JPH1033697A - Charged particle beam radiating device and medical treatment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the radiation of dose in the case where a charged particle beam radiating device using a wobbler electromagnet and a scatterer damages the wobbler electromagnet and the soundness of a system, and improve the safety of the device. SOLUTION: This charged particle beam radiating device comprises electromagnets 10, 11 for generating an electromagnetic field for deflecting a charge particle beam, an electromagnetic field generating device including a.c. power sources 12, 13, and a scatterer for scattering a charged particle beam. In this case, a shield 15 is disposed between the electromagnetic field generating device and the scatterer 14, or on downstream from the scatterer 14, or in both positions. If the soundness of a system is damaged and a beam axis is shifted from a preset value, the charged particle beam is stopped by the shield 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charged particle beam irradiation apparatus for a charged particle beam therapy apparatus, and more particularly to an irradiation field forming apparatus.

[0002]

2. Description of the Related Art In this kind of charged particle beam irradiation apparatus, a wide and flat irradiation dose distribution is realized by an irradiation field expanding apparatus, and an irradiation range is limited by a collimator downstream of the irradiation field expansion apparatus.

[0003] As a conventional charged particle beam irradiation field expanding apparatus, there is a review of Scientific Instruments Vol. 64 No. 8
As discussed in (August 1993) pp. 2055 to 2122, a method of scattering charged particle beams from an accelerator through a plate made of a material such as lead is used. The plate made of lead or the like is called a scatterer. As a method using a scatterer, there has been a method (wobbler method) using a combination of a rotating electromagnetic field and a scatterer. Also, Procee
dings NIRS International Seminar on the Applicatio
n of Heavy Ion Accelerator to Radiation Therapy of
Cancer in connection with XXI PTCOG Meeting (19
(November 1994), pages 100 to 114, there is also a method using two types of scatterers.

FIG. 10 shows the configuration of a conventional irradiation field enlarging apparatus using the wobbling method. Two sets of deflecting means 10 and 11 are provided on the charged particle beam axis, and the phases are shifted by 90 degrees.
The beam axes are deflected in directions orthogonal to each other. By the two sets of deflecting means 10 and 11, the traveling direction of the charged particle beam draws an ellipse as shown in the figure. Downstream of the deflecting means, a metal plate (scatterer 14) is arranged to scatter the charged particle beam.

FIG. 12 shows a graph of an irradiation dose distribution (particle distribution) by the wobbling method. The irradiation dose distribution at an arbitrary moment during irradiation is a normal distribution centered on the beam axis when there is no scatterer (curve in a in FIG. 12), but since the beam axis is rotated by the wobble electromagnet, the irradiation dose is Is flattened (curve b in FIG. 12). By adjusting the rotation radius of the beam axis and the thickness of the scatterer 14, the spatial distribution of the irradiation dose can be adjusted. Therefore, in the charged particle beam therapy, the radius of rotation of the beam axis and the thickness and material of the scatterer 14 are set so as to uniformly irradiate the charged particle beam irradiation area. Extra beams outside the irradiation range are stopped by the collimator.

FIG. 11 is a graph showing a device configuration of a conventional irradiation field enlarging device using a wobbling method and a spatial distribution of a dose of a charged particle beam at an affected part. As the deflecting means, electromagnets (wobbler electromagnets) 10 and 11 that supply alternating-current power with a 90-degree phase shift from the alternating-current power supplies 12 and 13 to generate alternating magnetic fields in directions orthogonal to each other are used. During normal operation, a flat irradiation dose distribution is realized around the center of rotation of the beam axis as shown in FIG. 11A. Japanese Patent Application Laid-Open Nos. 2-49670 and 6-86833 disclose a technique for flattening the particle dose. However, when the amount of excitation of the wobble electromagnet decreases, the radius of rotation of the beam axis changes, and the irradiation dose distribution changes as shown in the lower part of FIG. 11B.

FIG. 13 shows the spatial distribution (time average) of the irradiation dose when the radius of rotation of the beam axis is changed while keeping the thickness of the scatterer constant. The radius of rotation of the beam axis at which the irradiation dose distribution became flat within a range of 60 mm from the center of rotation of the beam axis was R = 1.0. When the amount of excitation of the wobbler electromagnet is reduced to half or zero, the dose distribution becomes R = 0.
5. The distribution shown in the graph of R = 0. It can be seen that the irradiation dose near the center of rotation of the beam axis at R = 0 is about three times that during normal operation.

For this reason, in the conventional charged particle beam therapy apparatus, in order to obtain the irradiation dose distribution planned in the treatment plan, the normal operation of each device and the trajectory, current, and distribution of the charged particle beam are as follows. Normalness was detected by various monitors. For that purpose, many charged particle beam measuring instruments are arranged between the charged particle beam generator and the irradiation of the affected area,
By measuring the irradiation dose, charged particle beam position, irradiation distribution, etc., the health of the operating condition of the treatment device was diagnosed.
In addition, to confirm that the irradiation field expansion device is operating normally, a multi-channel position measurement device that measures the distribution of charged particle beams is placed downstream of the irradiation field expansion device, and the flatness of the irradiation amount is reduced. It was measured directly. These conventional safety measures use an active method of controlling devices based on the information of the system soundness diagnosis.

[0009]

Generally, charged particle beam therapy using a proton beam or a heavy particle beam has the advantage that the positional resolution of dose irradiation is good and the dose can be accurately irradiated to an affected part. In addition, in particular, in the case of heavy ion beams, a biological effect due to radiation irradiation is high, so that a tumor with low radiation sensitivity has a high therapeutic effect. However, the dose to normal tissues other than the affected area must be reduced to the minimum dose expected at the time of treatment planning. If the operation of each device deviates from the design value, the irradiation dose distribution changes, and the treatment cannot be performed as planned.

It is an object of the present invention to provide a conventional method of controlling equipment based on information on system soundness diagnosis, and furthermore, to prevent dose irradiation when the soundness of the system is impaired. Is to be further improved.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an apparatus for expanding an irradiation field by the Wobbler method, wherein an electromagnetic field generator for deflecting a charged particle beam and a scatterer, or downstream of the scatterer, or both. At the position, the shield does not interfere with the beam axis of the charged particle beam after being deflected by the electromagnetic field generator at the position and intersects with the passing area of the charged particle beam when the excitation state of the electromagnetic field of the electromagnetic field generator is not normal. Is achieved.

Further, the above object is achieved by providing means for detecting the amount of current flowing to the shield, and means for controlling charged particle beam irradiation based on the detection signal.

According to the above-described means, when the excited state of the electromagnetic field generator is normal, the charged particle beam after deflection does not interfere with the shield and irradiates the affected part with a predetermined dose of the charged particle beam. However, when the excitation state is not normal, such as when the electromagnetic field generator is not excited, the passing area of the charged particle beam changes, and a shield exists in the changed area. You. Thereby, the dose is accurately irradiated to the affected part, but the irradiation to normal tissues other than the affected part is suppressed.

Further, the shield is made of metal, and by detecting the amount of current flowing when the charged particle beam crosses the metal, it is possible to accurately detect the change state of the passage area of the charged particle beam. Therefore, by controlling the charged particle beam irradiation based on this detection signal, it is possible to surely prevent the irradiation to a part other than the affected part when the irradiation is not normal.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows the configuration of the charged particle beam therapy system according to the first embodiment of the present invention. The accelerator system 1 comprises an ion source 2, a pre-accelerator 3, and a synchrotron 4.
Generates high energy particle beams required for treatment. The particle beam accelerated by the synchrotron is extracted out of the synchrotron as a pulse beam having a length of about 0.5 seconds using a technique called slow extraction, and the extracted particle beam is expanded in the irradiation field The beam shape is shaped into the affected part shape by the device 5 and the collimator 6. Also,
The energy distribution is adjusted by the range shifter 7 and the ridge filter 8, and the adjusted charged particle beam is irradiated to the patient 9. Note that each device is set so that the irradiation dose in the irradiation area planned in the treatment plan is high.

FIG. 1 is a graph showing the configuration of the irradiation field enlarging device 5 according to the first embodiment of the present invention and the spatial distribution of the dose of the charged particle beam at the affected part.

A shield 15 is arranged downstream of the wobbler electromagnets 10 and 11 and upstream of the scatterer 14. FIG. 3 shows the shield 15 as viewed from the beam axis upstream side. Shield 15
Is a beam axis-shaped slit 16 of an elliptical cylindrical charged particle beam deflected so as not to interfere with the beam passage area during normal operation.
During normal operation, the charged particle beam passes through the slit 16 and can obtain the same charged particle distribution as in the related art (FIG. 1A, bottom). However, if the soundness of the wobble electromagnet is impaired, the excitation amount is reduced, and the beam axis shifts, the beam collides with the shield 15. The thickness of the shield 15 in the beam traveling direction is set to be larger than the maximum range of the charged particle beam used for the treatment. Then, the beam that has collided with the shield 15 stops completely (FIG. 1B, lower).

FIG. 5A shows a region where the beam 19 collides with the shield 15 when the amount of excitation of the wobble electromagnet increases. FIG. 5B shows a region where the beam 19 collides with the shield 15 when the amount of excitation of the wobble electromagnet is reduced. In these cases, no irradiation is performed because the beam is completely stopped. FIG. 6A shows a region where the beam 19 collides with the shield 15 when the excitation amount of one of the two wobble electromagnets is reduced, and FIG.
FIG. 8A shows a region where the beam 19 collides with the shield when the excitation amount of one of the two wobble electromagnets is increased. FIG. 8A shows the phase of the time change of the magnetic field strength of the two wobble electromagnets. The area where the beam 19 collides with the shield when the angle is shifted from 90 degrees is shown. Shield 15 in each case
As a result, most of the beams are stopped, so that the irradiation amount is reduced.

FIGS. 6B, 7B, and 8B show the irradiation dose distribution in each case in a contour map. FIG. 6C, FIG. 7C, and FIG.
Shown in 4A and 4B show the beam passage area and the irradiation dose distribution during normal operation.

FIG. 9 shows the configuration of a charged particle beam therapy system according to a second embodiment of the present invention. An ammeter 18 is connected to a shield 15 made of metal such as lead, and the measured value (i) of the ammeter
Is output to the determination device 20. When the beam hits the shield 15, a larger current flows than in the normal state. Therefore, the determination device 20 sets a current in advance and a current exceeding the allowable range (i0) stored in the storage device 21 flows to the shield 15. In this case, it is determined that the beam has collided with the shield 15, and a signal is output to the synchrotron operation control unit 22. Upon receiving the signal, the operation control unit 22 displays a warning notifying the abnormality of the system on the display device 23 and stops emitting the beam.

In the case where erroneous irradiation is performed as described above, irradiation can be stopped, and the amount of irradiation until the irradiation is stopped can be reduced.

The control is not limited to the synchrotron control, and the deflection of the beam can be corrected by controlling the electromagnetic field generator.

Further, by detecting and controlling the current, the irradiation can be stopped when the thickness, shape, etc., of the shield are not sufficient or abnormal.

The shield 15 is located downstream of the scatterer 14,
You may arrange | position at the position which does not interfere with a beam passage area.

The irradiation field forming apparatus of the present invention can also be used when the charged particle beam generator is other than a synchrotron.

[0027]

As described above, according to the present invention, when the wobble electromagnet is operating normally, the irradiation area required for treatment is evenly irradiated, and when the soundness of the wobble electromagnet is impaired. , Reduce the dose exposure to the patient. Thereby, the safety of the charged particle beam therapy system is improved.

In a state where the system operates normally and the charged particle beam axis follows a trajectory as designed, the irradiation area required for treatment is evenly irradiated, and the soundness of the system is impaired. When the particle beam axis deviates from the design value trajectory, the dose irradiation to the patient is reduced. In addition, the abnormality of the system is immediately indicated to the accelerator driver, and the charged particle beam therapy is stopped. Thereby, the safety of the charged particle beam therapy system can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a device configuration of an irradiation field enlarging device and a spatial distribution of irradiation dose according to a first embodiment of the present invention.

FIG. 2 is a system configuration diagram according to the first embodiment of the present invention.

FIG. 3 is a block diagram of a shield viewed from an upstream part of a beam axis.

FIG. 4 is a distribution diagram of a beam passing area and a dose in a normal operation.

FIG. 5 is a diagram showing a beam passing area when the soundness of the electromagnet is impaired.

FIG. 6 is a diagram showing a beam passage area and an irradiation dose distribution when the soundness of the electromagnet is impaired.

FIG. 7 is a diagram showing a beam passage area and an irradiation dose distribution when the soundness of the electromagnet is impaired.

FIG. 8 is a diagram showing a beam passage area and an irradiation dose distribution when the soundness of the electromagnet is impaired.

FIG. 9 is a system configuration diagram according to a second embodiment of the present invention.

FIG. 10 is a configuration diagram of a conventional irradiation field enlarging device.

FIG. 11 is a diagram showing a device configuration and a spatial distribution of irradiation dose of a conventional irradiation field expansion device using a wobbling method.

FIG. 12 is an irradiation dose distribution diagram by the wobbling method.

FIG. 13 is a diagram illustrating a change in the spatial distribution of the irradiation dose when the radius of gyration of the beam axis is changed.

[Explanation of symbols]

1. Accelerator system, 2. Ion source, 3. Pre-accelerator,
4 synchrotron, 5 irradiation field expander, 6 collimator, 7 range shifter, 8 ridge filter, 9 patient, 11 wobbler electromagnet, 12 13 AC power supply, 14 scatterer, 15 Shield, 16 slits,
18 ... ammeter, 19 ... beam, 20 ... judgment device, 21 ...
Storage device, 22: synchrotron operation control unit, 23: display device.

Claims (5)

[Claims] 1. A charged particle beam irradiation apparatus comprising, as constituent elements, an electromagnetic field generator for generating an electromagnetic field for deflecting a charged particle beam and a scatterer disposed downstream of the electromagnetic field generator for scattering the charged particle beam. At a position between the electromagnetic field generator and the scatterer, or downstream of the scatterer, or at both positions, does not interfere with the beam axis of the charged particle beam after being deflected by the electromagnetic field generator at the position, and generates the electromagnetic field. A charged particle beam irradiation apparatus characterized in that a shield is disposed in a region intersecting with a passage region of a charged particle beam when an excitation state of an electromagnetic field of the device is not normal. 2. The charged particle beam irradiation apparatus according to claim 1, wherein the shield is made of metal. 3. The shield according to claim 2, wherein the shield is a cylindrical body having a slit formed in a bee-axis shape of an elliptic cylindrical charged particle beam deflected by the electromagnetic field generator or scattered by the scatterer. 2. The charged particle beam irradiation apparatus according to 1. 4. A charged particle beam irradiation apparatus comprising, as constituent elements, an electromagnetic field generator for generating an electromagnetic field for deflecting a charged particle beam and a scatterer disposed downstream of the electromagnetic field generator for scattering the charged particle beam. At a position between the electromagnetic field generator and the scatterer, or downstream of the scatterer, or at both positions, does not interfere with the beam axis of the charged particle beam after being deflected by the electromagnetic field generator at the position, and generates the electromagnetic field. In a region where the excited state of the electromagnetic field of the device is not normal and intersects with the passage region of the charged particle beam, a metal shield is arranged, and means for detecting the amount of current flowing to the shield, based on the detection signal, A means for controlling charged particle beam irradiation. 5. A charged particle beam therapy apparatus comprising the charged particle beam irradiation apparatus according to claim 1. Description: