1. Field of the Invention
The present invention relates to a charged-particle beam accelerator which emits a high-energy particle beam produced by accelerating along a circulating orbit a low-energy beam introduced from an ion source, as well as a particle beam radiation therapy system employing such a charged-particle beam accelerator and a method of operating the particle beam radiation therapy system.
2. Description of the Background Art
Conventionally, charged-particle beams produced by circular accelerators like a synchrotron are used for physical experiments and medical applications. The circular accelerator generates a particle beam by accelerating charged particles along a circulating orbit. The charged-particle beam is taken out of the circulating orbit and delivered to a location where the beam is used for a physical experiment or medical treatment through a beam transport line. In one beam extraction technique employed in the circular accelerator, a high-frequency electric field is applied to a circulating beam to increase the amplitude of betatron oscillation up to a point where the betatron oscillation exceeds a stability limit and the charged-particle beam is extracted to the exterior, in which beam extraction is started and stopped by turning on and off the high-frequency electric field.
One example of this kind of approach is identified in Japanese Examined Patent Publication No. 2596292. Although this Patent Publication proposes a beam extraction method for extracting a charged-particle beam from an accelerator by applying a high-frequency electromagnetic field to the circulating beam to increase the amplitude of betatron oscillation, the Publication does not disclose any practical method of frequency control for radio frequency knockout (RF-KO).
Another example of a prior art approach is found in Japanese Examined Patent Publication No. 2833602 which discloses a charged-particle beam radiation system including a beam deflector, in which a charged-particle beam is extracted by using the beam extraction method of Japanese Examined Patent Publication No. 2596292. The beam deflector steers the beam to irradiate a desired spot with charged particles extracted by the aforementioned beam extraction method. Emission of charged particles is once stopped and resumed with the beam directed to a next spot of irradiation by the beam deflector by using the same extraction method. This process is repeated as many times as necessary.
A non-patent document titled “PROGRESS OF RF-KNOCKOUT EXTRACTION FOR ION THERAPY” published in the Proceedings of the European Particle Accelerator Conference (EPAC 2002), pp. 2739-2741, describes a technique for realizing high-speed beam extraction and cut-off operation with a uniform intensity of the extracted beam over time based on the beam extraction method of Japanese Examined Patent Publication No. 2596292.
Another non-patent document titled “Fast beam cut-off method in RF-knockout extraction for spot-scanning” published in Nuclear Instruments and Methods in Physics Research Section A, Volume 489 (2002), pp. 59-67, gives a more detailed description of the technique introduced in the aforementioned non-patent document titled “PROGRESS OF RF-KNOCKOUT EXTRACTION FOR ION THERAPY.”
Still another non-patent document titled “Advanced RF-KO slow-extraction method for the reduction of spill ripple” published in Nuclear Instruments and Methods in Physics Research Section A, Volume 492 (2002), pp. 253-263, provides a detailed description of a system control method.
According to the non-patent documents cited above describing a practical method of realizing the aforementioned charged-particle beam radiation system of Japanese Examined Patent Publication Nos. 2833602 and 2596292, three function generators are needed for generating high-frequency electric fields and it is necessary to control these three function generators as well as a high-frequency accelerator, in which transverse and longitudinal RF fields are turned on and off, for performing beam extraction and cut-off operation. This requires a complicated control system which results in an expensive beam radiation system, also causing a problem concerning equipment reliability which is most important for medical systems.
A synchrotron used in the charged-particle beam radiation system must radiate a charged-particle beam at varying energy levels and beam intensities. To radiate the charged-particle beam at a desired energy level and beam intensity, it is necessary to optimally control different beam parameters according to all possible conditions. Therefore, optimization of the parameters at construction and adjustment of the charged-particle beam radiation system is so time-consuming that the system becomes considerably costly.
The aforementioned non-patent documents propose arrangements employing a power supply for electromagnets having extremely high stability so that these arrangements do not cause any stability-related problem. If the stability of the power supply is lowered for the sake of cost reduction, however, resultant fluctuation in power supply voltage will cause limits of a stability region to fluctuate. Therefore, even if the charged-particle beam radiation system is entirely turned off, a beam will be emitted afterwards due to the power supply voltage fluctuation and this poses a serious problem.
The present invention is intended to provide a solution to the aforementioned problems of the prior art. Accordingly, it is a specific object of the invention to provide a charged-particle beam accelerator which makes it possible to simplify beam extraction control, realize increased reliability, reduce the number of constituent hardware elements, permit the presence of a wide range of ripples contained in currents supplied from power supplies for electromagnets, and achieve an eventual cost reduction. It is another specific object of the invention to provide a particle beam radiation therapy system employing such a charged-particle beam accelerator and a method of operating the particle beam radiation therapy system.
According to the invention, a charged-particle beam accelerator includes means for accelerating a charged-particle beam and circulating the charged-particle beam along an orbiting path, means for causing betatron oscillation of charged particles in a resonating state outside a stable region of resonance, means for increasing the amplitude of the betatron oscillation of the charged-particle beam within the stable region of resonance, and means for varying the stable region of resonance. In this charged-particle beam accelerator, the aforesaid means for increasing the amplitude of the betatron oscillation is controllably operated within a frequency range in which the circulating beam does not go beyond a boundary of the stable region of resonance, and the aforesaid means for varying the stable region of resonance is controllably operated with appropriate timing as required for beam extraction so that the charged-particle beam is extracted with desired timing.
The charged-particle beam accelerator of the invention includes a limited number of elements which should be controlled when extracting the charged-particle beam. The charged-particle beam accelerator makes it possible to continuously extract the charged-particle beam with a capability to initiate and terminate beam extraction by simple control operation. Even if an output of each electromagnet power supply contains a large ripple component, it is possible to prevent beam extraction from occurring with undesirable timing. As a whole, the charged-particle beam accelerator of the invention enables a system size reduction, an improvement in reliability and an overall cost reduction.
These and other objects, features and advantages of the invention will become more apparent upon reading the following detailed description in conjunction with the accompanying drawings.
A first embodiment of the invention is now described with reference to the accompanying drawings.
A charged-particle beam extracted from the charged-particle beam accelerator 200 through the extraction septum 10 thereof is guided through a beam transport line 300 to an irradiation apparatus 400 provided in a treatment room. The charged-particle beam is ejected from a beam delivery unit 17 of the irradiation apparatus 400 toward an irradiation target, such as an affected part of the abdomen of a patient 30. The beam transport line 300 includes a bending electromagnet unit 20, a beam monitor 15, a beam blocking electromagnet unit 18, a beam damper 19 and a beam path bending electromagnet unit 16. While the beam path bending electromagnet unit 16 constitutes part of the beam transport line 300 in this embodiment, the beam path bending electromagnet unit 16 may be included in the irradiation apparatus 400.
The irradiation apparatus 400 includes a target displacement sensor 31 for detecting displacements of the irradiation target due to respiration of the patient 30 in addition to the beam delivery unit 17.
Now, operation of the charged-particle beam accelerator 200 of the first embodiment is discussed.
The charged-particle beam accelerated by the charged-particle beam accelerator 200 is an ion beam emitted from the ion source 1. The linear accelerator 2 accelerates the ion beam emitted from the ion source 1 up to an injection energy level necessary for operating a synchrotron (i.e., the charged-particle beam accelerator 200). The ion beam injected through the injection septum 3 is guided by the main bending electromagnet units 4 to travel along a circulating path of the charged-particle beam accelerator 200. As each of the main quadrupole electromagnet units 5 applies a beam focusing force to the ion beam, the ion beam continues to travel along the circulating path without any increase in beam size (beam diameter) In this embodiment, the main bending electromagnet units 4 and the main quadrupole electromagnet units 5 are arranged in four combinations (each including one each main bending electromagnet unit 4 and main quadrupole electromagnet unit 5). Although two kinds of quadrupole electromagnet units having different polarities are normally used for horizontal and vertical focusing of the beam in the synchrotron, the main bending electromagnet units 4 of this embodiment are bending electromagnet units which serves a function of applying a beam focusing force acting in a vertical direction as well by generating magnetic fields of which intensities vary in radial directions or by having edge angles. Therefore, the main quadrupole electromagnet units 5 used in the charged-particle beam accelerator 200 are of a single kind. Theoretically, each of the main bending electromagnet units 4 applies a bending force and a horizontal focusing force to the beam at the same time.
While the injected beam is accelerated by the high-frequency acceleration unit 6, the intensities of magnetic fields generated by the main bending electromagnet units 4 and the main quadrupole electromagnet units 5 are increased with an increase in beam energy (momentum) so that a beam circulating orbit formed in the charged-particle beam accelerator 200 would not fluctuate. Upon completion of acceleration, the intensities of the magnetic fields generated by the main bending electromagnet units 4 and the main quadrupole electromagnet units 5 are kept constant, and the high-frequency acceleration unit 6 is deactivated or the high-frequency acceleration unit 6, if left activated, is operated at a phase where the beam is not further accelerated or decelerated. Consequently, the beam continues to orbit with a constant energy.
Here, the behavior of each single particle (ion) is simply explained before proceeding to a discussion of beam extraction. The particle travels along the beam circulating orbit while oscillating around a central orbiting axis with the aid of the focusing forces exerted by the main bending electromagnet units 4 and the main quadrupole electromagnet units 5. This oscillation of the particle is referred to as betatron oscillation. If the value of a fractional part of the number of betatron oscillations per circulation along the circulating orbit is zero, ½ or ⅓ (or 1⅓), the orbiting particle is brought into a resonating state due to a magnetic field error. In this condition, the amplitude of betatron oscillation increases and the particle in the resonating state collides with an inner wall of a vacuum chamber, for example, and eventually disappears. Resonances which occur when the value of the fractional part of the number of betatron oscillations per circulation is zero, ½ and ⅓ are referred to as a first-order resonance, a ½ (second-order) resonance and a ⅓ (third-order) resonance, respectively. Although resonances occur due to magnetic field errors also when the fractional part of the number of betatron oscillations per circulation is ¼, ⅕ and so on, particular attention should be given to the ⅓ (third-order) and lower order resonances. If the fractional part of the number of betatron oscillations per circulation deviates far from these values, each particle moves inside an ellipse shown in
Now, a process of beam extraction is discussed. The betatron oscillation in a horizontal direction is controlled to approach the ⅓ resonance by varying magnetic fields generated by the main quadrupole electromagnet units 5 and, typically, the sextupole electromagnet unit 7 is excited to make it easier to create a resonating state. A region in which a beam can circulate in a stable manner without a further enhancement of the betatron oscillation is referred to as “acceptance.” Due to nonlinearity of sextupole magnetic fields, the acceptance takes a triangular shape as shown in
The prior art arrangements of the earlier-mentioned Patent Publications and non-patent documents employ a method of shifting particles to the outside of a separatrix by increasing the amplitude of betatron oscillation with the aid of a high-frequency electric field while keeping the size of the separatrix constant. A device used in these prior art arrangements for generating the high-frequency electric field corresponds to the RF-KO unit 8 of the first embodiment shown in
The beam extraction process described above is conventional. A beam extraction process of this embodiment is discussed in the following. The extraction quadrupole electromagnet unit 9 shown in
As the high-frequency electric field is used only for spreading the beam, only one RF-KO unit (radio frequency generating unit) 8 is required for beam extraction. Since the number of betatron oscillations per circulation differs from one particle to another and from one amplitude to another, there exist many orbiting particles which can not be taken out with a single-frequency electric field. Therefore, it is desirable to apply a conventionally used frequency-modulated high-frequency electric field, wherein the modulation factor should be set to a value at which the beam is not directly extracted but the particles orbiting near the center of the separatrix are spread outward. Application of a conventionally used frequency-modulated high-frequency electric field is also effective. The RF-KO unit 8 of the embodiment produces similar advantageous effects on high-frequency magnetic fields as well.
The extracted particle beam is guided to the treatment room through the beam transport line 300 and projected on the patient 30 through the beam delivery unit 17. The beam delivery unit 17 includes parallel scanning electromagnets 21 for targeting the beam to desired locations, a dose monitor, a beam position monitor and a range shifter 22 for varying the beam energy.
Here, an example of a treatment by spot-scanning irradiation is described with reference to
A few tens of milliseconds is needed for varying magnetic fields generated by the scanning electromagnets 21 and the range shifter 22 requires a switching time of approximately 30 ms for changing its thickness. Accordingly, the spot-scanning irradiation is executed as follows. Specifically, the scanning electromagnets 21 direct the beam axis to a first irradiation spot by moving the beam axis along the radial scanning direction as necessary. Next, the range shifter 22 sets the beam to target a desired irradiation depth (target depth). Then, the scanning electromagnets 21 direct the beam axis to a next irradiation spot by moving the beam axis along the radial scanning direction and the range shifter 22 switches its thickness for a next irradiation depth. This sequence is repeatedly executed as many times as necessary. When all irradiation spots taken along one radial scanning direction have been irradiated at all target depths with the particle beam, the scanning electromagnets 21 are rotated to emit the beam against irradiation spots taken along a next radial scanning direction. Irradiation time per spot ranges from a few milliseconds to a few tens of milliseconds. The particle beam is extracted from the synchrotron 200 and ejected through the beam delivery unit 17 when all preparatory operations for radiating the beam against each irradiation spot have been completed. As the total number of irradiation spots could reach a few thousands or more, it is needed to extract the beam from the synchrotron 200 as soon as the preparatory operations for irradiation have been completed.
When irradiating an organ which greatly moves due to respiration of the patient 30, such as a lung or liver, the beam is ejected when the organ is relatively stabilized during an exhaling period. This approach helps reduce unwanted dose to any normal (unaffected) tissues. One method for achieving efficient irradiation is to detect target area displacements of the abdomen of patient 30 due to respiration by using the target displacement sensor 31 which can remotely detect displacements of an abdominal part where an irradiation target exists and to emit the beam when the level of a signal output from the target displacement sensor 31 falls within a preset range. An irradiation enable signal shown in
It is needless to mention that a relationship between movements of the abdomen of patient 30 due to respiration and the location of the organ to be treated must be determined beforehand through measurements by magnetic resonance imaging (MRI) or computerized tomography (CT) scans.
An example of an operating pattern of the synchrotron 200 is now described with reference to
Shown in
The aforementioned extraction and radiation method of this embodiment can be advantageously used not only for medical applications but also for physical experiments. When used in a physical experiment, the synchrotron 200 produces accelerated particles which are caused to strike against a target. Collision of the particles against the target creates secondary and tertiary particles which are detected by a sensor. If too many particles are struck at once against the target, the sensor will be saturated with secondary and tertiary particle emissions. The extraction and radiation method of the embodiment can be used for successively extracting and emitting particle beams in controlled quantities, thereby preventing such a saturation problem, for instance. According to this method of the embodiment, it is possible to carry out measurements in an efficient fashion when appropriate timing for extracting and emitting particle beams has been determined.
The aforementioned arrangement of the first embodiment is advantageous in that the charged-particle beam accelerator 200 can be easily controlled with a least number of devices needed for controlling beam extraction.
A second embodiment of the invention is now described. While the RF-KO unit (radio frequency generating unit) 8 is turned off when the extraction quadrupole electromagnet unit 9 is activated in the foregoing first embodiment as can be seen from
While
It is advantageous to gradually increase the amplitude of the output signal of the frequency generating device 8 with time. This is because the density of the particle beams in the proximity of the stability limit of resonance can be made nearly constant by doing so. Although this amplitude variation of the output signal (amplitude modulation) typically includes both a first mode of amplitude modulation repetitively performed in synchronism with recurring cycles of frequency modulation and a second mode of amplitude modulation performed over a period during which all of accelerated particles are extracted, the output signal of the frequency generating device 8 may be amplitude-modulated by only the second mode of amplitude modulation.
While magnetic field waveforms generated by the extraction quadrupole electromagnet unit 9 shown in
Although there is a possibility that the extracted beam intensity varies due to a relationship between the phase of the FM signal generated by the frequency generating device 8 and activation timing of the extraction quadrupole electromagnet unit 9 in the second embodiment, the aforementioned arrangement of the second embodiment is advantageous in that the number of devices of which operating timing must be controlled decreases, making it easier to control system operation.
While the frequency generating device 8 is continuously operated regardless of the irradiation enable signal as shown in
A third embodiment of the invention is now described. It is advantageous to install the beam blocking electromagnet unit 18 for generating a magnetic field only during a period between the extraction start signal (
A fourth embodiment of the invention is now described. While the magnetic field generated by the extraction quadrupole electromagnet unit 9 has a triangular waveform in the first embodiment as shown in
A fifth embodiment of the invention is now described. Although the foregoing discussion of the first to fourth embodiments does not mention any details of operation and control of the high-frequency acceleration unit 6 during irradiation treatment, the high-frequency acceleration unit 6 may be operated in synchronism with the RF-KO unit (radio frequency generating unit) 8. An advantage of synchronizing the high-frequency acceleration unit 6 with the radio frequency generating unit 8 is that this operation method makes it possible to extract the particle beam at a uniform intensity over time with a minimum amount of spike noise.
Since a maximum value of the variable range Δp of the momentum p in the betatron oscillation is determined by the strength of the electric field generated by the high-frequency acceleration unit 6, the strength of this electric field is set to a value at which the orbiting particles would not go to the outside of the separatrix.
Now, a specific example of a high-frequency acceleration system is described. Generally, it is necessary in a particle beam synchrotron that power supplies of electromagnets and a high-frequency acceleration unit be precisely synchronized in operating pattern during acceleration and the operating pattern of the high-frequency acceleration unit be varied in a complex manner. For this purpose, the particle beam synchrotron includes a memory for storing a plurality of operating patterns which are successively output and amplified by a high-frequency amplifier. These operating patterns are optimized through beam emission tests, for instance. One alternative to this memory-assisted method would be to add varying operating patterns as shown in
A sixth embodiment of the invention is now described. Shown in
A seventh embodiment of the invention is now described. In this embodiment, the charged-particle beam accelerator 200 can be operated at a chromaticy set to a value close to zero by adjusting the sextupole electromagnet unit 7. In this case, the stability limit of resonance becomes almost unchanged regardless of the value of Δp/p of each particle in Steinbach diagrams shown in
A control method for interrupting emission of the particle beam in the beam transport line 300 according to an eighth embodiment of the invention is now described. When it is required for the extraction quadrupole electromagnet unit 9 to generate a strong magnetic field, the inductance of the extraction quadrupole electromagnet unit 9 becomes so large that it becomes difficult to control beam irradiation and, as a consequence, there can occur a case where a sufficient period of time is not available for the extraction quadrupole electromagnet unit 9 as required by characteristics thereof to stop beam irradiation after receiving the dose complete signal. In such a case, it becomes possible to quickly stop beam irradiation if a high-speed pulse-driven electromagnet unit (irradiation beam controlling electromagnet unit) 25 is disposed in the beam transport line 300 as shown in an overall system diagram of
Although the extracted particle beam arrives at the irradiation beam controlling electromagnet unit 25 with a slight lag from the extraction start signal, the particle beam can be emitted with proper timing if ON timing of the irradiation beam controlling electromagnet unit 25 is delayed from the extraction start signal.
In this embodiment, the high-frequency acceleration unit 6 and the RF-KO unit 8 are operated in the same way as in the first embodiment. The eighth embodiment makes it possible to quickly interrupt irradiation and prevent the particle beam from being transported to the beam delivery unit 17 during periods when irradiation is not to be made.
Described below is a ninth embodiment of the invention which provides an arrangement for operating the synchrotron 200 taking into consideration ripples contained in currents supplied from the power supplies of the main bending electromagnet units 4 and the main quadrupole electromagnet units 5, for example. Ripple components, or fluctuations, in the output currents of the power supplies of the main bending electromagnet units 4 and the main quadrupole electromagnet units 5 of the synchrotron 200 can cause fluctuations of the size of the separatrix. For example, the separatrix size varies as shown by shaded areas (a) and (b) in
To prevent this inconvenience, the FM modulation factor of the high-frequency electric field generated by the RF-KO unit 8 and the strength of the electric field generated by the high-frequency acceleration unit 6 are determined in consideration of the fluctuation of the separatrix size caused by the power supply ripple components. This approach makes it possible to keep spreading of the particle beam within limits in which the separatrix is at the minimum size in the presence of the ripple components.
It is supposed that the aforementioned problem associated with the power supply ripple components does not normally occur in conventional synchrotrons as extremely stable power supplies are used therein. The aforementioned arrangement of the ninth embodiment is advantageous in that the synchrotron 200 can employ power supplies having a relatively low stability, resulting in an overall cost reduction.
A tenth embodiment of the invention is now described. While the extraction quadrupole electromagnet unit 9 is used for reducing the separatrix size in the foregoing first to ninth embodiments, the high-frequency acceleration unit 6 can produce the same effects as the extraction quadrupole electromagnet unit 9. In the Steinbach diagrams shown in
A method of operating the particle beam radiation therapy system according to the eleventh embodiment of the invention is now described. In the aforementioned first embodiment, the synchrotron 200 is run in the operating pattern in which the circulating beam is decelerated at a point in time when the beam has reached a level equal to or lower than the preset intensity level. If the irradiation target is a human body and the intensity of the circulating beam in the synchrotron 200 is not high enough upon completion of irradiation during one respiratory cycle to irradiate the target in succession over a permissible irradiation time in a succeeding respiratory cycle, for example, the synchrotron 200 should preferably be run in an operating pattern including deceleration, reinjection and acceleration. This operating pattern is advantageous in reducing loss of time. There can be various cases where the synchrotron 200 is to be run in the operating pattern including deceleration, reinjection and acceleration. For example, this operating pattern may be used in a case where the circulating beam intensity is just high enough to irradiate an intended target spot for only half or less of an average value of previously measured permissible irradiation times. The synchrotron operating pattern of the eleventh embodiment makes it possible to reduce loss of time and shorten a total irradiation time.
A twelfth embodiment of the invention is now described. The foregoing discussion of the first embodiment has illustrated the spot-scanning irradiation based on the parallel scanning method using the parallel scanning electromagnets 21 with reference to
A thirteenth embodiment of the invention is now described. While the aforementioned synchronization approach of the twelfth embodiment is intended for use in the spot-scanning irradiation based on the parallel scanning method, this approach of the twelfth embodiment can produce the same advantageous effects when applied to an ordinary spot-scanning irradiation method as well.
The aforementioned approach of the thirteenth embodiment is applicable to other type of spot-scanning irradiation than the parallel scanning method as discussed above.
A fourteenth embodiment of the invention is now described. While the particle beam is continuously extracted and radiated during an irradiation time of each target spot in the foregoing embodiments, the invention is not limited thereto. The value of required dose varies from one irradiation spot to another. In this embodiment, the RF-KO unit 8 and the extraction quadrupole electromagnet unit 9 are alternately operated to output a pulse beam for a period equal to or shorter than an irradiation time which gives a minimum dose to one irradiation spot. For example, at least one of the RF-KO unit 8 and the extraction quadrupole electromagnet unit 9 is deactivated when the required dose has been fulfilled, and then, both the RF-KO unit 8 and the extraction quadrupole electromagnet unit 9 are activated again when preparatory operations for irradiating a next target spot have been completed. A prescribed dose is given to each irradiation spot by repeating the aforementioned ON and OFF sequence. Each beam extraction period is used as a period required for the spreading of the beam by the RF-KO unit 8. It is also advantageous to use the high-frequency acceleration unit 6 as in the aforementioned fifth embodiment.
The fourteenth embodiment is advantageous in that it allows for easy control of the synchrotron 200 and extraction of the beam can be completely interrupted during periods between successive irradiation cycles as all system components related to beam extraction are deactivated during those periods.
A fifteenth embodiment of the invention is now described. While the foregoing embodiments have been discussed as being applied to the particle beam radiation therapy system employing the scanning irradiation method, the invention is also applicable to a system employing an ordinary broad beam method. The broad beam method is a method of broadening the beam by use of a scatterer or a wobbler electromagnet yet reducing irradiation of areas other than the affected body part of the patient 30 to be treated.
At a point in time when it becomes possible to irradiate the affected part of the patient 30, the synchrotron 200 begins to alternately operate the RF-KO unit 8 and the extraction quadrupole electromagnet unit 9 to intermittently output the particle beam. Upon receiving a command signal for interrupting the beam from an irradiation control system, the synchrotron 200 terminates extraction of the beam by deactivating at least one of the RF-KO unit 8 and the extraction quadrupole electromagnet unit 9. As discussed in the foregoing fourteenth embodiment, it is also advantageous to use the high-frequency acceleration unit 6. In principle, the same operating method as used in the fourteenth embodiment can be used in the fifteenth embodiment.
In the broad beam method, the beam must be emitted with an exposure dose error approximately equal to that in the spot-scanning irradiation. However, the duration of each irradiation cycle can be defined in terms of percentage in the total irradiation time in the broad beam method, unlike the case of the spot-scanning irradiation. Therefore, there arises no problem if the synchrotron 200 can terminate beam extraction within about 1 ms upon receiving the command signal. The synchrotron 200 can terminate beam extraction by simply turning on and off the extraction quadrupole electromagnet unit 9 within this time period if ON time of the extraction quadrupole electromagnet unit 9 per extraction cycle is about 1 ms. If the ON time of the extraction quadrupole electromagnet unit 9 per extraction cycle is longer than this, the beam path bending electromagnet unit 16 or the beam blocking electromagnet unit 18 in the beam transport line 300 may be used instead of the extraction quadrupole electromagnet unit 9 for terminating beam extraction. As it is possible to terminate beam extraction without any problem by varying the magnetic field in about 1 ms, the fifteenth embodiment serves to provide a low-cost particle beam radiation therapy system. If the ON time of the extraction quadrupole electromagnet unit 9 per extraction cycle is too long, the stable region of resonance reduces too much and the direction of the extracted beam varies by a large amount. Thus, if it is necessary to increase the ON time of the extraction quadrupole electromagnet unit 9, the ON time should be set to a value within a permissible range.
It will be appreciated from the foregoing discussion that the invention produces the same advantageous effects as in the spot-scanning irradiation method when applied to the broad beam method according to the fifteenth embodiment. Specifically, the fifteenth embodiment is advantageous in that the synchrotron 200 can extract the particle beam during desired periods of time only and provide a low-cost particle beam radiation therapy system.
The first to fifteenth embodiments thus far described are applicable to particle beam radiation therapy systems for treating cancers and other malignant tumors, as well as sterilization, disinfection, improvement of properties of metallic materials and physical experiments by use of a charged-particle beam.
While the invention has been described in conjunction with the specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, the invention is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims.
Number | Date | Country | Kind |
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2004-122481 | Apr 2004 | JP | national |
2004-180532 | Jun 2004 | JP | national |