JP2021135111A - Feedback deflector system - Google Patents

Abstract

To provide a feedback deflector system that allows a beam to aim and illuminate in real time at an arbitrary location of a cancer target that is spread in a three-dimensional direction and moving and deforming.SOLUTION: A feedback deflector system is configured to include a correction deflector for correcting an irradiation position of a particle beam from a set value to a current position, and a drive power supply circuit for forming an excitation current waveform similar to that of a main deflecting electromagnet on the correction deflector in a time zone until the exciting current waveform of the main deflecting electromagnet of the accelerator for supplying the particle beam reaches a maximum value.SELECTED DRAWING: Figure 3

Description

The present invention relates to a feedback deflector system that spreads in a three-dimensional direction and makes it possible to irradiate a beam by aiming at an arbitrary position of a moving / deforming gun target in real time.

In next-generation particle beam therapy, the beam taken from the accelerator of the particle beam (also simply called "beam") is not only scanned and irradiated on the surface (two-dimensional) of the irradiation target, but also in depth. It is required to move the beam three-dimensionally including the direction and continuously irradiate the beam. A study on them is disclosed in Non-Patent Document 1-7.

Since the gun is not only wide but also thick, it is ideal in particle beam gun therapy to be able to continuously scan the particle beam in three dimensions throughout the gun.

For two-dimensional scanning of the particle beam, a pulse electromagnet (hereinafter referred to as "programming deflector") may be placed between the accelerator and the irradiation target, and the beam may be shaken at a required angle.

Here, the particle beam energy in the accelerator is extracted from the time when the value having the Bragg peak on the surface of the irradiation target is reached, and the beam is irradiated until the time when the energy corresponding to the Bragg peak at the deepest part of the irradiation target is reached. The beam spill is continuously pulled out (take-out time t1 to t2 in FIG. 5, Non-Patent Document 7).

At this time, if the magnetic field of the deflector is constant, the beam irradiation position at the target changes as the beam energy increases. In order to prevent this, first, the kick angle (maximum excitation value) of the setting deflector that is programmed in advance according to the position to be irradiated is determined for each excitation pulse, and the magnetic field synchronized with the excitation pattern of the main deflection electromagnet of the accelerator is set. Need to be generated in. This can be easily achieved with an appropriate drive power supply circuit and its operation program control (this system is called a "program operation deflector system" as shown in FIG. 1).

However, the program operation deflector system alone can only handle cases where the gun target does not move. The actual cancer target moves and deforms (changes) due to the influence of gravity due to breathing and other movements of the patient. However, the change is very slow compared to the beam irradiation time per shot (10 to 20 milliseconds), and it is almost stationary when viewed from the irradiation beam.

However, during the 10 Hz repetition, the gun target moves and deforms. Moreover, the movement and deformation do not move in exactly the same pattern. It depends on the patient and the operation of the irradiation bed on which the patient is placed. This cannot be handled by the program operation deflector system.

In addition to the program operation deflector system, it is necessary to construct a system (referred to as "feedback deflector system", see FIG. 1) corresponding to a gun target that moves and deforms in time according to each case.

Since the cancer target to be irradiated moves due to the physiological action of the human body such as respiration, it was a problem to first detect the position of the cancer target (cancer target profile) in real time. Fortunately, with the advent of a cancer target detection system that combines labeling with gold nanoparticles of a cancer target and an X-ray camera, that problem has already been solved (Patent Document 1).

On the other hand, by detecting the prompt gamma rays generated from the beam irradiated to the gun, the profile of the irradiation beam in the traveling axis direction (z-axis) of the irradiation beam, that is, the depth of the cancer target (dose profile in the z-axis direction) ) Signal detection has become possible (Non-Patent Document 8).

The 3D dose profile of the beam radiated to the gun target by using the dose profile signal in the z-axis direction and the 2D beam profile signal in the xy-axis direction on the beam position monitor placed just before the beam enters the human body ( Signal) can be grasped.

The "misalignment" of the position of the cancer target is determined by comparing the cancer target profile, which indicates the current position of the cancer target before beam irradiation, detected in real time by a computer with the 3D dose profile acquired during the previous beam irradiation. Ask. With the current computer processing technology, processing at 10 Hz is possible.

The biggest issue is how to correct the "misalignment" of the obtained cancer target position by the next beam irradiation.

Japanese Unexamined Patent Publication No. 2016-144573 (Image processing device and particle beam therapy device / Hitachi, Ltd., Hokkaido University) Japanese Patent Application Laid-Open No. 2006-31013 (All kinds of ion accelerators and their control methods / KEK)

Marco Schippers, “Advances in Beam Delivery Techniques and Accelerators in Particle Therapy”, Chapter 4 in Advances in Particle Therapy edited by Manjit Dosanjh and Jacques Bernier (CRC Press, 2018). T. Harberer et al., “Magnetic scanning system for heavy ion therapy”, Nucl. Instr. Meth. A 330, 296 (1993). M. Tomizawa et al., “Slow beam extraction at TARN II”, Nucl. Instr. Meth. A 326, 399 (1993). K. Noda et al., “Slow beam extraction by a transverse RF field with AM and FM”, Nucl. Instr. Meth. A 374, 269 (1996). M. Benedikt, P. Bryant, and M. Pullia, “A new concept for the control of a slow-extracted beam in a line with rotational optics”, Nucl. Instr. Meth. A 430, 523 (1999). W. Chu, B.A. Ludewigt, and T.R. Renner, “Instrument of cancer using proton and light ion beams”, Rev. Sci. Instrum. 64, 2055 (1993). Leo Kwee Wah, Takumi Monma, Toshikazu Adachi, Tadamichi Kawakubo, Tanuja Dixit, and Ken Takayama, “Compact hadron driver for cancer therapies using continuous energy sweep scanning”, Phys. Rev. Accelerators and Beams 19, 042802 (2016). Ayako Koide et al., “Precision imaging of 4.4 MeV gamma rays using a 3-D position sensitive Compton Camera” Nature, Scientific Reports 8, 1-9 (2018).

Therefore, the present invention makes it possible to irradiate a beam by aiming at an arbitrary position of a moving / deforming gun target in real time, that is, a gun target before beam irradiation detected in real time. It is an object of the present invention to provide a feedback deflector system that corrects the "misalignment" between the position and the position of the gun target at the time of the previous beam irradiation.

(1)
A correction deflector that corrects the irradiation position of the particle beam from the set value to the current position,
A drive power source that causes the correction deflector to form an exciting current waveform similar to the exciting current waveform of the main deflecting electromagnet in the time zone until the exciting current waveform of the main deflecting electromagnet of the accelerator that supplies the particle beam reaches the maximum value. Circuit and
A feedback deflector system characterized by consisting of.
(2)
The drive power supply circuit causes the correction deflector to generate a magnetic flux strength that corrects the position of the gun target profile from the three-dimensional dose profile of the gun target at the time of the previous particle beam beam irradiation to the position of the gun target profile before the particle beam beam verification. The feedback deflector system according to (1), wherein the irradiation position of the particle beam is corrected from the set value to the current position.
And said.

According to the present invention, the exciting current waveform generated by the correction deflector becomes similar to the exciting current waveform of the main deflection electromagnet of the accelerator. Further, the magnetic field of the correction deflector (Sn1 & Sn2) is changed by changing the ON / OFF timing of the thyristor Sc that controls the charging voltage of the capacitor C and the thyristor (Sp1 & Sp2) and (Sn1 & Sn2) that control the direction of the current to the correction deflector. The maximum amplitude of the exciting current waveform) can be changed including positive and negative. Combined with the features of continuous beam extraction from the accelerator (Fig. 5, Non-Patent Document 7) while sweeping this operation and energy, the three-dimensionally accurate three-dimensional target of the organ that moves and deforms three-dimensionally. Tracking beam irradiation becomes possible.

FIG. 1 is a particle beam gun therapy irradiation image diagram including the feedback deflector system of the present invention. FIG. 2 is a schematic cross-sectional view of the correction deflector of the present invention. FIG. 3 is a circuit diagram of the feedback deflector system of the present invention. FIG. 4 is a simulation result based on the operating principle of the circuit of FIG. FIG. 5 shows the continuous beam extraction of Non-Patent Document 7.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the following examples.

The feedback deflector system 1 of the present invention shown in FIG. 1-3 realizes beam emission capable of finely adjusting (real-time correction) the beam irradiation position in the three-dimensional direction according to the movement of the gun target. As shown in 2, it consists of a drive power supply circuit and a correction deflector. For the symbols of the circuit in FIG. 3, refer to the explanation of the symbols.

The accelerator of FIG. 1 can be exemplified by the induced acceleration synchrotron (Patent Document 2) shown in Patent Document 2, the beam extraction control system is an induced accelerator cell, and the particle beam beam accelerated and extracted by the accelerator changes energy as shown in FIG. The extraction method is disclosed in Non-Patent Document 7. The beam extraction timing control signal is a signal corresponding to the extraction time (t1, t2) given from the deviation obtained by the feedback computer. The program operation deflector system has the same configuration as the feedback deflector system except that the charging time to the drive power supply circuit is preset. The charging time control signal is a charging time signal required to generate a magnetic field that realizes the required deflection angle of the correction beam with the correction deflector.

The correction deflector of FIG. 2 is a deflecting electromagnet that suppresses the demagnetization effect due to eddy current even at 10 Hz operation and prevents heat generation because the vacuum duct to be inserted into the gap is manufactured by a thin SUS elliptical pipe.

According to the present invention, a particle beam beam (FIG. 5) is extracted from an accelerator, which is a driver of particle beam gun therapy, for example, a fast repetitive induced acceleration synchrotron (Patent Document 2) with energy that continuously changes within one acceleration cycle. ) With respect to the gun target, the incident position and the incident angle are kept constant by the correction deflector within the acceleration cycle.

First, the bending angle of the irradiation particle beam on the line by the correction deflector is arbitrarily changed for each acceleration cycle, and the beam is fixed at the required irradiation position.

Next, the exciting current waveform of the correction deflector, which is a deflecting electromagnet excited at high speed, is made similar to the exciting current waveform of the main deflecting electromagnet of the accelerator. Therefore, the drive power supply circuit is connected to the correction deflector having the bipolar electromagnet cross section of FIG. 2 as shown in FIG. The configuration of the drive power supply circuit is a switching pulse power supply circuit that can be feedback-controlled within 100 msec as shown in FIG. Scanning can be freely realized in both positive and negative directions.

The capacitance is selected so that the product of the capacitance of the charging capacitor C and the inductance of the correction deflector satisfies a certain relationship with the excitation period of the deflecting electromagnet of the accelerator.

The maximum amplitude of the exciting current waveform of the correction deflector, including positive and negative signs, is changed for each acceleration cycle by an external control signal. The voltage for charging the capacitor C is arbitrarily adjusted by controlling the OFF timing of the charging thyristor Sc. Thyristor S0 and correction deflector forward current generation thyristors Sp1 and Sp2 are turned on at the timing when the correction deflector current is turned on, or correction deflector reverse current generation thyristors Sn1 and Sn2 are turned on to flow to the correction deflector. Change the direction of the current.

The circuit operation of FIG. 3 is as follows.
(A)
The charging thyristor Sc of the charging capacitor C is turned on to charge the charging capacitor C from the DC high-voltage power supply V0.

(B)
When the charging capacitor C reaches a predetermined voltage (determined by the control system that controls the entire beam irradiation), the charging thyristor Sc is turned off. If the charging thyristor Sc does not have a function to turn off by a trigger, the charging thyristor Sc is forcibly turned off by the attached circuit (S1 OFF cycle) surrounded by a broken line.

The forced OFF operation of the attached circuit (S1 OFF circuit) is as follows.
a. The ScOFF circuit thyristor S1 is turned on at the timing when the charging thyristor Sc is desired to be turned off.
b. The charging thyristor Sc is turned off by a reverse current. Further, the current flowing through the ScOFF circuit thyristor S1 becomes zero when the ScOFF circuit capacitor C1 is charged, and at that point, the ScOFF circuit thyristor S1 is turned off.
c. The charge discharge thyristor S2 is turned on, and the charge charged in the ScOFF circuit capacitor C1 is discharged through the C1 charge discharge resistor R1.
d. When the charge of the ScOFF circuit capacitor C1 becomes zero, the current flowing through the charge discharge thyristor S2 becomes zero, so that the C1 charge discharge thyristor S2 also turns off.
e. The above series of operations is completed by the time the charging thyristor Sc is turned on for charging the charging capacitor C.

(C)
The thyristor S0 and the thyristor for generating the forward current of the correction deflector are at the timing when the positive current (that is, the direction from top to bottom in the correction deflector in FIG. 3) is desired to flow through the correction deflector (the control system that controls the entire beam irradiation is determined). Sp1 and Sp2 are turned on at the same time. On the contrary, when it is desired to pass a negative current (that is, the direction from bottom to top at L in the figure), the thyristor S0 and the correction deflectors Sn1 and Sn2 for generating the reverse current are turned on at the same time.

(D)
The moment the voltage of the charging capacitor C decreases to zero potential, the thyristor S0 is turned off. After that, the current flowing through the correction deflector quickly becomes zero due to the critical attenuation resistor R.

(F)
This completes the periodic operation of the power supply circuit including the series of correction deflectors, and returns to (A) again.

Next, the results of simulating the extraction of the particle beam beam under 3D irradiation control based on the operating principle described in the circuit operation shown in FIG. 3 are shown below. However, the simulation time is for 4 cycles of the main bend magnet. In order to show that the corrected deflector current can freely change the peak value and the direction of the current for each accelerator cycle, the directions are positive, negative, positive, and positive from the first shot to the fourth shot, and the absolute value of the current is also It is changing in various ways.

FIG. 4 shows the exciting current waveform of the main deflection electromagnet. Due to the above-mentioned operation, the charging capacitor C becomes a charging voltage of various sizes as shown in FIG. 4 in the “voltage waveform of the charging capacitor” due to the OFF timing of the charging thyristor Sc. As shown in "Correction deflector exciting current waveform" of FIG. 4, whether the forward current generation thyristor (Sp1 & Sp2) is turned ON or the reverse current generation thyristor (Sn1 & Sn2) is turned ON at the timing when the correction deflector should be energized. The direction of the current and its absolute value can be changed freely.

In the case of FIG. 4, the current generation thyristor of [forward → reverse → forward → forward] is turned on for each accelerator cycle. However, the exciting current waveforms of all the exciting current waveforms are completely similar to the exciting current waveforms of the main deflection electromagnet during the time when the zero current is from zero to the peak current.

1 Feedback deflector system V0 DC high-voltage power supply Rc Charging resistance S1 ScOFF circuit thyristor C1 ScOFF circuit condenser S2 C1 Charge discharge thyristor R1 C1 Charge discharge resistance Sc Charging thyristor S0 Thyristor C Charging condenser D Critical attenuation diode R Resistance Sp1, Sp2 Compensation deflector Forward current generation thyristor Sn1, Sn2 Correction deflector Reverse current generation thyristor

Claims (2)

A correction deflector that corrects the irradiation position of the particle beam from the set value to the current position,
A drive power source that causes the correction deflector to form an exciting current waveform similar to the exciting current waveform of the main deflecting electromagnet in the time zone until the exciting current waveform of the main deflecting electromagnet of the accelerator that supplies the particle beam reaches the maximum value. Circuit and
A feedback deflector system characterized by consisting of. By the drive power supply circuit, the correction deflector
By generating a magnetic field strength that corrects the position of the gun target profile before the particle beam beam verification from the 3D dose profile of the gun target at the time of the previous particle beam beam irradiation.
The feedback deflector system according to claim 1, wherein the irradiation position of the particle beam is corrected from a set value to a current position.

Images