet and the isocenter.
[3]
A charged particle beam irradiation device,
a beam transport system (30) having a plurality of beam paths for transporting the charged particle beam emitted from the accelerator (20) toward one isocenter (O);
a first shield (110a), a second shield (110b) that moves along a guide rail (55) on which the irradiation nozzle (50) moves, and that is arranged to sandwich the irradiation nozzle (50) in a direction along the guide rail;
The beam transport system includes:
a deflecting electromagnet (33) for deflecting the charged particle beam;
a focusing electromagnet (40) that is installed downstream of the sorting electromagnet and that focuses the charged particle beam passing through the plurality of beam paths onto the isocenter,
the first and second shields are detachably attached to the irradiation nozzle, move in accordance with the movement of the irradiation nozzle, and are fixed when they reach a position on the first beam path of the guide rail;
the first beam path is a beam path through which the charged particle beam passes through the deflecting electromagnet and the focusing electromagnet and is irradiated onto the isocenter when the deflecting electromagnet is not excited.
[4]
the deflecting electromagnet deflects the charged particle beam at a deflection angle φ of 1 degree or more at a deflection starting point Q;
the focusing electromagnet includes a pair of coils arranged on either side of a path of the charged particle beam;
The coil pair is configured to generate an effective magnetic field region in which the magnetic field is oriented in a direction (Z axis) perpendicular to the traveling direction (X axis) of the charged particle beam when a current is input thereto, and the axis perpendicular to the X axis and the Z axis is defined as the Y axis,
In the XY plane,
the charged particle beam is deflected at a deflection angle φ with respect to the X-axis at the deflection origin Q and enters the effective magnetic field region, is deflected by the effective magnetic field region, and is irradiated onto the isocenter at an irradiation angle θ with respect to the X-axis;
An arbitrary point P2 on the boundary of the effective magnetic field region on the exit side of the charged particle beam is located at an equal distance _r1 from the isocenter,
Point P1 on the boundary of the effective magnetic field region on the incident side of the charged particle beam and point P2 are on an arc of radius _r2 and central angle (θ+φ),
When the distance between the deflection origin Q and the isocenter is L, the distance R between the deflection origin Q and the point P1 is expressed by the following relational expression (4):
The charged particle beam irradiation device according to any one of [1] to [3], which satisfies the above.
[5]
an accelerator that generates a charged particle beam;
and a charged particle beam irradiation device according to any one of [1] to [4], which irradiates the isocenter with a charged particle beam generated by the accelerator.

1 is a schematic configuration diagram of a charged particle beam irradiation device according to first and second embodiments of the present invention; 1 is a schematic configuration diagram of a charged particle beam irradiation device according to a first embodiment. FIG. 1 is an explanatory diagram relating to the prior art. 1 is a schematic configuration diagram of a charged particle beam irradiation device according to a first embodiment. 1 is a schematic configuration diagram of a charged particle beam irradiation device according to a first embodiment. FIG. 10 is a schematic configuration diagram of a converging electromagnet according to a second embodiment. 10A and 10B are diagrams for explaining the formation of an effective magnetic field region according to the second embodiment. FIG. 10 is a schematic configuration diagram of a shielding mechanism according to a second embodiment. 10A and 10B are diagrams for explaining the movement of a shield according to the second embodiment. 10 is a flowchart of irradiation control of a charged particle beam irradiation apparatus according to a second embodiment. FIG. 10 is a schematic configuration diagram of a charged particle beam irradiation device according to a third embodiment.

Figure 1 is a schematic diagram of a charged particle beam irradiation system 10 according to the present invention. Figure 1(a) is a diagram of a first embodiment of the present invention, which is a charged particle beam irradiation system in which there are multiple independent beam paths that irradiate a charged particle beam to a single isocenter O within an area in which the beam travels downstream from the deflection origin Q. Figure 1(b) is a diagram of a second embodiment of the present invention, which is a charged particle beam irradiation system in which there are multiple continuous beam paths that irradiate a charged particle beam to a single isocenter O within an area in which the beam travels downstream from the deflection origin Q.

A charged particle beam irradiation device 10 according to one embodiment of the present invention includes a beam transport system 30 having multiple beam paths that transport a charged particle beam emitted from an accelerator 20 toward an isocenter O, and a shield 110 of a shielding mechanism 100 that is disposed on a first beam path among the multiple beam paths of the beam transport system 30 and blocks (shields) the charged particle beam from traveling through the first beam path. When it is desired to pass the charged particle beam through the first beam path, the shield 110 moves (retracts) from the first beam path to allow the charged particle beam to pass through. The first beam path is a beam path along which the charged particle beam passes through the distribution electromagnet 33 (or the distribution electromagnet 33 and the focusing electromagnet 40) and is irradiated at the isocenter O when the distribution electromagnet 33 is not excited. In other words, the first beam path is on a line passing through the deflection origin Q of the distribution electromagnet 33 and the isocenter O.

The charged particle beam irradiation device 10 further includes a focusing electromagnet 40, an irradiation nozzle 50, and a control device 60. Furthermore, a charged particle beam therapy system according to one embodiment of the present invention includes an accelerator 20 and a charged particle beam irradiation device 10.

The accelerator 20 is a device that generates a charged particle beam, and is, for example, a synchrotron, cyclotron, or linear accelerator. The charged particle beam generated by the accelerator 20 is focused at the isocenter O via the beam transport system 30.

The beam transport system 30 includes a deflecting electromagnet 33 that deflects the charged particle beam, and a focusing electromagnet 40 that is installed downstream of the deflecting electromagnet 33 and focuses the charged particle beam at the isocenter O through one of multiple beam paths. The beam transport system 30 may also include one or more charged particle beam adjustment means 31, a vacuum duct 32, a fan-shaped vacuum duct 34, and an irradiation nozzle 50. All beam paths pass through the vacuum regions in the vacuum duct 32, deflecting electromagnet 33, and focusing electromagnet 40 to reach the isocenter O, which is in the atmosphere of the treatment room.

The control device 60 is composed of an irradiation control unit 62, a shield drive control unit 64, and a shield position detection unit 66. The control device 60 controls devices related to irradiation in accordance with irradiation information sent from an irradiation computer (not shown). The shield drive control unit 64 and the shield position detection unit 66 move the shield 110 to a predetermined position, and the control device 60 monitors the position of the shield 110 and controls the emission of the charged particle beam.

A first embodiment of the present invention will be described. Figure 2A is a schematic diagram of a particle beam therapy facility with two treatment rooms. Each treatment room has multiple independent beam paths that originate from a distribution electromagnet 33 (33A, 33B in the figure) and converge at a single isocenter O (O-A, O-B in the figure) within the treatment room. Note that in Figures 1 and 2A-C, the numbers in parentheses following the symbols are as follows: (0A) means zero amperes, (0) is assigned to elements such as electromagnets used when irradiating a charged particle beam from the 0-degree direction, (90) is assigned to elements such as electromagnets used when irradiating a charged particle beam from the 90-degree direction, and (45) is assigned to elements such as electromagnets used when irradiating a charged particle beam from the 45-degree direction.

The charged particle beam extracted from the accelerator 20 and transported is divided into two paths by the distribution magnets 33 (33A and 33B in the figure) at the deflection origin Q (Q-A and Q-B in the figure), and is then irradiated at the intended irradiation angle by the focusing magnet 40. That is, the beam is divided into irradiation paths at 0, 45, and 90 degrees relative to the beam axis of travel at the deflection origin Q (Q-A and Q-B in the figure). For example, if a 45-degree irradiation angle is selected in treatment room B, the excitation current values and other settings for the distribution magnets 33B and focusing magnets 40B (45) are changed in advance. Once all settings are changed, charged particle beam irradiation begins. At this time, the beam path indicated by the thick arrows in the beam transport system 30 in Figure 2A is the set path 220 (intended irradiation path). In this case, treatment room A is not selected, so it is not included in the irradiation path.

Using Figure 2B, we will explain the problem that occurs when the deflection electromagnet 33 unintentionally malfunctions when the shield 110 is not used. For example, even if an irradiation angle of 45 degrees or 90 degrees is selected, that is, even if an excitation current other than 0 A (zero amperes) is specified for the deflection electromagnet 33B, if the excitation current for the deflection electromagnet 33B unintentionally becomes 0 A, the charged particle beam entering the deflection electromagnet 33B will not be deflected by the deflection electromagnet 33B and will travel along an irradiation path in the 0-degree direction. In this case, the charged particle beam will travel along the first beam path 210 indicated by the thick arrow line of the beam transport system 30 in Figure 2B, resulting in unintended irradiation of the isocenter O-B.

When the set path 220 is different from the first beam path 210, the condition for the charged particle beam to be emitted toward the isocenter O is that a shield 110 is placed in the first beam path 210. On the other hand, when the set path 220 is the same as the first beam path 210, the condition is that the beam path is opened, i.e., the shield 110 is retracted from the first beam path 210. The position of the shield 110 is monitored by the control device 60. For example, in the example shown in Figure 2C, even if an irradiation angle of 45 degrees is selected in treatment room B but the excitation current of the distribution electromagnet 33B is unintentionally set to 0 A (zero amperes), the shield 110B will block the charged particle beam traveling along the first beam path 210 and prevent it from reaching the isocenter O-B. Note that because treatment room A is not selected, the position of the shield 110A may or may not be included in the irradiation conditions for treatment room B.

When the irradiation angle is selected to be 0 degrees, the set path 220 (intended irradiation path) is the same as the first beam path 210. In this case, as shown in Fig. 2D, the shield 110B can be retracted from the set path 220 (first beam path 210), thereby enabling irradiation to the isocenter O-B.

A second embodiment of the present invention will now be described. The beam transport system 30 of the charged particle beam irradiation system 10 has multiple continuous beam paths that start at the deflection magnet 33 and converge at a single isocenter O within the treatment room. The desired irradiation angle can be selected by various combinations of the excitation current values of the power supplies for at least two bending electromagnets, the deflection magnet 33 and the focusing electromagnet 40. Figure 3 is a schematic diagram of the deflection magnet 33 and the focusing electromagnet 40 in the second embodiment.

The beam transport system 30 includes multiple beam paths generated by the deflection electromagnet 33 and the focusing electromagnet 40. As described below, the multiple beam paths vary depending on the deflection angle φ of the charged particle beam generated by the deflection electromagnet 33 and the irradiation angle θ of the charged particle beam generated by the focusing electromagnet 40.

Of the multiple beam paths, the first beam path 210 is the beam path along which the charged particle beam naturally travels toward the isocenter O when the distribution electromagnet 33 is unintentionally de-energized. More specifically, the first beam path 210 is the beam path along which the charged particle beam passes through the distribution electromagnet 33 and the focusing electromagnet 40 and is irradiated onto the isocenter O when the distribution electromagnet 33 is not energized (not functioning). In FIG. 4 , the first beam path 210 is the beam path when the distribution electromagnet 33 is not energized and the charged particle beam travels at φ = 0 degrees and θ = 0 degrees, despite the settings of φ ≠ 0 degrees and θ ≠ 0 degrees. Furthermore, the set path 220 for φ = 0 degrees and θ = 0 degrees is the same beam path as the first path 210 when φ ≠ 0 degrees and θ ≠ 0 degrees.

The condition for the charged particle beam to be emitted from the accelerator 20 through the set path 220 toward the isocenter O is that a shield be placed in the first beam path 210. When irradiation with φ ≠ 0 degrees and θ ≠ 0 degrees is selected, the shield 110 is always placed in the first beam path 210 so as to block the beam. On the other hand, when irradiation with φ = 0 degrees and θ = 0 degrees is selected, the set path 220 is the same as the first beam path 210, so the shield 110 is retracted from the set path 220 (first beam path 210) to allow the charged particle beam to proceed. At this time, the position of the shield 110 is monitored by the control device 60. Note that if the shield 110 moves out of its predetermined position, the status of the shield 110 becomes indeterminate, and the beam is immediately blocked.

The accelerator 20, charged particle beam adjusting means 31, and deflecting electromagnet 33 are connected by a vacuum duct 32, and the deflecting electromagnet 33 and focusing electromagnet 40 are connected by a fan-shaped vacuum duct 34 shown in Figure 1. By making the shape of the fan-shaped vacuum duct 34 fan-shaped in the XY plane, even charged particle beams deflected at a deflection angle φ of 1 degree or more, 5 degrees or more, or 10 degrees or more can pass through the vacuum duct, making it more compact than a rectangular duct and reducing installation space.

The charged particle beam is generated in the upstream accelerator 20, travels through vacuum ducts 32 and 34 to avoid (or reduce) attenuation, and is guided to the focusing electromagnet 33 and focusing electromagnet 40 while being adjusted by the charged particle beam adjustment means 31.

The charged particle beam adjustment means 31 uses, as appropriate depending on the specifications, a beam slit for adjusting the beam shape and/or dose of the charged particle beam, an electromagnet for adjusting the direction of travel of the charged particle beam, a quadrupole electromagnet for adjusting the beam shape of the charged particle beam, and a steering electromagnet for fine-tuning the beam position of the charged particle beam.

The multiple beam paths of the beam transport system 30 vary depending on the deflection angle φ of the deflecting electromagnet 33 and the illumination angle θ of the focusing electromagnet 40. The optical elements that the charged particle beam is subjected to also change depending on the deflection angle φ and illumination angle θ, and the beam shape of the charged particle beam at the isocenter O may vary depending on the deflection angle φ and illumination angle θ. To address this variation, for example, the charged particle beam adjustment means 31, which is provided upstream of the focusing electromagnet 40, may be adjusted for each deflection angle φ and illumination angle θ so that the beam shape of the charged particle beam at the isocenter O is appropriate.

The deflecting electromagnet 33 is configured to continuously deflect the charged particle beam at a deflection angle φ and emit the charged particle beam to the focusing electromagnet 40. The focusing electromagnet 40 is also configured to continuously change the irradiation angle θ of the charged particle beam toward the isocenter O. The contents of prior patents by the present applicant (Japanese Patent Nos. 6,364,141, 6,387,476, and 6,734,610) are incorporated herein by reference. An example of the deflecting electromagnet 33 and focusing electromagnet 40 is described below.

The irradiation nozzle 50 is located inside the treatment room where treatment using the charged particle beam is performed, and moves continuously along a guide rail 55 (Figure 8) that follows the shape (boundary shape) of the exit side of the effective magnetic field region generated by the focusing electromagnet 40 in the XY plane. The charged particle beam traveling from the exit side of the effective magnetic field region toward the isocenter O passes through the irradiation nozzle 50, and the irradiation nozzle 50 fine-tunes the direction, shape, energy, etc. of the charged particle beam.

The irradiation nozzle 50 is equipped with a scanning electromagnet (not shown), a beam monitor 51, and an energy modulation means (not shown). The scanning electromagnet adjusts the amount and direction of the current flowing to fine-tune the direction of the charged particle beam emitted from the irradiation nozzle 50, allowing the charged particle beam to be scanned within a relatively narrow range. The beam monitor 51 monitors the charged particle beam and measures the dose monitor and beam position and flatness. The energy modulation means adjusts the energy of the charged particle beam to adjust the depth to which the charged particle beam reaches within the patient. The energy modulation means is, for example, a range modulator, a scatterer, a ridge filter, a patient collimator, a patient bolus, an applicator, or a combination thereof.

Figure 3(a) is a schematic diagram of the focusing electromagnet 40. It also depicts multiple beam paths that differ for each deflection angle φ and convergence angle θ. Here, the X-axis represents the direction of travel of the charged particle beam, the Z-axis represents the direction of the magnetic field generated by the focusing electromagnet 40, and the Y-axis represents the direction perpendicular to the X-axis and Z-axis. The focusing electromagnet 40 is configured to converge the charged particle beam, which is incident on the XY plane from a wide range of deflection angles φ relative to the X-axis, onto the isocenter O. Note that the irradiation nozzle 50 is omitted in Figure 4, and for simplicity, the isocenter O is taken as the origin of the XYZ space, with the upstream side (accelerator side) being the positive X-axis.

The deflection angle φ ranges from greater than -90 degrees to less than +90 degrees, and the positive (+Y-axis) deflection angle range and the negative (-Y-axis) deflection angle range may be different (asymmetric). For example, the maximum deflection angle on the positive side (φ = φMAX) may be 10 degrees, 15 degrees, 20 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees, 45 degrees, 50 degrees, 60 degrees, 70 degrees, 80 degrees, or 85 degrees, and the maximum deflection angle on the negative side (φ = -φMAX) may be -10 degrees, -15 degrees, -20 degrees, -25 degrees, -30 degrees, -35 degrees, -40 degrees, -45 degrees, -50 degrees, -60 degrees, -70 degrees, -80 degrees, or -85 degrees.

The focusing electromagnet 40 comprises one or more coil pairs, which generate a uniform magnetic field (effective magnetic field regions 41a, 41b) oriented in a direction perpendicular to the direction of travel of the charged particle beam and the direction of spread of the deflection angle φ of the charged particle beam (the Z-axis direction in the figure), and are arranged on either side of the path of the charged particle beam. The effective magnetic field region generated by one coil pair of the focusing electromagnet 40 has a crescent shape in the XY plane as shown in Figure 3(a), and details of this will be described later. Note that the gap between opposing coil pairs through which the charged particle beam passes (the distance in the Z-axis direction) is sufficiently small compared to the range of spread of the charged particle beam in the XY plane, so the spread of the charged particle beam in the Z-axis direction will not be considered here.

Figure 3(b) is a cross-sectional view of the focusing electromagnet 40 taken along line A-A. The focusing electromagnet 40 preferably comprises at least two coil pairs 44a, 44b. Magnetic poles 45a, 45b are incorporated within the coils 44a, 44b, respectively, and a yoke 46 is connected to the magnetic poles 45a, 45b. A power supply unit (electromagnet control unit 122, described below) is connected to the focusing electromagnet 40, and when a current (excitation current) is supplied from the power supply unit to the coil pairs 44a, 44b, the focusing electromagnet 40 is excited and effective magnetic field regions 41a, 41b (collectively referred to as effective magnetic field region 41) are formed.

The range of effective magnetic field region 41a and the range of effective magnetic field region 41b 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 41a and 41b can be formed accordingly asymmetrically, thereby reducing the amount of unused effective magnetic field region.

The deflection angle φ of the charged particle beam deflected by the deflection electromagnet 33 and incident on the focusing electromagnet 40 ranges from the maximum positive deflection angle (φ = φmax) to the maximum negative deflection angle (φ = -φmax). The maximum positive deflection angle φmax is an angle between 10 degrees and 90 degrees, and the maximum negative deflection angle -φmax is an angle between -90 degrees and -10 degrees. The deflection angle φ and the irradiation angle θ, described below, are the angles of the path of the charged particle beam relative to the X-axis on the XY plane.

A charged particle beam incident within the positive deflection angle range (φ=greater than 0 to φmax) is deflected by the effective magnetic field region 41a of the first coil pair 44a, passes through the irradiation nozzle 50, and is irradiated onto the isocenter O. A charged particle beam incident within the negative deflection angle range (φ=less than 0 to -φmax) is deflected by the effective magnetic field region 41b of the second coil pair 44b, passes through the irradiation nozzle 50, and is irradiated onto the isocenter O. The magnetic fields of the effective magnetic field region 41a and the effective magnetic field region 41b are oriented in opposite directions. A charged particle beam incident on the focusing electromagnet 40 from the deflection electromagnet 33 at a deflection angle φ=0 passes through either or both of the effective magnetic field regions 41a and 41b, and is converged onto the isocenter O via the irradiation nozzle 50.

The deflection angle φ of the charged particle beam incident on the focusing electromagnet 40 is controlled by the deflection electromagnet 33. The deflection electromagnet 33 generates a magnetic field oriented in a direction (Z-axis in the figure) perpendicular to the direction of propagation (X-axis in the figure) of the charged particle beam supplied from the 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 (neither of which are shown). By controlling the strength and direction (Z-axis direction) of the magnetic field, the deflection electromagnet 33 deflects the charged particle beam in the XY plane, and emits the charged particle beam deflected at the deflection angle φ at the deflection origin Q to the focusing electromagnet 40. Here, the deflection origin Q and the isocenter O are on the X-axis.

Referring to Figure 4, the calculation formula for forming the effective magnetic field region 41a of the focusing electromagnet 40 will be described. Note that in this embodiment, 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. We will now explain the effective magnetic field region 41a of the focusing electromagnet 40, but the same applies to the effective magnetic field region 41b, so a description will be omitted.

First, the boundary of the effective magnetic field region 41a on the exit side 43 of the focusing electromagnet 40 for the charged particle beam is determined to be a range at an equal distance _r1 from the isocenter O. Next, the boundary of the effective magnetic field region 41a on the entrance side 42 of the focusing electromagnet 40 for the charged particle beam is determined based on relational expressions (1) to (5) described below so that the incident charged particle beam is deflected by a deflection angle φ at an imaginary deflection origin Q located at a predetermined distance L from the isocenter O, and converges at the isocenter O. Here, the imaginary deflection origin Q is a point at the center of the deflecting electromagnet 33, where it is assumed that the charged particle beam receives a kick of the deflection angle φ over an extremely short distance.

The charged particle beam transported at a deflection angle φ enters at an arbitrary point P1 on the boundary of the effective magnetic field region 41a on the entrance side 42, performs a circular motion with a radius of curvature _r2 within the effective magnetic field region 41a (the central angle at this time is (φ+θ)), exits at a point P2 on the boundary of the effective magnetic field region 41a on the exit side 43, 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 (φ+θ).

Assume an XY coordinate system 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 exit side 43 and isocenter O is defined as the irradiation angle θ, the coordinates (x, y) of point P1 on the entrance side 42, 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).

Here, a magnetic field with a uniform magnetic flux density B is generated in the effective magnetic field region 41 a, 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).

Based on the above relational expressions (1) to (5), the shape and arrangement of the coil pair 44a and the magnetic pole 45a of the converging electromagnet 40 can be adjusted, and the current flowing through the coil pair 44a can be adjusted to adjust the shape of the boundary of the effective magnetic field region 41a. That is, the boundary is determined so that the distance between any point P2 on the boundary of the effective magnetic field region 41a on the exit side 43 and the isocenter O is equal to _r1 , the magnetic flux density B of the effective magnetic field region 41a is adjusted to determine _r2 from expression (5), and the boundary of the effective magnetic field region 41a on the entrance side 42 is determined so that the distance R between point P1 on the boundary of the effective magnetic field region 41a on the entrance side 42 and the deflection starting point Q satisfies the relationship of expression (4). The maximum value of φ in expression (3) is the maximum deflection angle φmax. Although not limited to this, it is preferable to adjust the positions of the deflection starting point Q, the focusing electromagnet 40, and the isocenter O so that the charged particle beam passing through the deflection starting point Q converges at the isocenter O without being deflected by the focusing electromagnet 40, as this makes the device configuration simpler.

The boundary between the effective magnetic field regions 41a, 41b of the focusing electromagnet 40 determined as described above is an ideal shape for focusing the charged particle beam at the isocenter O. Even if there is deviation from this ideal shape or non-uniformity in the magnetic field distribution, the excitation amount (magnetic flux density B) of the focusing electromagnet 40 can be fine-tuned in advance for each deflection angle φ, the information stored in a power supply unit (e.g., the irradiation control unit 121), and the deflection angle φ and the amount of current in the focusing electromagnet 40 can be controlled so as to be linked, thereby deflecting the charged particle beam to the isocenter O. Furthermore, if the non-uniformity in the magnetic field distribution can be predicted in advance, the trajectory of the charged particle beam can be fine-tuned by correcting the shape and arrangement of the coil pairs 44a, 44b and magnetic poles 45a, 45b of the focusing electromagnet 40.

The control device 60 is a computer equipped with an arithmetic processing unit and a memory unit, and includes an irradiation control unit 62, a shield drive control unit 64, and a shield position detection unit 66 as functional units realized through the cooperation of hardware and software. The irradiation control unit 62 controls the accelerator 20 and each element of the beam transport system 30 (charged particle beam adjustment means 31, distribution electromagnet 33, focusing electromagnet 40, and irradiation nozzle 50). The shield drive control unit 64 controls the movement of the shield 110 of the shielding mechanism 100, and the shield position detection unit 66 determines the position of the shield 110. The irradiation control unit 62, shield drive control unit 64, and shield position detection unit 66 may be configured as the same computer or as separate computers.

Figure 5 is a schematic diagram of the shielding mechanism 100. The shielding mechanism 100 includes a shield 110 that blocks the progression of the charged particle beam, a shaft 112 connected to the shield 110, a fixed end 113 with an opening through which the shaft 112 passes, a biasing member 114 connected to the fixed member 113 at one end and to a movable end 115 at the other end, and a drive mechanism 117 that drives the shaft 116 connected to the movable end 115.

The shield 110 of the shielding mechanism 100 is placed within the vacuum region of the beam transport system 30. For example, the shield 110 is placed within the fan-shaped vacuum duct 34.

The shield 110 is made of a material capable of blocking a charged particle beam with the maximum energy required for treatment, and is shaped to adequately block the spread of the charged particle beam in the YZ plane. For example, the energy of the charged particle beam is sufficient to penetrate to a tumor deep within the patient's body (equivalent to a water thickness of approximately 30 cm). This is approximately 230 MeV for proton beams and 430 MeV/u for carbon ions.

The material of the shield 110 is preferably one that can reduce deterioration of the vacuum level in the vacuum region in which the shield 110 is located (e.g., the sector-shaped vacuum duct 34) even when irradiated with a charged particle beam, and that can reduce the impact of radiation exposure on the patient from neutrons, gamma rays, and secondary charged particles generated by nuclear reactions between the charged particle beam and the shield 110. If the focusing electromagnet 40 is a superconducting electromagnet, the vacuum vessel of the focusing electromagnet 40 is maintained at an extremely low temperature of around several Kelvin (K). Therefore, the shield 110 should preferably be made of a material that has an extremely low rate of gas release from its surface and a low emissivity (e.g., a material that does not contain oxygen). Examples of materials for the shield 110 include oxygen-free copper and SUS, which have a high electron density (large water equivalent thickness).

The shape of the shield 110 is preferably larger than the beam size, taking into consideration the beam size of the charged particle beam, trajectory errors on the beam path, beam energy, etc. On the other hand, since the shield 110 will always be positioned on the first beam path except when a charged particle beam is irradiated on the first beam path, it should be large enough not to interfere with charged particle beams passing through other beam paths.

The biasing member 114, which may be, for example, a bellows or magnetic seal, biases the shaft 112 so that the shield 110 is positioned on the first beam path 210 when no external force is being applied to the shield 110 (Figure 6(a)). The drive mechanism 117 includes, for example, an air compressor and a compression cylinder. In response to a control signal from the shield drive control unit 64, the drive mechanism 117 drives (pulls) the shaft 116, moving the movable end 115 to stretch the biasing member 114 and move the shaft 112, thereby moving the shield 110. When the shield drive control unit 64 removes the stress applied by the drive mechanism 117, the shield 110 is moved by the biasing member 114 and returns to its insertion position on the first beam path 210.

The shield position detection unit 66 receives a drive signal from the shield drive control unit 64 and/or a signal from a sensor attached to the shield 110 to determine whether the shield 110 is positioned on the first beam path 210. The sensor may be either contact or non-contact. As an example of a mechanism for monitoring the insertion/retraction position, the insertion/retraction position of the shield 110 is detected by a limit switch (not shown). The switch is provided on a rail (not shown) that guides the extension/retraction of the biasing member 114, and is positioned at the position where the movable end 115 stops (insertion position (IN) on the first beam path 210, retraction position (OUT) from the first beam path 210). The movable end 115 is equipped with a position detection bar (not shown), which detects the position of the shield 110 by contacting the IN switch or OUT switch. If the position detection bar is not in contact with either switch, the state becomes indeterminate.

The movement of the shield 110 will be explained using Figure 6. Figure 6(a) depicts a charged particle beam that passes through a set path 220 of the multiple beam paths of the beam transport system 30, where φ ≠ 0 degrees and θ ≠ 0 degrees, and is irradiated at the isocenter O. At this time, the distribution electromagnet 33 and focusing electromagnet 40 (effective magnetic field region 41a) are excited, and the shield 110 is inserted onto the first beam path 210 without being subjected to stress by the drive mechanism 117.

Figure 6(c) illustrates a charged particle beam that passes through a set path 220 of φ = 0 degrees and θ = 0 degrees, one of the multiple beam paths of the beam transport system 30, and is irradiated to the isocenter O. At this time, the deflection electromagnet 33 and the focusing electromagnet 40 (effective magnetic field region 41a) are at 0A, and the set path 220 is the beam path that passes through the deflection electromagnet 33 (more specifically, the deflection origin Q) and the focusing electromagnet 40 and is irradiated to the isocenter O. In this case, the shield 110 is subjected to stress by the driving mechanism 117 and retracts from the set path 220 (first beam path 210) so that the charged particle beam can pass through the set path 220 (first beam path 210).

When a charged particle beam is irradiated to the isocenter O through a beam path other than the first beam path 210, that is, when the charged particle beam is irradiated through the set path 220 where φ ≠ 0 degrees and θ ≠ 0, the shield position detection unit 66 determines that the shield 110 is inserted on the first beam path 210, and the irradiation control unit 62, based on the determination result by the shield position detection unit 66, irradiates the charged particle beam through a beam path other than the first beam path 210. On the other hand, when the charged particle beam is irradiated to the isocenter O through the first beam path 210, that is, when the charged particle beam is irradiated through the set path 220 where φ = 0 degrees and θ = 0, the shield position detection unit 66 determines that the shield 110 has moved to a position retracted from the set path 220 (first beam path), and the irradiation control unit 62 receives the determination result from the shield position detection unit 66 and irradiates the charged particle beam through the set path 220 (first beam path).

In this way, even if the deflection electromagnet 33 is not excited due to a malfunction of the control device 60 or the occurrence of an unstable control state, and the charged particle beam is not deflected in the intended direction at the deflection starting point Q (deflection angle φ = 0 degrees), the shield 110 prevents the charged particle beam from being irradiated onto the isocenter O through the first beam path 210 (Figure 6(b)).

In addition, not only when the deflection electromagnet 33 is not unintentionally excited (deflection angle φ = 0 degrees), but also when the deflection by the deflection electromagnet 33 does not reach the intended angle (irradiation angle) (deflection angle φ < irradiation angle), the insertion position of the shield 110 may be adjusted to block the charged particle beam passing through that beam path. Also, the shielding mechanism 100 may be configured to include multiple shields 110, and beam paths with an empirical high probability of unintended operation of one or both of the deflection electromagnet 33 and the focusing electromagnet 40 may be investigated, and a shield 110 may be placed on each of these beam paths.

Figure 7 is a flowchart of the charged particle beam irradiation control. The irradiation control unit 62 receives irradiation information such as the energy of the charged particle beam, the excitation current value of the electromagnet power supply that specifies the set path 220 of the charged particle beam, the irradiation pattern, the deflection angle φ, and the irradiation angle θ from another computer (not shown) (step S1).

The irradiation control unit 62 transmits excitation current setting values to the power supplies (not shown) of the electromagnet group including the distribution electromagnet 33 and the focusing electromagnet 40 so that the charged particle beam passes through the specified set path 220 and is irradiated onto the isocenter O (step S2). The irradiation control unit 62 moves the irradiation nozzle 50 so that the charged particle beam passes through the irradiation nozzle 50 and is irradiated onto the isocenter O (step S3).

The irradiation control unit 62 determines whether the specified set path 220 is a beam path that travels at φ = 0 degrees and θ = 0 degrees, i.e., the first beam path 210 (step S4).

If the specified set path 220 is the first beam path 210 (Yes in step S4), that is, if the excitation current of the polarizing electromagnet 33 is set to 0 A, the irradiation control unit 62 sends a command to the shield drive control unit 64 to retract the shield 110 from the set path 220 (first beam path 210). In response to this command, the shield drive control unit 64 retracts the shield 110 from the set path 220 (first beam path 210) (step S5). Note that if the shield 110 is already in a position retracted from the set path 220 (first beam path 210), the shield 110 does not move. The shield position detection unit 66 detects that the shield 110 is in the retracted position and sends this information to the irradiation control unit 62.

If the specified set path 220 is not the first beam path 210 (No in step S4), the irradiation control unit 62 sends a command to the shield drive control unit 64 to insert the shield 110 onto the first beam path 210, and in response, the shield drive control unit 64 inserts the shield 110 onto the first beam path 210 (step S6). Note that if the shield 110 is already inserted onto the first beam path 210, the shield 110 does not move. The shield position detection unit 66 detects that the shield 110 is located on the first beam path 210 and sends this information to the irradiation control unit 62.

The irradiation control unit 62 determines that the shield 110 is in the specified position based on information from the shield position detection unit 66. Similarly, when it determines that the settings for all devices involved in irradiation have been completed, the irradiation control unit 62 sends a charged particle beam extraction request to the accelerator control unit 63. This signal triggers the accelerator control unit 63 to issue a charged particle beam extraction permission signal, causing the charged particle beam to be extracted and irradiating the isocenter O with the charged particle beam (step S7).

During irradiation, the shield position detection unit 66 transmits the position of the irradiator 110 to the irradiation control unit 62 at regular intervals, and the irradiation control unit 62 monitors this position (step S8). If the position of the shield 110 remains unchanged, irradiation continues (Yes in step S8). Irradiation is completed when the dose irradiated based on the irradiation information is reached (step 9). For example, if the shield 110 moves from its retracted position when the set path 220 is the first beam path 210 (φ = 0 degrees and θ = 0 degrees), or if the shield 110 moves from its inserted position when the set path 220 is not the first beam path 210 (φ ≠ 0 degrees and θ ≠ 0 degrees), the shield 110 enters an unstable state (No in step S8). If an unstable state is detected, an interlock control (not shown) is notified, and the accelerator control unit 63 immediately blocks the charged particle beam (step S10).

In the charged particle beam irradiation device 10 of this embodiment, the shield 110 is always positioned on the first beam path except when the charged particle beam passes through the first beam path 210, thereby preventing unintended irradiation of the isocenter O with the charged particle beam through the first beam path. Here, the first beam path 210 is a beam path through which the charged particle beam passes through the distribution electromagnet 33 and/or the focusing electromagnet 40 and is irradiated onto the isocenter O when the distribution electromagnet 33 is not excited. Preferably, the first beam path 210 is a beam path through which the charged particle beam passes through the distribution electromagnet 33 and/or the focusing electromagnet 40 and is irradiated onto the isocenter O when the distribution electromagnet 33 is not excited. Furthermore, the shield 110 can be installed within the vacuum region of the beam transport system 30, thereby reducing the size of the device. If the shield 110 is made of a material that does not contain oxygen (for example, oxygen-free copper), it is possible to reduce the effects of exposure to patients due to the generation of secondary particles (secondary charged particles, neutrons, gamma rays, and/or photons) caused by the nuclear reaction between the shield 110 and the charged particle beam, as well as the deterioration of the degree of vacuum due to gas generation from the shield 110.

A charged particle beam irradiation device 10 according to another embodiment of the present invention includes multiple shields 110 (first shield 110a, second shield 110b), which are not located in the vacuum region of the beam transport system 30 but are mounted movably along guide rails 55 along which the irradiation nozzle 50 moves. The guide rails 55 are arranged to follow the shape of the exit sides of the effective magnetic field regions 41a, 41b of the focusing electromagnet 40, as described in Japanese Patent No. 6,387,476, which is incorporated by reference.

Figure 8 is a schematic diagram of a third embodiment of the charged particle beam irradiation device 10 according to this embodiment. Two shields 110a and 110b are attached to a guide rail 55 along which the irradiation nozzle 50 moves, and are arranged to sandwich the irradiation nozzle 50 in the direction along the guide rail 55. The upper side facing the page is designated as shield 110a, and the lower side is designated as shield 110b.

Shields 110a and 110b are movable along guide rails 55. In this embodiment, shields 110a and 110b are equipped with means for detachably attaching to the irradiation nozzle 50 (e.g., magnets, electromagnets, or detachable engaging means), and shields 110a and 110b also move as the irradiation nozzle 50 moves. However, when shield 110a or shield 110b reaches a position on the first beam path 210 of guide rail 55, it is latched and fixed in that position, and remains in that position. Shields 110a and 110b may also be equipped with a drive device such as a motor, and configured to move autonomously along guide rails 55 under the control of the shield drive control unit 64.

When the charged particle beam is irradiated to the isocenter O through a set path 220 (first beam path 210) with φ = 0 degrees and θ = 0 degrees (Figure 8(a)), the shields 110a and 110b are positioned near the irradiation nozzle 50.

When the charged particle beam is irradiated to the isocenter O via a set path 220 passing through the effective magnetic field region 41a (Figure 8(b)), the shield 110b is positioned and latched onto the first beam path 210, and the shield 110a moves together with the irradiation nozzle 50. When the charged particle beam is irradiated via a beam path passing through the effective magnetic field region 41a, the shield 110b remains fixed onto the first beam path 210.

On the other hand, when the charged particle beam is irradiated to the isocenter O via the set path 220 that passes through the effective magnetic field region 41b (Figure 8(c)), the shield 110a is positioned and latched onto the first beam path 210, and the shield 110b moves together with the irradiation nozzle 50. When the charged particle beam is irradiated via a beam path that passes through the effective magnetic field region 41b, the shield 110a remains fixed onto the first beam path 210.

As in the above embodiment, in this embodiment, even if the deflection electromagnet 33 is unintentionally not excited when a charged particle beam is irradiated onto the isocenter O along a set path 220 (a beam path other than the first beam path 210) where φ=0 degrees and θ=0 degrees, unintentional irradiation of the charged particle beam is prevented because the shield 110a or 110b is always positioned on the first beam path 210.

The dimensions, materials, shapes, relative positions of components, and the like described above may be changed depending on the structure of the device to which the present invention is applied or various conditions. It is not intended to be limited to the specific terms and embodiments used in the description; those skilled in the art will be able to use other equivalent components, and other modifications and variations of the above embodiments are possible without departing from the spirit or scope of the present invention. Furthermore, features described in connection with one embodiment of the present invention may also be used in combination with other embodiments, even if not explicitly stated above.

10 Charged particle beam irradiation device 20 Accelerator 30 Beam transport system 31 Charged particle beam adjustment means 32 Vacuum duct 33 Dividing electromagnet 34 Sector-shaped vacuum duct 40 Converging electromagnet 50 Irradiation nozzle 55 Guide rail 100 Shielding mechanism 110 (110A, 110B) Shields 110a, 110b First and second shields

Claims (5)

A charged particle beam irradiation device,
a beam transport system (30) having a plurality of beam paths for transporting the charged particle beam emitted from the accelerator (20) to one isocenter (O);
a shield (110) disposed on a first beam path among the plurality of beam paths and configured to block travel of the charged particle beam passing through the first beam path;
The beam transport system (30)
a deflecting electromagnet (33) for deflecting the charged particle beam;
a focusing electromagnet (40) that is installed downstream of the sorting electromagnet and that focuses the charged particle beam that passes through the plurality of beam paths or one of the plurality of beam paths onto the isocenter,
the first beam path is a beam path through which the charged particle beam passes through the deflection electromagnets and is irradiated onto the isocenter when the deflection electromagnets are not excited;
When a charged particle beam is passed through the first beam path, the shield (110) is retracted from the first beam path to allow the charged particle beam to pass through. the shield is disposed downstream of the dividing electromagnet and upstream of the converging electromagnet,
2. The charged particle beam irradiation system according to claim 1, wherein the first beam path is on a line passing through a deflection origin Q of the deflecting electromagnet and the isocenter. A charged particle beam irradiation device,
a beam transport system (30) having a plurality of beam paths for transporting the charged particle beam emitted from the accelerator (20) toward one isocenter (O);
a first shield (110a), a second shield (110b) that moves along a guide rail (55) on which the irradiation nozzle (50) moves, and that is arranged to sandwich the irradiation nozzle (50) in a direction along the guide rail;
The beam transport system includes:
a deflecting electromagnet (33) for deflecting the charged particle beam;
a focusing electromagnet (40) that is installed downstream of the sorting electromagnet and that focuses the charged particle beam passing through the plurality of beam paths onto the isocenter,
the first and second shields are detachably attached to the irradiation nozzle, move in accordance with the movement of the irradiation nozzle, and are fixed when they reach a position on the first beam path of the guide rail;
the first beam path is a beam path through which the charged particle beam passes through the deflecting electromagnet and the focusing electromagnet and is irradiated onto the isocenter when the deflecting electromagnet is not excited. the deflecting electromagnet deflects the charged particle beam at a deflection angle φ of 1 degree or more at a deflection starting point Q;
the focusing electromagnet includes a pair of coils arranged on either side of a path of the charged particle beam;
The coil pair is configured to generate an effective magnetic field region in which the magnetic field is oriented in a direction (Z axis) perpendicular to the traveling direction (X axis) of the charged particle beam when a current is input thereto, and the axis perpendicular to the X axis and the Z axis is defined as the Y axis,
In the XY plane,
the charged particle beam is deflected at a deflection angle φ with respect to the X-axis at the deflection origin Q and enters the effective magnetic field region, is deflected by the effective magnetic field region, and is irradiated onto the isocenter at an irradiation angle θ with respect to the X-axis;
An arbitrary point P2 on the boundary of the effective magnetic field region on the exit side of the charged particle beam is located at an equal distance _r1 from the isocenter,
Point P1 on the boundary of the effective magnetic field region on the incident side of the charged particle beam and point P2 are on an arc of radius _r2 and central angle (θ+φ),
When the distance between the deflection origin Q and the isocenter is L, the distance R between the deflection origin Q and the point P1 is expressed by the following relational expression (4):
4. The charged particle beam irradiation device according to claim 1, wherein the above condition is satisfied. an accelerator that generates a charged particle beam;
and a charged particle beam irradiation device according to any one of claims 1 to 4, which irradiates the isocenter with the charged particle beam generated by the accelerator.