TW201822836A - Particle beam therapy apparatus - Google Patents

Abstract

In a particle beam therapy apparatus 100, a deflecting electromagnet 55 deflects an ion beam, and at the same time adjusts the magnetic intensity from a first magnetic field intensity higher than a target magnetic field intensity by main coils 2a and 2b to a second magnetic field intensity lower than the first magnetic field intensity and higher than the target magnetic field intensity by a predetermined amount, and thereafter compensates it to the target magnetic field intensity by compensation coils 3a and 3b that share magnetic cores 1a and 1b with the main coils 2a and 2b respectively. Thereby, the magnetic field of the deflecting electromagnet 55 is changed on the same hysteresis curve as in the case that the same energy is repeatedly delivered even if the beam energy is switched during the irradiation, and the same beam state as that at the adjustment can be realized even after the beam energy is changed.

Description

 Particle line therapy device  

The present invention relates to a particle beam therapy device for irradiating particle lines for cancer treatment.

In the conventional particle beam therapy apparatus, when the energy of the particle beam supplied to the irradiation system is switched, the so-called initialization process is performed, and the initialization process is repeated to set the minimum magnetic field strength after the excitation to the maximum magnetic field strength. The operation of re-excitation to the maximum magnetic field strength, after the initialization process, must be set by reducing the magnetic field from the maximum magnetic field strength. When this method is not used, a magnetic field different from the target will be generated even if the same current flows due to hysteresis.

For example, Patent Document 1 discloses a medical electronic acceleration device which is fixed at a desired value after saturation of a magnetic flux density of an electromagnet at each mounting, without being affected by hysteresis. The impact of changes.

 [Previous Technical Literature]    [Patent Literature]  

Patent Document 1: Japanese Patent Laid-Open No. Hei 3-236862 (page 2, right lower column, line 18 to page 3, upper left column, first line, third figure)

However, the initialization method shown in Patent Document 1 has a problem that it takes time to initialize. Further, when the magnetic field is lowered from the maximum magnetic field strength and the magnetic field strength is increased and corrected, the relationship between the magnetic field strength and the exciting current is not fixed to be unique, and there is a problem that it is difficult to ensure the accuracy of the magnetic field strength. Further, the magnitude of the deviation from the target magnetic field strength differs depending on the starting point, the size, and the increasing or decreasing direction of the change in the magnetic field strength. Therefore, it is necessary to create and store a large amount of setting data according to the mode of variation of the magnetic field strength, resulting in The problem of large cost increases.

The present invention has been made in an effort to solve the above problems, and an object of the invention is to provide a particle beam therapy apparatus capable of shortening a set time and achieving high-accuracy beam irradiation.

The particle beam therapy device of the present invention has a deflecting electromagnet that deflects the ion beam and supplies the ion beam to the illumination system. The magnetic field strength of the ion beam is higher than the target magnetic field by the main coil. The first magnetic field strength is adjusted to be lower than the first magnetic field strength and higher than the target magnetic field strength by a predetermined amount of the second magnetic field strength, and then corrected by the correction coil that shares the iron core with the main coil The strength of the magnetic field.

According to the present invention, by limiting the excitation of the correction coil of the common core to the direction of eliminating the excitation of the main coil, the same beam state can be maintained after the energy change, and the set time can be shortened and high precision can be achieved. Irradiation.

1‧‧‧ yoke

1a, 1b‧‧‧ pole core

2a, 2b‧‧‧ main coil

3a, 3b‧‧‧ correction coil

4‧‧‧beam catheter

10x, 10y‧‧‧ crosshairs

11‧‧‧beam position

41‧‧‧Particle line irradiation device

52‧‧‧Particle line generator

53‧‧‧Front accelerator

54‧‧‧Sync Accelerator

55‧‧‧ biased electromagnet

59‧‧‧beam irradiation system

100‧‧‧Particle line therapy device

D‧‧‧depth direction

S1, S2, ..., SN‧‧ tier

Fig. 1 is a view showing the configuration of a deflection electromagnet of the particle beam therapy apparatus according to the first embodiment of the present invention.

Fig. 2 is a view showing the overall configuration of a particle beam therapeutic apparatus according to a first embodiment of the present invention.

Fig. 3 is a view showing an example of the operation of the deflection electromagnet in the particle beam therapy apparatus according to the first embodiment of the present invention.

Fig. 4 is a view for explaining a method of adjusting a deflection electromagnet in the particle beam therapy apparatus according to the first embodiment of the present invention.

Fig. 5 is a view for explaining a method of adjusting a deflection electromagnet in a conventional particle beam therapy apparatus.

Fig. 6 is a view for explaining the operation of the deflecting electromagnet in the particle beam therapeutic apparatus according to the first embodiment of the present invention.

Fig. 7 is a view for explaining the operation of the deflection electromagnet in the conventional particle beam therapy apparatus.

Fig. 8 is a view showing an example of an irradiation region irradiated with energy adjusted by a deflection electromagnet of the particle beam therapy apparatus according to the first embodiment of the present invention.

Fig. 1 is a view showing a deflection electromagnet of a main configuration of a particle beam therapy device 100 according to a first embodiment of the present invention, wherein Fig. 1(a) shows a side view, and Fig. 1(b) shows a first figure (a). A cross-sectional view of the arrow in the direction of the AA line. Fig. 2 is a plan view showing a schematic configuration of the entire particle beam therapy device.

As shown in FIG. 2, the particle beam therapy apparatus 100 according to the first embodiment includes a particle beam generating device 52, a particle beam irradiation device 41, and a plurality of deflection electromagnets 55, and is connected via a beam delivery system 59. The particle beam generating device 52 includes an ion source front-stage accelerator 53 and a synchrotron 54. The charged particles (for example, proton ions or carbon ions) generated by the ion source are accelerated by the front accelerator 53 and are emitted from the front accelerator 53. The injection is made to the synchrotron 54. The particle line is accelerated by the synchrotron 54 and, after being increased to the set energy, is emitted from the exiting machine. The particle beam emitted from the synchrotron 54 passes through a plurality of deflecting electromagnets 55 and a beam transporting system 59 composed of a vacuum duct, and reaches the particle beam irradiation device 41, and is irradiated to the carrier from a particle beam irradiation nozzle (not shown). The affected part of the patient at the treatment station.

The deflecting electromagnet 55 biases the ion beam. The strength of the magnetic field required for deflection will vary depending on the beam energy. As shown in Fig. 1, the deflecting electromagnet 55 includes one pair of main coils 2a and 2b in a ring shape, and one pair of ring-shaped correction coils 3a and 3b disposed on the outer peripheral side of the main coils 2a and 2b. The pair of pole cores 1a and 1b on the inner peripheral side of the main coils 2a and 2b, and the beam guide 4 provided to bias the electromagnet 55 between the pair of pole cores 1a and 1b. The pair of pole cores 1a and 1b are made of a ferromagnetic body, and are integrally formed with the yoke 1 formed so as to surround the main coils 2a and 2b and the correction coils 3a and 3b.

The distance s from the patient to the electromagnet 55 closest to the patient is generally about 1 to 5 m from the irradiation site. The accuracy required for the beam position at the irradiation site is about ±0.5 mm. When s = 1 m is assumed, the error of the deflection angle of the deflection electromagnet 55 must be within ±0.5 mm rad. The deflecting electromagnet 55 generally deflects the orbit of the beam by a unit of several degrees or more. For example, if the deflection is 45 deg (=./4 rad), the magnetic field strength of the deflection electromagnet 55 must be controlled with an accuracy of ±0.5 mm rad/(./4 rad)*100=±0.06%.

Since it is difficult to ensure accuracy only by the main coils 2a and 2b, the deflection electromagnets 55 are generally provided with correction coils 3a and 3b that share the pole cores 1a and 1b with the main coils 2a and 2b, respectively. The deflection electromagnet 55 adjusts the excitation current of the correction coils 3a and 3b by using the beam orbit measurement results when only the main coils 2a and 2b are used, and reduces the track error to ensure accuracy. The adjustment is performed for each energy in a state in which the same energy is repeatedly delivered.

Fig. 3 is a view showing an example of a beam monitor before and after correction of the main coils 2a and 2b by the correction coils 3a and 3b in the deflection electromagnet 55. The cross lines 10x and 10y of Fig. 3 are the center lines of the vertical and horizontal directions centering on the designed beam position. In the case where the correction coils 3a, 3b are not used, the deflection electromagnet 55 is generally caused by a setting error of the machine, a manufacturing error, a magnetic field setting error, etc., which causes a deviation from the design of the beam trajectory. The upper beam position deviates from the beam position 11.

On the other hand, by using the correction coils 3a and 3b, the deflection electromagnet 55 can align the passing position of the beam on the monitor with the design according to the measurement results of the beam monitors disposed in the transport system and the illumination system. Thereby, the beam trajectory error of the entire conveying system and the illuminating system is reduced, and the beam position can be made into the designed beam position 12.

When the operation is performed under the same magnetic field strength, the adjustment methods by the main coils 2a and 2b and the correction coils 3a and 3b are not limited, but the magnetic field strength is changed and the electromagnet 55 has the magnetic pole cores 1a and 1b. The hysteresis must be considered.

Fig. 4 is a view for explaining an adjustment method when the magnetic field strength of the electromagnet 55 is changed in the particle beam therapy apparatus 100 according to the first embodiment of the present invention. Fig. 4(a) shows the change of the exciting current, and Fig. 4(b) shows the relationship between the hysteresis loop and the exciting current. Fig. 5 is a view showing a method of adjusting a conventional deflection electromagnet corresponding to Fig. 4; The chain lines of Figs. 4(b) and 5(b) show the case where the core is excited from the demagnetized state, and the broken line shows the general hysteresis curve. Since the biasing electromagnet is generally a unipolar power source, it operates as a solid line.

In the conventional particle beam therapy apparatus, in order to avoid the influence of hysteresis to ensure the accuracy of the magnetic field, the following method is employed: the so-called initialization process is performed, and the initialization process is repeated: after the excitation to the maximum magnetic field strength, The operation of setting the minimum magnetic field strength and re-energizing to the maximum magnetic field strength; and reducing the magnetic field from the maximum magnetic field strength to the predetermined magnetic field strength after the initialization process. The processing of initialization is performed one to several times. Since the change of the beam energy is performed from high energy to low energy, there is no problem in biasing the main coil of the electromagnet, but the correction coil is excited after the adjustment of the main coil, as shown in Fig. 5. (a) When the magnetic field strength is corrected in the direction of improvement (I _2U → I _3U ), as shown in Fig. 5 (b), the change in magnetic field strength with respect to the excitation current due to hysteresis is from I ₁ to The hysteresis curve between I ₀ deviates, and the excitation current corresponding to the target value _{Bob of the} magnetic field strength deviates. Therefore, when the beam energy is changed without initializing, even if the excitation current adjusted in the state in which the same energy is repeatedly supplied is set, the magnetic field does not become the state at the time of adjustment, and the beam state after the energy change does not occur. The situation of the desired beam state.

In the particle beam therapy system 100 according to the first embodiment of the present invention, the deflecting electromagnet 55 biases the ion beam, and the main coil 2a, 2b increases the magnetic field strength from the first magnetic field strength which is higher than the target magnetic field strength. After being adjusted to be lower than the first magnetic field strength and higher than the target magnetic field strength by a predetermined amount of the second magnetic field strength, the correction coils of the magnetic pole cores 1a, 1b are shared by the main coils 2a, 2b, respectively. The ion beams corrected to the magnetic field strength of the target are supplied to the illumination system by 3a and 3b.

Deflecting electromagnet 55 is changed based upon the magnetic field strength, as in FIG. 4 (a), the excitation to the saturation based upon the maximum magnetic field strength (I _1), the exciting current of the main coil 2a, 2b than the magnetic field strength becomes The target value _Bob is raised by a predetermined amount (I ₂ ), and the excitation current of the correction coils 3a and 3b is corrected (I ₂ → I ₃ ) such that the magnetic field strength due to the main coils 2a and 2b is lowered. As shown in Fig. 4(b), the target value _Bob of the magnetic field strength is set on the hysteresis curve between I ₁ and I ₀ . Here, the predetermined amount is a value corresponding to a range within 1% of the maximum output of the deflection electromagnet 55.

In this manner, the excitation of the correction coils 3a and 3b sharing the magnetic pole cores 1a and 1b with the main coils 2a and 2b is limited to the direction in which the excitation of the main coils 2a and 2b is canceled, and the energy is switched even during the irradiation. In the case where the same energy is repeatedly transmitted, the magnetic field is changed on the same hysteresis curve. Therefore, the difference between the energy change and the adjustment can be reduced, and the same beam state can be maintained after the energy change.

Next, the operation of the deflecting electromagnet 55 in the particle beam therapy device 100 according to the first embodiment of the present invention will be described. Fig. 6 is a view for explaining an adjustment method when the magnetic field strength of the electromagnet 55 is continuously changed plural times in the particle beam therapy device 100 according to the first embodiment of the present invention. Fig. 6(a) shows the change of the exciting current, and Fig. 6(b) shows the relationship between the hysteresis loop and the exciting current. Fig. 7 is a view showing an adjustment method in the case of the conventional deflection electromagnet corresponding to Fig. 6. Fig. 8 is a view showing an example of an irradiation region to be irradiated by the energy adjusted by the electromagnet 55 in the particle beam therapy device 100 according to the first embodiment of the present invention.

As shown in Fig. 8, in the conventional particle beam irradiation apparatus using a laminated original irradiation method or a scanning irradiation method, the layers S1, S2, ..., SN (N is an integer) with respect to the depth direction D are used. When the method is divided and the irradiation area is irradiated, it is necessary to change the energy of the beam irradiated to the patient. When the energy of the beam is changed by the particle beam generating device 52 or the beam transporting system 59, the intensity of the magnetic field biased toward the electromagnet 55 must also be changed in accordance with the energy of the beam. In this way, when the magnetic field strength is to be changed plural times, the method of performing the following operations in accordance with the irradiation of each layer is performed by performing a so-called initialization process, which is repeated after the excitation to the maximum magnetic field strength. The operation is set to the lowest magnetic field strength and then excited to the maximum magnetic field strength, and after the initialization process, the magnetic field is set from the maximum magnetic field strength to a predetermined magnetic field strength, and is again excited to the maximum magnetic field strength after the irradiation. The initialization time usually takes about 1 minute, and there is a problem of efficiency in setting time.

Furthermore, as shown in Fig. 7, the magnetic field is first excited to the maximum magnetic field strength (I ₁ ), and then decreased to a predetermined magnetic field strength (I ₂ ) and then corrected in the direction of increasing the magnetic field strength (I ₂ → I ₃ ). After the irradiation, the energy is changed without initializing, and there is no setting method of the subsequent excitation current. The relationship between the excitation current and the magnetic field strength deviates from the hysteresis curve between I ₁ and I ₀ (I ₃ → I ₄ →I ₅ →I ₆ →I ₇ ), even if the excitation current is adjusted so that the same energy is repeatedly supplied, it does not become the magnetic field strength at the time of adjustment.

In the particle beam therapy apparatus 100 according to the first embodiment of the present invention, the deflecting electromagnet 55 is first set to the main coil 2a after being excited to the maximum magnetic field strength (I ₁ ) of saturation as shown in Fig. 6(a). The excitation current of 2b is higher than the target value B _{ob1 of the} magnetic field strength by a predetermined amount (I ₂ ), and the excitation current of the correction coils 3a and 3b is made such that the magnetic field strength due to the main coils 2a and 2b is lowered. Correction (I ₂ → I ₃ ). At this time, as shown in Figure section 6 (b), the target value of magnetic field strength B _ob1 is set based on the I ₁ to I ₀ of the hysteresis curve. In this state, the beam system supplied to the particle beam irradiation device 41 by the beam irradiation system 59 including the deflection electromagnet 55 is irradiated to the layer S1 shown in Fig. 8.

Next, as shown in Fig. 6(a), the deflection electromagnet 55 is set so that the excitation current of the main coils 2a and 2b becomes a target value of the magnetic field strength in a state (I ₃ ) in which the layer S1 is irradiated. B _{ob2 is raised} by a predetermined amount (I ₄ ), and the excitation currents of the correction coils 3a and 3b are corrected (I ₄ → I ₅ ) so that the magnetic field strength due to the main coils 2a and 2b is lowered. At this time, as shown in Figure section 6 (b), the target value of magnetic field strength B _ob2 is set based on the I ₁ to I ₀ of the hysteresis curve. In this state, the beam system supplied to the particle beam irradiation device 41 by the beam irradiation system 59 including the deflection electromagnet 55 is irradiated to the layer S2 shown in Fig. 8.

Next, as shown in Fig. 6(a), the deflection electromagnet 55 is set so that the excitation current of the main coils 2a and 2b becomes a target value of the magnetic field strength in a state (I ₃ ) in which the layer S2 is irradiated. B _{ob3 is raised} by a predetermined amount (I ₆ ), and the excitation currents of the correction coils 3a and 3b are corrected (I ₆ → I ₇ ) such that the magnetic field strength due to the main coils 2a and 2b is lowered. At this time, as shown in Figure section 6 (b), the target value of magnetic field strength _B ob3 based on I ₁ is set to I ₀ of the hysteresis curve. In this state, the beam system supplied to the particle beam irradiation device 41 by the beam irradiation system 59 including the deflection electromagnet 55 is irradiated to the layer S3 shown in Fig. 8. Further, the predetermined amounts are all values corresponding to a range within 1% of the maximum output of the deflecting electromagnet 55.

In this manner, the excitation of the correction coils 3a and 3b sharing the magnetic pole cores 1a and 1b with the main coils 2a and 2b is limited to the direction in which the excitation of the main coils 2a and 2b is canceled, and the energy is continuously switched even during the irradiation. In the case of the magnetic hysteresis curve which is the same as the case where the same energy is repeatedly transmitted, the magnetic field can be changed. Therefore, it is not necessary to initialize each energy change, thereby reducing the difference between the energy change and the adjustment, and after the energy change. It is also possible to maintain the same beam state as when adjusting.

As described above, the deflecting electromagnet 55 of the particle beam therapy apparatus 100 according to the first embodiment of the present invention biases the ion beam, and the magnetic field strength is higher than the target magnetic field by the main coils 2a and 2b. The magnetic field strength is adjusted to be lower than the first magnetic field strength and higher than the target magnetic field strength by a predetermined amount of the second magnetic field strength, and the magnetic pole cores 1a, 1b are shared by the main coils 2a, 2b, respectively. By correcting the coils 3a and 3b and correcting the ion beam as the target magnetic field strength to be supplied to the illumination system, the excitation of the correction coil of the common core is limited to the direction in which the excitation of the main coil is canceled, even if it is irradiated. In the case of switching energy, the magnetic field can be changed on the same hysteresis curve as the case of repeatedly delivering the same energy, so that the difference between the energy change and the adjustment can be reduced, and the same shot can be maintained after the energy change. Beam status.

Furthermore, even when the energy is continuously switched during the irradiation, the magnetic field can be changed on the hysteresis curve which is the same as the case where the same energy is repeatedly supplied, so that the energy can be reduced without initializing each time the energy is changed. The difference between the change and the adjustment time, and the same beam state as the adjustment can be maintained after the energy change. Further, the setting data of the combination of the change start point, the change amount, and the energy to be changed for each energy is not required, that is, the setting data for adjustment without changing the beam energy can be applied. Thereby, the set time can be shortened, and the setting data of the deflection electromagnet that is biased toward the electromagnet can be minimized by any combination of the excitation currents adjusted for each energy, and the deflection electromagnet can be made the same as the adjustment time. In this state, the beam state can be made the same as in the adjustment, and high-accuracy beam irradiation can be realized.

Further, the present invention is applicable to at least one biasing electromagnet in a particle beam therapy device. Further, the present invention can be modified and omitted as appropriate within the scope of the invention.

Claims (3)

 A particle beam therapy device having a deflecting electromagnet that deflects an ion beam and supplies an ion beam to an illumination system, the magnetic field strength of the ion beam being higher than a target magnetic field by the main coil The first magnetic field strength is adjusted to be lower than the first magnetic field strength and higher than the target magnetic field strength by a predetermined amount of the second magnetic field strength, and then corrected by the correction coil that shares the iron core with the main coil The strength of the magnetic field.    The particle beam therapy apparatus according to claim 1, wherein the predetermined amount is a value corresponding to a range within 1% of a maximum output of the deflection electromagnet.    The particle beam therapy apparatus according to the first or second aspect of the invention, wherein the adjustment and the correction are performed repeatedly each time the magnetic field intensity of the deflection electromagnet is changed to the target magnetic field strength.