JP5380693B2 - Charged particle beam irradiation apparatus and control method of charged particle beam apparatus - Google Patents

Description

The present invention relates to a charged particle beam irradiation apparatus and a charged particle beam apparatus control method.

  For example, in an accelerator equipped with an internal ion source such as a cyclotron, the irradiation state / non-irradiation state of a beam (charged particle beam) is switched by ON / OFF control of arc discharge of the ion source. Conventionally, as a device for blocking a cyclotron beam, for example, there is a technique described in Patent Document 1. In the beam blocking device described in Patent Document 1, in the internal ion source type cyclotron, the beam is blocked by moving a shutter disposed in the vicinity of the internal ion source on the beam trajectory.

JP 2002-25797 A

  FIG. 8 is a graph showing an example of a beam current when the internal ion source is started by generating an arc discharge. Since the rise of the arc discharge is unstable as shown in FIG. 8, the beam emitted from the accelerator is similarly unstable, and as a result, there is a possibility that an uneven irradiation field is formed.

  Further, in the prior art described in Patent Document 1, since the irradiation state / non-irradiation state of the beam is switched by mechanically opening and closing the shutter, there is a problem that switching at high speed is difficult. there were.

Accordingly, the present invention provides a charged particle beam with speeding switching the irradiation state / non-irradiation state of, stabilizing the charged particle beam irradiation apparatus capable of achieving the charged particle beam emitted and charged particle beam irradiation It aims at providing the control method of an apparatus .

The charged particle beam irradiation apparatus according to the present invention is a charged particle beam irradiation apparatus for irradiating a charged particle beam to the irradiation object, an ion source for generating charged particles, the accelerating electrode to the charged particles generated in the ion source An accelerator that accelerates charged particles by applying an acceleration voltage and emits a charged particle beam, and a control unit that controls the acceleration voltage, the control unit uses the acceleration voltage in the irradiation state of the charged particle beam as a reference acceleration voltage, It is characterized by comprising a set acceleration voltage control means for switching the acceleration voltage to a set acceleration voltage that is larger or smaller than the reference acceleration voltage so that the charged particle beam is not irradiated.

The charged particle beam irradiation apparatus control method according to the present invention generates charged particles with an ion source, accelerates the generated charged particles with an accelerator, emits the charged particle beam, and irradiates the irradiated object with the charged particle beam. A charged particle beam irradiation apparatus control method for generating charged particles by an ion source and a control process for controlling an acceleration voltage applied to the charged particles by an accelerator electrode to accelerate the charged particles. The control process includes a set acceleration for setting the charged particle beam in a non-irradiated state by setting the acceleration voltage in the irradiation state of the charged particle beam as a reference acceleration voltage and switching the acceleration voltage to a set acceleration voltage larger or smaller than the reference acceleration voltage. A voltage control step is provided.

  In this invention, the acceleration voltage in the irradiation state of the charged particle beam is used as a reference acceleration voltage, and the acceleration voltage is switched to a set acceleration voltage that is larger or smaller than the reference acceleration voltage, thereby changing the trajectory of the charged particle beam, The charged particle beam can be made non-irradiated by causing the charged particle beam to collide with the object. In this way, since the non-irradiation state can be achieved simply by switching the acceleration voltage to a larger or smaller value, the switching between the charged particle beam irradiation state / non-irradiation state can be speeded up. Further, irradiation / non-irradiation of charged particles can be switched regardless of ON / OFF control of arc discharge of the ion source, so that the charged particle beam is not affected by instability at the start of arc discharge. Stabilization can be achieved.

  Here, the set acceleration voltage control means preferably controls the set acceleration voltage so that charged particles emitted from the ion source collide with an electrode provided in the accelerator. In this way, the set acceleration voltage is controlled to cause the charged particle beam emitted from the ion source to collide with the electrode, thereby bringing about a non-irradiation state. Thereby, a charged particle beam can be made to collide with the electrode currently arrange | positioned and it can be set as a non-irradiation state.

  Further, it is preferable to generate arc discharge in the ion source after switching to the set acceleration voltage, and to switch the acceleration voltage to the reference acceleration voltage after the occurrence of arc discharge. As a result, the time during which the acceleration voltage is changed to the set acceleration voltage can be shortened. Therefore, it is possible to suppress the temperature drop of the acceleration electrode and stabilize the charged particle beam.

  According to the present invention, it is possible to increase the speed of switching between the irradiation state / non-irradiation state of a charged particle beam while stabilizing the emitted charged particle beam.

It is a perspective view which shows a part of charged particle beam irradiation apparatus which concerns on embodiment of this invention. It is a schematic block diagram of the charged particle beam irradiation apparatus of FIG. It is a schematic block diagram of the cyclotron in FIG. It is a principal part enlarged view of the center vicinity of the cyclotron of FIG. It is a graph which shows the relationship of the acceleration voltage at the time of implementing only switching of an acceleration voltage, an arc voltage, and a beam current. It is a graph which shows the relationship of the acceleration voltage at the time of taking in ON / OFF control of an arc voltage, an arc voltage, and a beam current. It is a figure for demonstrating operation | movement of the charged particle beam irradiation apparatus of FIG. It is a graph which shows the beam current at the time of making a charged particle beam into an irradiation state by carrying out ON / OFF control of arc discharge. It is a graph which shows the relationship between an acceleration voltage and beam current.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same or equivalent elements will be denoted by the same reference numerals, and redundant description will be omitted.

  A charged particle beam irradiation apparatus according to an embodiment of the present invention will be described. FIG. 1 is a perspective view showing a part of a charged particle beam irradiation apparatus according to an embodiment of the present invention, and FIG. 2 is a schematic configuration diagram of the charged particle beam irradiation apparatus of FIG. A charged particle beam irradiation apparatus 1 shown in FIG. 1 is based on a scanning method, is attached to a rotating gantry 12 provided so as to surround a treatment table 11, and can be rotated around the treatment table 11 by the rotating gantry 12. Has been. Although not shown in FIG. 1, the charged particle beam irradiation apparatus 1 includes an accelerator 2 at a position away from the treatment table 11 and the rotating gantry 12.

  As illustrated in FIG. 2, the charged particle beam irradiation apparatus 1 continuously irradiates a charged particle beam R toward a tumor (irradiation object) 14 in the body of a patient 13. Specifically, the charged particle beam irradiation apparatus 1 divides the tumor 14 into a plurality of layers in the depth direction (Z direction), and charges along the irradiation line L (see FIG. 7) in the irradiation field F set in each layer. Continuous irradiation (so-called raster scanning or line scanning) is performed while scanning the particle beam R at the scanning speed V. That is, the charged particle beam irradiation apparatus 1 divides the tumor 14 into a plurality of layers and performs planar scanning on each of these layers in order to form a three-dimensional irradiation field that matches the tumor 14. Thereby, the charged particle beam R is irradiated according to the three-dimensional shape of the tumor 14.

  The charged particle beam R is obtained by accelerating charged particles at a high speed. Examples of the charged particle beam R include a proton beam, a heavy particle (heavy ion) beam, and an electron beam. The irradiation field F is, for example, a region having a maximum size of 200 mm × 200 mm. As shown in FIG. 7, the irradiation field F here has a rectangular outer shape. Note that the shape of the irradiation field F may be various shapes, for example, may be a shape along the shape of the tumor 14.

  The irradiation line L is a planned line (virtual line) for irradiating the charged particle beam R. The irradiation line L here extends in a rectangular wave shape by taking line scanning as an example, and specifically, a plurality of first irradiation lines L1 (L11 to L1n, n) arranged in parallel at a predetermined interval. Is an integer) and a plurality of second irradiation lines L2 connecting one end or the other end of the adjacent first irradiation lines L1.

  Returning to FIG. 2, the charged particle beam irradiation apparatus 1 includes a cyclotron 2, focusing electromagnets 3 a and 3 b, monitors 4 a and 4 b, scanning electromagnets 5 a and 5 b, a fine degrader 8, and a control unit 6.

The cyclotron 2 is a generation source that continuously generates charged particle beams R. The charged particle beam R generated by the cyclotron 2 is transported by the beam transport system 7 to the subsequent focusing electromagnet 3a. The cyclotron 2 is configured to be able to switch the irradiation state (ON) / non-irradiation state (OFF) of the charged particle beam R in response to a command signal output from the control unit 6.

  The converging electromagnets 3a and 3b focus the charged particle beam R to converge. The focusing electromagnets 3a and 3b are arranged on the downstream side of the cyclotron 2 on the irradiation axis of the charged particle beam R (hereinafter simply referred to as “irradiation axis”).

  The monitor 4a monitors the beam position of the charged particle beam R, and the monitor 4b monitors the absolute value of the dose of the charged particle beam R and the dose distribution of the charged particle beam R. The monitor 4a is disposed between the focusing electromagnets 3a and 3b, for example, on the irradiation axis, and the monitor 4b is disposed on the downstream side of the focusing electromagnet 3b, for example, on the irradiation axis.

  The scanning electromagnets 5a and 5b are for scanning the charged particle beam R. Specifically, the irradiation position of the charged particle beam R passing therethrough is moved in the irradiation field by changing the magnetic field according to the applied current. The scanning electromagnet 5a scans the charged particle beam R in the X direction (direction orthogonal to the irradiation axis) of the irradiation field F, and the scanning electromagnet 5b is the Y direction (direction orthogonal to the irradiation axis and the X direction) of the irradiation field F. The charged particle beam R is scanned. These scanning electromagnets 5a and 5b are arranged between the converging electromagnet 3b and the monitor 4b on the irradiation axis. In some cases, the scanning electromagnet 5a scans the charged particle beam R in the Y direction, and the scanning electromagnet 5b scans the charged particle beam R in the X direction.

  The fine degrader 8 is for irradiating each layer of the tumor 14 divided into a plurality of layers in the depth direction with the charged particle beam R. Specifically, the fine degrader 8 changes the energy loss of the charged particle beam R that passes therethrough and adjusts the arrival depth of the charged particle beam R in the body of the patient 13, so that each of the divided layers The arrival depth of the charged particle beam R is adjusted to one layer.

  The control device (control means) 6 is electrically connected to the monitor 4b and the scanning electromagnets 5a and 5b, and scans based on the absolute value and dose distribution of the charged particle beam R monitored by the monitor 4b. The operation of the electromagnets 5a and 5b is controlled. The control device 6 is electrically connected to the cyclotron 2 and controls the operation of the cyclotron 2. The control device 6 controls the acceleration voltage and arc voltage of the cyclotron 3.

  FIG. 3 is a schematic configuration diagram of the cyclotron in FIG. The cyclotron 2 is connected to an ion source (charged particle generation source) 21 that generates ionized particles (charged particles), a pair of acceleration electrodes 23 and 24 that are connected to a high-frequency power source 22 and accelerate charged particles, and both sides of the acceleration electrodes 23 and 24. A plurality of counter electrodes 25 to 28 arranged, and phase slits 34 arranged on both sides of the orbit R1 of charged particles are provided.

  The accelerating electrode 23 has central electrodes 31 and 32 that are arranged at the center of the cyclotron 2 and that define the orbit R1 of the charged particles. The accelerating electrode 24 is disposed in the center of the cyclotron 2 and has a central electrode 33 that defines the orbit R1 of charged particles.

  The charged particles generated in the ion source 21 are accelerated by an acceleration voltage applied by the acceleration electrodes 23 and 24, and are accelerated while circling on the orbit R1 in a normal irradiation state.

  The control device 6 functions as a control unit that controls an acceleration voltage for accelerating the charged particles. The control device 6 controls the irradiation state / non-irradiation state of the charged particle beam R by switching the acceleration voltage.

  The control device 6 sets the acceleration voltage in the irradiation state to the reference acceleration voltage V (H), and switches the acceleration voltage to a set acceleration voltage V (L) that is smaller than the reference acceleration voltage V (H). The irradiation state is assumed. The set acceleration voltage V (L) is preferably a voltage that is about 10-30% lower than the reference acceleration voltage V (H). The lower limit of the set acceleration voltage V (L) is limited by the multi-pacting condition of the acceleration cavity.

  The control device 6 functions as an arc voltage control means for controlling an arc voltage for generating arc discharge in the ion source 21.

  FIG. 5 is a graph showing the relationship between the acceleration voltage, arc voltage, and beam current when only switching of the acceleration voltage is performed. In FIG. 5, the horizontal axis indicates the passage of time, “V1” indicates the acceleration voltage, “V2” indicates the arc voltage, and “I1” indicates the change in the beam current.

  First, at time T1, the control device 6 sets the acceleration voltage V1 to the set acceleration voltage V (L). Subsequently, at time T2, an arc voltage V2 in the ion source 21 is generated. At this time, the charged particles extracted from the ion source 21 move along a trajectory R0 indicated by a solid line in FIG. The charged particles disappear and become non-irradiated.

  Next, at time T3, the acceleration voltage V1 is set to the reference acceleration voltage V (H). At this time, the charged particles extracted from the ion source 21 are moved and accelerated along a trajectory R1 indicated by a broken line in FIG. 4 to be in an irradiation state.

  Subsequently, at time T4, the acceleration voltage V1 is set to the set acceleration voltage V (L). At this time, the charged particles extracted from the ion source 21 move along a trajectory R0 indicated by a solid line in FIG. The charged particles disappear and become non-irradiated.

  FIG. 6 is a graph showing the relationship between the acceleration voltage, arc voltage, and beam current when arc voltage ON / OFF control is taken. In FIG. 6, the horizontal axis indicates the passage of time, “V3” indicates the acceleration voltage, “V4” indicates the arc voltage, and “I2” indicates the change in the beam current.

  First, at time T5, the acceleration voltage V3 is set to the reference acceleration voltage V (H). Subsequently, at time T6, the acceleration voltage V3 is set to the set acceleration voltage V (L). Next, at time T7, the arc voltage V4 is generated to be in a non-irradiation state, and at time T8, the acceleration voltage V3 is set to the reference acceleration voltage V (H). At this time, the charged particles extracted from the ion source 21 move along a trajectory R1 indicated by a broken line in FIG. 4 and are accelerated to be in an irradiated state.

  Subsequently, at time T9, the acceleration voltage V3 is set to the set acceleration voltage V (L). At this time, the charged particles extracted from the ion source 21 move along a trajectory R0 indicated by a solid line in FIG. The charged particles disappear and become non-irradiated.

  Next, at time T10, the arc voltage V4 is turned OFF, and at time T11, the acceleration voltage V3 is set to the reference acceleration voltage V (H).

  Next, operation | movement of the charged particle beam irradiation apparatus 1 demonstrated is demonstrated.

  In the charged particle beam irradiation apparatus 1, the tumor 14 is divided into a plurality of layers in the depth direction, and the charged particle beam R is irradiated toward the irradiation field F set in the one layer. By repeating this for each layer, the charged particle beam R is irradiated along the three-dimensional shape of the tumor 14.

  When irradiating the charged particle beam R, the controller 6 scans the charged particle beam R in parallel along the irradiation line L of the irradiation field F by controlling the scanning electromagnets 5a and 5b.

  Here, when the charged particle beam R is in an irradiation state, the control device 6 generates arc discharge in the ion source 21 and controls the acceleration voltage to the reference acceleration voltage V (H) to accelerate the charged particles. (Control process). Thereby, the accelerated charged particle is irradiated from the cyclotron 2.

  On the other hand, when the charged particle beam R is switched from the irradiation state to the non-irradiation state, the control device 6 changes the acceleration voltage from the reference acceleration voltage V (H) to the set acceleration voltage V (L) (set acceleration voltage control). Process). As a result, as shown in FIG. 4, the charged particles extracted from the ion source 21 travel along the trajectory R0, collide with the center electrode 32, and are not accelerated. Therefore, charged particles are not irradiated from the cyclotron 2.

  When switching the charged particle beam R from the non-irradiation state to the irradiation state, the control device 6 changes the acceleration voltage from the set acceleration voltage V (L) to the reference acceleration voltage V (H).

  As described above, according to the charged particle beam irradiation apparatus 1 of the present embodiment, the acceleration voltage in the charged particle beam irradiation state is set as the reference acceleration voltage, and the acceleration voltage is switched to a set acceleration voltage smaller than the reference acceleration voltage. The irradiation state is assumed. That is, the acceleration voltage is reduced, the trajectory of the charged particle beam is changed, and the charged particle beam is made to collide with the center electrode 32 and disappear. As described above, since the non-irradiation state can be achieved by simply switching the acceleration voltage to a small value, the switching between the irradiation state / non-irradiation state of the charged particle beam can be speeded up. In the charged particle beam irradiation apparatus 1 of the present embodiment, ON / OFF control of the beam current can be executed in 1 ms or less, for example.

  Since the charged particle beam apparatus provided with the charged particle beam irradiation control apparatus of the present invention can perform switching (ON / OFF control) of the irradiation state / non-irradiation state of the charged particle beam at high speed, the treatment for performing scanning irradiation is performed. This is particularly effective in the apparatus. When performing scanning irradiation, for example, it is important to stabilize the beam in 1 ms or less. By switching and stabilizing the beam in 1 ms or less, the uniformity of the beam can be suitably maintained. For example, in irradiation along the first irradiation line L1 in FIG. 7, continuous irradiation of 10 ms or less per line is performed.

  Further, irradiation / non-irradiation of charged particles can be switched regardless of the arc discharge ON / OFF control of the ion source 21. Therefore, at the time of this switching, the influence of instability at the start of the arc discharge may be affected. Absent. Thereby, stabilization of the charged particle beam after switching to the irradiation state of a charged particle beam can be aimed at.

  Moreover, since it is the structure which makes a charged particle beam collide with the center electrode 32 and extinguishes, a charged particle beam can be made into a non-irradiation state by utilizing the center electrode 32 set conventionally.

  Further, since the non-irradiation state can be achieved without turning off the acceleration voltage, the temperature of the acceleration electrode does not drop significantly.

  Here, in order to further suppress the temperature decrease of the acceleration electrode, the ion source arc is turned off and the acceleration voltage is set to the reference acceleration voltage V (H) until just before the charged particle beam is irradiated. Next, after the acceleration voltage is switched from the reference acceleration voltage V (H) to the set acceleration voltage V (L), arc discharge in the ion source 21 is generated. Next, after the arc discharge is stabilized, the acceleration voltage is switched from the set acceleration voltage V (L) to the reference acceleration voltage V (H). Thus, by shortening the time for controlling the acceleration voltage to the set acceleration voltage V (L), the temperature drop of the acceleration electrode can be minimized, and the charged particle beam can be stabilized.

FIG. 9 is a graph showing the relationship between the acceleration voltage and the beam current. In FIG. 9, the horizontal axis represents the acceleration voltage, and the vertical axis represents the beam current. In the figure, “V _pmax ” indicates the maximum voltage for the multi-pacting condition of the acceleration cavity, “V (L)” is the set acceleration voltage V (L), and “V (H)” is the reference acceleration. The voltage is V (H). “V (H) _min ” is an acceleration voltage V (H) _min at which a beam current starts to occur. The acceleration voltage V (H) _{min at} which the beam current starts to occur is different for each cyclotron, and there is no simple regularity. The set acceleration voltage V (L) only needs to be set lower than the acceleration voltage V (H) _min . Further, as shown in FIG. 9, the reference acceleration voltage (H) has a predetermined range and is not a single point value.

  As mentioned above, although this invention was concretely demonstrated based on the embodiment, this invention is not limited to the said embodiment. In the above embodiment, the charged particle beam irradiation state is set to the reference acceleration voltage, and the acceleration voltage is switched to a set acceleration voltage smaller than the reference acceleration voltage, so that the charged particle beam is not irradiated. The charged particle beam may be in a non-irradiated state by switching to a set acceleration voltage that is higher than the reference acceleration voltage.

  FIG. 4 shows a charged particle trajectory R2 when the acceleration voltage is switched to a set acceleration voltage larger than the reference acceleration voltage. In this case, the trajectory R2 travels radially outward from the orbital orbit R1 in the normal irradiation state, and the charged particles collide with the central electrode 31. Thereby, a charged particle beam can be made into a non-irradiation state.

  In the above-described embodiment, the set acceleration voltage is determined so that charged particles emitted from the ion source collide with the center electrode 32. For example, other center electrodes, acceleration electrodes, counter electrodes, phase A charged particle may collide with a slit, a wall, etc., and it may be in an unirradiated state.

  Moreover, although the said embodiment demonstrated application to the medical field of the charged particle beam irradiation apparatus (method) of this invention, for example, other fields, such as industrial radiation irradiation apparatuses, such as semiconductor wafer irradiation, are described. The present invention may be applied to a charged particle beam irradiation apparatus.

  DESCRIPTION OF SYMBOLS 1 ... Charged particle beam irradiation apparatus, 2 ... Cyclotron (accelerator), 6 ... Control apparatus (control means, setting acceleration voltage control means, arc voltage control means), 21 ... Ion source, 23, 24 ... Acceleration electrode, 31-33 ... center electrode.

Claims (6)

A charged particle beam irradiation apparatus for irradiating a charged particle beam to the irradiation object,
An ion source that generates charged particles;
An accelerator for accelerating the charged particles by applying an acceleration voltage to the charged particles generated by the ion source by an accelerating electrode, and emitting the charged particle beam;
And a control means for controlling the acceleration voltage,
Said control means, said a reference acceleration voltage the acceleration voltage of the irradiation state of the charged particle beam, the acceleration voltage by switching the reference acceleration voltage greater than or less than set acceleration voltage, the charged particle beam non-irradiation state A charged particle beam irradiation apparatus comprising: a set acceleration voltage control means. Said setting accelerating voltage control means, the electrode provided in the accelerator, so as to collide with the charged particles emitted from the ion source, according to claim 1 charged particle beam irradiation according to control said setting accelerating voltage Equipment . After switching to the set acceleration voltage, and arc voltage control means for generating the arc discharge in the ion source,
The charged particle beam irradiation apparatus according to claim 1, further comprising: the control unit that switches the acceleration voltage to the reference acceleration voltage after the occurrence of arc discharge. A charged particle beam irradiation apparatus control method for generating charged particles with an ion source, accelerating the generated charged particles with an accelerator to emit a charged particle beam, and irradiating the irradiated body with the charged particle beam,
A charged particle generation step of generating the charged particles by the ion source;
And a control step of controlling the acceleration voltage to the acceleration electrode of the accelerator is applied to the charged particles accelerate the charged particles,
Wherein the control step, the referenced acceleration voltage the acceleration voltage of the irradiation state of the charged particle beam, the acceleration voltage by switching the reference acceleration voltage greater than or less than set acceleration voltage, the charged particle beam non-irradiation state A charged particle beam irradiation apparatus control method comprising: a set acceleration voltage control step. Said setting accelerating voltage control step, the electrode provided in the accelerator, so as to collide with the charged particles emitted from the ion source, according to claim 4 charged particle beam irradiation according to control said setting accelerating voltage Control method of the device . After switching to the set acceleration voltage, and arc voltage control step of generating an arc discharge in the ion source,
The method for controlling a charged particle beam irradiation apparatus according to claim 4, further comprising the control step of switching the acceleration voltage to the reference acceleration voltage after the occurrence of arc discharge.

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