JPH0999108A - Charged particle beam equipment - Google Patents

Abstract

(57) Abstract: A target is irradiated uniformly or the irradiation amount is controlled with a desired distribution even if the intensity of a charged particle beam varies with time. In a charged particle beam device that irradiates an emitted charged particle beam onto a target in a required range while scanning the target, a time change N (t) of the intensity of the charged particle beam is measured to determine the scanning speed of the charged particle beam. When expressed as v (t), the scanning speed is controlled so that N (t) / v (t) is constant or within a predetermined range. As a result, even if the intensity of the charged particle beam fluctuates with time, it is possible to irradiate the irradiation target with a uniform or required dose distribution, and a device for keeping the charged particle beam intensity constant in time is unnecessary, The cost of the entire system can be reduced.

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 system, and more particularly to a charged particle beam system suitable for use in cancer treatment and diagnosis of affected areas.

[0002]

As a conventional charged particle beam device, Rev.
The one described on page 2088 of Sci. Instrum., Vol. 64, No8, August, 1993 is known. A charged particle beam device according to this conventional technique will be described with reference to FIG.

When a charged particle beam emitted from a charged particle beam device is applied to a target (for example, a diseased part), the target has a certain area, not a single point, and therefore the beam is moved up and down.
It is necessary to scan right and left so that the required area is uniformly irradiated. In FIG. 12, 172 is a charged particle beam, which travels in the Z-axis direction. Reference numeral 101 is an X-direction deflection electromagnet, and 102 is a Y-direction deflection electromagnet perpendicular to the X direction.
When a time-varying current is passed through the electromagnets thus arranged, the magnetic fields generated by the deflection electromagnets 101 and 102 also change with time, and the charged particle beam 172 is horizontally scanned by the deflection electromagnet 101. Bending electromagnet 1
02 scans vertically. By increasing the number of scans (reciprocations) per unit time in the horizontal direction and relatively decreasing the number of scans per unit time in the vertical direction,
An irradiation field as shown in the rectangular area 99 can be formed.

When sinusoidal currents having the same frequency but different phases by 90 degrees are applied to the bending electromagnet 101 and the bending electromagnet 102,
The strengths of the magnetic fields of the bending electromagnet 101 and the bending electromagnet 102 change sinusoidally at the same frequency with respect to time, and
Each phase is different by 90 degrees. As a result, the charged particle beam is circularly scanned in the irradiation field.

As a prior art relating to a charged particle beam device for medical use, there is, for example, Japanese Patent Laid-Open No. 6-339541.

[0006]

In the conventional charged particle beam apparatus, the charged particle beam is scanned using the X-direction deflection electromagnet and the Y-direction deflection electromagnet to irradiate the target. However, when the intensity of the charged particle beam changes with time, it becomes difficult to uniformly irradiate the irradiation field that cuts the lesion with a plane perpendicular to the beam traveling direction, and only the strongly irradiated part and weakly irradiated part can be used. The parts that are not irradiated are mixed,
The lesion may remain. Further, when irradiating a lesion of a certain size and shape with a charged particle beam, it is difficult to uniformly irradiate the entire lesion even in the depth direction.

An object of the present invention is to provide a charged particle beam device capable of uniformly irradiating a target and controlling the irradiation amount with a desired distribution even if the intensity of the charged particle beam varies with time. It is in.

[0008]

In the charged particle beam apparatus for irradiating an emitted charged particle beam on a target in a required range while scanning the target, an intensity measuring means for measuring the time change of the intensity of the charged particle beam. And a control means for controlling the scanning speed of the charged particle beam in proportion to the measured value of the intensity.

In the charged particle beam apparatus for irradiating a target in a required range with the emitted charged particle beam while scanning the target, a distribution measuring means for measuring the spatial distribution of the dose of the charged particle beam, and an irradiation target. Control means for calculating the target irradiation amount at each scanning position of the area, and means for controlling the intensity of the charged particle beam to be irradiated based on the deviation between the measured value of the distribution measuring means and the target irradiation amount are provided. Will be achieved.

When the charged particle beam intensity is high, the beam scanning is accelerated, and when the charged particle beam intensity is reduced, the scanning speed is suppressed, whereby the spatial distribution of the irradiation dose can be made uniform. That is, the scanning speed is controlled so as to be substantially proportional to the charged particle beam intensity. When scanning is performed with an electromagnet, the speed of beam scanning is proportional to the rate of change of the magnetic field, and the rate of change of the magnetic field is
Generally, it is proportional to the rate of change of the electromagnet current. Therefore, based on the measured value of the beam intensity, the electromagnet power source is controlled so that the current change rate of the electromagnet is proportional to the beam intensity. Also, when beam scanning is performed by an electrostatic deflector, the scanning speed is proportional to the rate of change of the deflector voltage, so a uniform irradiation intensity is achieved by applying a voltage proportional to the change in beam intensity. it can.

When the accelerated charged particle beam is emitted to irradiate the target, the target irradiation amount distribution is determined in advance, and the spatial distribution of the irradiation amount is measured while scanning the charged particle beam. However, since the beam intensity at the target position and the position of the spatial distribution measuring means are different, considering the position and depth of the target,
Calculate the target value of the irradiation dose distribution. Then, based on this measurement result, the integrated dose is calculated and the difference from the target value is calculated.
Whether to continue or stop the irradiation is determined, and in the next scanning process, the irradiation is stopped at the place where the irradiation needs to be stopped. However, the beam extraction is stopped and the intensity of the deflector is continuously changed, and when the irradiation reaches a position where the irradiation is required, the beam is extracted and the irradiation is performed. At the same time, the beam intensity distribution is measured,
For the position where the target dose was reached during irradiation,
Stop the beam. By repeating these procedures, irradiation can be performed according to the target irradiation dose distribution.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a charged particle beam system according to a first embodiment of the present invention. In this embodiment, low-energy ions are made incident on the synchrotron type accelerator 100 from the pre-stage accelerator 98, and after acceleration, are emitted to the treatment room 111. This ion beam is applied to the rotary irradiation device 110.
(This is installed in the treatment room 111.) and is used for cancer treatment.

FIG. 2 is a diagram showing an example of the relationship between the depth inside the body and the irradiation dose of the ion beam. The peak of the irradiation dose in FIG. 2 is called a Bragg peak, but the position of the Bragg peak changes depending on the energy. Therefore, the patient information such as the depth of the affected area is input to the control device 130 of FIG. 1, and the control device 130 calculates the magnitude of the required acceleration energy based on the patient information. Then, after the beam is incident on the accelerator 100 from the pre-stage accelerator 98, the controller 130
The power source 165 of the accelerator 100 is controlled on the basis of the control signal from ## EQU1 ## to accelerate the ion beam to the required energy.

When the accelerated beam is emitted from the accelerator 100 to the treatment room 101, it utilizes the resonance phenomenon of the vibration of the beam and is emitted from the beam with increased vibration. The resonance phenomenon is controlled by the quadrupole electromagnet 145 in the accelerator. In the extraction process, the intensity of the emitted beam changes as shown in FIG. 3 as the amount of excitation of the quadrupole electromagnet 145 that controls resonance is changed by the accelerator power supply 165.

The beam 172 emitted from the accelerator 100 and introduced into the treatment room 111 via the transportation system 171 is irradiated to the patient by using the rotary irradiation device 110. Rotating irradiation device 1
In 10, the quadrupole electromagnet 150 and the deflection electromagnet 151 are used to supply a necessary current from the power supply 170 based on the beam energy signal from the control device 130 to transport the beam downstream.

Scanning electromagnets 120 and 121 are installed on the downstream side of the rotary irradiation device 110, and two-dimensionally scans the beam in the x and y directions within a plane perpendicular to the beam traveling direction. The scanning range of the scanning electromagnet is calculated by the control device 130 based on the patient information, and the power supply 160 of the scanning electromagnet is controlled based on this result. A beam intensity detector 140 is installed in the rotary irradiation device 110 to measure a temporal change in beam intensity. The beam intensity detector 140 may be a device that electromagnetically measures the beam current or a device that directly detects the number of particles in the beam.

In the present embodiment, the scanning speed of the beam is increased when the beam intensity is high and is decreased when the beam intensity is weak, so that the ion beam dose is always uniform over the entire irradiation field of the affected area. To control. The beam intensity at a certain point is expressed as N (t) [1 / s], and the scanning speed is v
When expressed as (t) [m / s], the beam intensity per unit length is N (t) / v (t). Therefore, to keep the beam intensity per unit length constant, N (t) / v (t)
Should be constant (v (t) is also zero when N (t) is zero), which enables irradiation with a uniform distribution. Therefore, based on the detection result of N (t) obtained by the beam intensity detector 140, N (t) / v (t) becomes constant,
The controller 130 controls the power supply 160 of the scanning electromagnet.

FIG. 4 is an equivalent circuit diagram of the scanning electromagnet, and FIG. 5 is a flow chart showing the control method thereof. In FIG. 4, R is the resistance of the scanning electromagnet and L is the inductance of the scanning electromagnet, and these values are obtained in advance. The scanning speed v (t) is the current I of the scanning electromagnet.
Is proportional to the time change rate dI / dt. Therefore, in step 1 of FIG. 5, the current value I of the scanning electromagnet at time t is obtained. At the same time as this step 1, step 2
The beam intensity N (t) is measured by the detector 140 (FIG. 1). Then, with the proportional constant being Con, the required current change rate dI / dt = Con · N (t) is obtained by the controller 130.

Next, in step 3, the voltage Vmag applied to the scanning electromagnet is Vmag = RI + L.dI / dt = RI + L.Con.
Calculate as N (t). Then, the voltage obtained in step 3 is applied from the power supply 160 to the scanning electromagnet (step 4).
The procedure of steps 1 to 4 is performed according to the maximum value Imax of the current value of the scanning electromagnet determined in advance by the controller 130.
Repeat until. It should be noted that these calculations and controls are performed for the scanning electromagnets in the x direction and the y direction.

By the above control, the current change rate of the scanning electromagnet becomes similar to the time change of the beam intensity shown in FIG.
Ratio N (t) / V of temporal change in beam intensity N (t) [1 / s] and scanning speed V (t) proportional to current change rate
It is possible to keep (t) constant. As a result, the spatial distribution of irradiation dose becomes uniform.

In the above-described embodiment, the beam is scanned linearly in a zigzag manner on the irradiation target. However, in the case of scanning on an arc, or in the case of expanding the beam in a plane and scanning it vertically to the plane. Also, by controlling the scanning electromagnet in the same manner, the same effect can be obtained.

Further, although the electromagnet is used for the deflector in the above-mentioned embodiment, when the electrostatic deflector is used, the rate of change of the voltage Vinf applied to the electrostatic deflector is proportional to the scanning speed. The voltage Vinf is calculated by Vinf = Con2 · N (t) (Con2: constant), and by applying it to the electrostatic deflector, irradiation can be performed with a uniform distribution as in the case of scanning with an electromagnet.

FIG. 6 is a block diagram of a charged particle beam system according to the second embodiment of the present invention. The charged particle beam apparatus according to the present embodiment is basically the same as the apparatus configuration shown in FIG. 1, except that a beam spatial distribution measuring instrument 141 is used instead of the intensity detector 140 and a control apparatus 180 is newly added. It is attached. As in the first embodiment, the accelerator 100 emits light utilizing resonance of vibration of the beam.
During emission, the strength of the quadrupole electromagnet 145 is kept constant, and the stability limit of resonance is kept constant. On the other hand, a high frequency is applied to the beam from the high frequency device 175 to gradually increase the beam diameter,
Resonance is generated by exceeding the stability limit of resonance. The charged particle beam emitted is transported by the transport system 171 to the rotary irradiation device 1.
The scanning electromagnets 120 and 121 are used to scan the beam in a zigzag manner to irradiate the spread diseased part. Further, the beam intensity spatial distribution measuring device 141 is used to measure the beam intensity distribution immediately before the patient.

In the charged particle beam system of this embodiment, information about the affected part of the patient is input to the control unit 180. The input information includes the position and shape of the affected area, the history of irradiation treatment, the radiation dose absorbed by the affected area, and the like. The control device 180 divides the affected area into a number of layers in the depth direction, and determines various parameters necessary for controlling the accelerator and the scanning electromagnet according to the process of FIG. 7.

First, in step 11 of FIG. 7, the affected area is virtually divided into a large number of layers Li (i = 1, 2, ..., N).
In step 12, the energies of the beams for irradiating the affected areas of the respective depths are obtained from the depths of the affected areas in the respective layers Li, and are defined as E1, E2, ..., En. Next, in step 13, for each layer Li, the scanning range of the scanning electromagnets 120 and 121 is determined from the information on the spread and shape of the affected area. In the present embodiment, compared with the scanning speed of the scanning electromagnet 120 in the x direction in FIG.
Increase the scanning speed of 1. Therefore, the maximum value of the scanning electromagnet current in the y direction is set according to the current of the scanning electromagnet 120 in the x direction according to the shape of the affected part.

In the next step 14, for the layer Li,
Determine the target spatial distribution of beam dose. This is because when the Bragg peak shown in FIG. 2 is made to coincide with the position of the layer Li, as shown in FIG. 8, at a position shallower than the layer Li such as the layer Lj, irradiation corresponding to the plateau portion of FIG. 2 is performed. This is to prevent the occurrence of a portion where the absorbed dose is unnecessarily high. Therefore, when the Bragg peak is adjusted to the layer Li, the irradiation dose of the central region of the layer Li which has already been irradiated by the plateau portion is smaller than that of the non-irradiated portion of the plateau portion.

FIG. 9 is a flow chart showing the operation of the irradiation method and the device based on the calculation result of the processing in FIG. First, in step 21, the controller 130 controls the accelerator power supply 165 to accelerate the beam up to the beam energy Ei required by the controller 180 to irradiate the layer Li of the affected area based on the patient information. After accelerating, step 22
Then, the currents of the scanning electromagnets 120 and 121 are changed based on the signal from the control device 180 so that the beam can be scanned in the x direction and the y direction so as to match the shape of the affected part of the layer Li.

In the next step 23, the integrated intensity R (X, Y) of the beam at the position (X, Y) is converted to the target intensity T (X, Y).
Compare with When the integrated dose is smaller than the target value, a high frequency is applied to the beam from the high frequency device 175 in step 24 of FIG. When a high frequency wave is applied to the beam, the beam diameter increases, resonance occurs in the vibration of the beam, and the beam is emitted. In the next step 25, the dose at the position (X, Y) is measured by the beam intensity spatial distribution measuring device 141 (FIG. 6),
The integrated dose R (X, Y) is calculated.

On the other hand, in step 23, the integrated dose R (X,
When Y) has reached the target intensity T (X, Y), the process proceeds to step 26, the high frequency for emission is stopped, and
Stop beam emission. However, the currents of the beam scanning electromagnets 120 and 121 are changed in the same manner as when beam extraction is performed, and when beam extraction is performed by applying a high frequency, the irradiation position is controlled to change.

In step 27, these procedures are performed on the layer L.
The scanning is repeated until the surface i is scanned. When the scanning of the layer Li is completed, the process proceeds to step 28, where it is determined whether the integrated dose R (X, Y) has reached the target dose T (X, Y) at all points of the layer Li, and the target dose has been reached. If not, the beam is accelerated again to perform extraction and irradiation. Layer Li
The cumulative dose R (X, Y) is the target dose T (X,
Y), the process returns to step 11 and the layer Li
The beam energy is accelerated to Ei + 1 so as to irradiate +1 and beam scanning and irradiation are performed as described above. By repeating the energy change and the irradiation of the layer Li as described above, the affected area can be irradiated at the irradiation target dose.

FIG. 10 is a block diagram of a charged particle beam system according to the third embodiment of the present invention. This embodiment includes both the first embodiment and the second embodiment. The method described in the first embodiment irradiates with a uniform intensity distribution for each scan, and at the same time, as described in the second embodiment. The target irradiation dose distribution is determined in advance, and at the position where the target is reached, the high frequency for extraction is stopped and the extraction is stopped. In the case of this embodiment, the beam intensity detector 140 and the distribution measuring device 141 are both installed downstream of the scanning electromagnets 120 and 121 to control the beam scanning speed. The parameters necessary for irradiation are calculated in the same manner as in FIG.

FIG. 11 is a flow chart showing the operating procedure at the time of irradiation in the third embodiment. The difference from the flowchart in FIG. 9 is that the beam intensity N (t) is measured by the detector 140 (FIG. 10) in step 25 provided between step 24 and step 25, and the beam intensity N (t The point is to control the power supplies of the scanning electromagnets 120 and 121 so that the ratio of t) to the scanning speed v (t) becomes constant. As a result, even if the intensity of the beam emitted from the accelerator temporally varies, the target irradiation dose distribution can be realized in a shorter time than in the second embodiment.

In the above-mentioned embodiments, the case where the charged particle beam is irradiated to the affected area for treatment has been described. However, when the charged particle beam is used for tomographic imaging of the affected area such as ultrasonic CT and X-ray CT. It goes without saying that it is also applicable.

[0034]

According to the present invention, even if the intensity of the charged particle beam fluctuates with time, the irradiation target can be uniformly irradiated, and the irradiation dose distribution can be set regardless of the shape and size of the affected area. Can be controlled. Therefore, an apparatus or the like for keeping the charged particle beam intensity constant over time is not required, and the cost of the entire system can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a charged particle beam apparatus according to a first embodiment of the present invention.

FIG. 2 is a conceptual diagram showing a Bragg peak.

FIG. 3 is a diagram showing a temporal change in beam intensity.

FIG. 4 is a diagram showing an equivalent circuit of a scanning electromagnet.

FIG. 5 is a diagram showing a control algorithm of a scanning electromagnet.

FIG. 6 is a configuration diagram of a charged particle beam apparatus according to a second embodiment of the present invention.

FIG. 7 is a flowchart showing a parameter calculation procedure necessary for irradiation control.

FIG. 8 is a diagram showing superimposition of irradiation doses.

FIG. 9 is a flowchart showing an irradiation procedure.

FIG. 10 is a configuration diagram of a charged particle beam system according to a third embodiment of the invention.

FIG. 11 is a flowchart showing an irradiation procedure of the third embodiment.

FIG. 12 is a schematic configuration diagram of a conventional charged particle beam device.

[Explanation of symbols]

172 ... Charged particle beam, 101 ... X-direction scanning electromagnet,
102 ... Y direction scanning electromagnet perpendicular to the x direction, 99 ... Irradiation field, 98 ... Pre-accelerator, 100 ... Accelerator, 111 ... Treatment room, 110 ... Rotation irradiation device, 130 ... Control device, 145
… Quadrupole electromagnet, 165… Accelerator power supply, 120, 121…
Electromagnet for scanning, 160 ... Power source for electromagnet for scanning, 140 ...
Beam intensity detector, 141 ... Beam intensity spatial distribution measuring instrument, 170 ... Power source, 171 ... Transport system, 172 ... Beam, 175 ... High frequency device, 180 ... Control device.

Claims (11)

[Claims] 1. A charged particle beam apparatus for irradiating an emitted charged particle beam onto a target in a required range while scanning the target, and an intensity measuring unit for measuring a time change of the intensity of the charged particle beam, and a measured value of the intensity. A charged particle beam device comprising: a control unit that proportionally controls the scanning speed of the charged particle beam. 2. A charged particle beam apparatus for irradiating an emitted charged particle beam onto a target within a required range while scanning the target, and an intensity measuring unit for measuring a time change N (t) of the intensity of the charged particle beam; Beam scanning speed v
A charged particle beam apparatus comprising: a control unit that controls a scanning speed such that N (t) / v (t) is constant or within a predetermined range when expressed as (t). 3. The charged particle beam apparatus according to claim 1, wherein the control means controls the scanning speed by controlling the current of the scanning electromagnet. 4. The charged particle beam apparatus according to claim 1, wherein the control means controls the voltage of the electrostatic deflector to control the scanning speed. 5. The charged particle beam apparatus according to claim 1 or 2, wherein the intensity measurement by the intensity measuring means and the control of the scanning speed by the control means are performed during scanning of the charged particle beam. 6. A charged particle beam device for irradiating an emitted charged particle beam to a target in a required range while scanning the target, and a distribution measuring unit for measuring a spatial distribution of a dose of the charged particle beam, and an irradiation target area. Control means for calculating a target irradiation amount at the scanning position, and means for controlling the intensity of the charged particle beam to be irradiated based on the deviation between the measured value of the distribution measuring means and the target irradiation amount. Charged particle beam device. 7. A charged particle beam apparatus for irradiating a target within a required range while scanning an emitted charged particle beam, and a distribution measuring unit for measuring a spatial distribution of a dose of the charged particle beam, and a target of an irradiation target area. And a control unit for calculating a dose distribution, and a unit for irradiating a charged particle beam on the basis of the measurement value of the distribution measuring unit to control the dose applied to the irradiation target region to the target dose distribution. Charged particle beam device characterized by: 8. The charged particle beam according to claim 6 or 7, wherein the target irradiation amount or the target irradiation amount distribution at each scanning position is determined so that the irradiation amount is uniform over the entire irradiation target area. apparatus. 9. The charged particle beam device according to claim 6, wherein the means for controlling the intensity of the charged particle beam is a high frequency device. 10. The charged particle beam device according to claim 6, wherein the means for controlling the intensity of the charged particle beam is for controlling a charged particle generating means. 11. A charged particle beam device for irradiating an emitted charged particle beam onto a target in a required range while scanning the target, and an intensity measuring means for measuring a temporal change of the intensity of the charged particle beam, and a measured value of the intensity. Control means for proportionally controlling the scanning speed of the charged particle beam, distribution measuring means for measuring the spatial distribution of the irradiation amount of the charged particle beam, and control means for calculating the target irradiation amount at each scanning position of the irradiation target region. When,
A charged particle beam device comprising: a charged particle beam controlled by the control means; and a means for scanning so that the irradiation dose measured by the distribution measuring device becomes the target irradiation dose.