CN107580404B - Control method for linear accelerator and linear accelerator - Google Patents
Control method for linear accelerator and linear accelerator Download PDFInfo
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Abstract
The invention provides a control method for a linear accelerator and the linear accelerator applying the method, the control method is used for stabilizing the dosage rate of emergent rays of the linear accelerator, the linear accelerator comprises a microwave power source used for generating accelerating microwave pulses, an accelerating tube used for accelerating injected electron pulses and an automatic frequency stabilizing module used for tuning the frequency of the accelerating microwave pulses, wherein during the switching period of a first state with ray beams and a second state without ray beams, the automatic frequency stabilizing module locks the frequency of the accelerating microwave pulses to the working frequency of the accelerating tube in the first state or the second state. The method and the linear accelerator can enable the emergent ray beam to have stable dosage rate.
Description
Technical Field
The invention mainly relates to the field of linear accelerators, in particular to a method for stabilizing the dose rate of emergent ray beams and a linear accelerator.
Background
As shown in fig. 1, the Cone Beam CT (CBCT) has a basic principle that a Cone beam X-ray source 10 and a detector 2 are relatively fixed, and are scanned in a direction a around an object 3 to obtain two-dimensional projection images of the object 3 at various angles, and then a three-dimensional image of the inside of the object 3 is constructed by using a reconstruction algorithm. At present, CBCT has been widely used for imaging of oral cavity, skull, etc., and is also used for setup confirmation in Image Guided Radiation Therapy (IGRT).
In general, a CBCT consists of one 360-circle image or one-half 180-circle images, where a single image corresponds to a short time out-of-beam (e.g., 60 ms) and the gantry is moved only without out-of-beam (i.e., with the beam stopped, e.g., 140 ms) between the two images. In the above-mentioned rotational scanning process, the working flow of CBCT is the repetition of beam-out-stop-beam-out-stop from the viewpoint of imaging beam current.
Fig. 2 shows a conventional X-ray source 10, which includes an electron injector 11, an acceleration tube 12, an imaging target 13, an Automatic Frequency Control (AFC) module 14, a magnetron 15, and a circulator 16. Referring to fig. 2 and 3, the electron injector 11 generates an injected electron Pulse (INJ Pulse) and injects it into the accelerating tube 12, and the magnetron 15 generates an accelerated microwave Pulse (RF Pulse) and outputs it to the accelerating tube 12 through the circulator 16. When the injected electron Pulse and the accelerating microwave Pulse coincide (synchronize), the injected electrons can be accelerated, and the imaging target 13 is bombarded by the accelerated electron Pulse (E Pulse) to output an imaging beam current (X-ray Pulse), that is, the X-ray source 10 outputs a beam current. When the injected electron pulse and the accelerating microwave pulse do not coincide, the injected electrons cannot be accelerated, and no imaging beam current is generated, i.e., the X-ray source 10 stops. Thus, the X-ray source 10 typically employs varying time delays for the injection of the electron pulses and the acceleration of the microwave pulses to switch between synchronous and asynchronous, thereby switching between beaming and beaming shutdowns.
Considering that the state of the accelerating tube 12 varies with the temperature of the system, etc., the AFC module 14 is required to match the frequency of the accelerating microwave pulse input to the accelerating tube 12 and the operating frequency of the accelerating tube 12. If the frequency of the accelerating microwave pulse is mismatched with the operating frequency of the accelerating tube 12, the dosage rate of the imaging beam current is reduced. Generally, after the system is turned on, the AFC module 14 continuously tunes the frequency of the accelerated microwave pulse signal according to the incident wave (FWD) and the reflected wave (REF) returned through the circulator 16, so that the frequency of the accelerated microwave pulse is kept matched to the operating frequency of the acceleration tube 12, and thus the dose rate of the imaging beam is kept stable. However, under the condition that the AFC module 14 continuously works, the situation that the dose rate of the imaging beam is unstable still occurs, and the imaging quality is affected, which is a technical problem that medical imaging equipment such as CBCT, especially MV-level CBCT, needs to solve urgently.
Disclosure of Invention
The invention aims to provide a method for stabilizing a ray beam and a linear accelerator applying the method, which can enable the emergent ray beam to have stable dosage rate.
In order to solve the technical problem, the present invention provides a control method for a linear accelerator, where the linear accelerator includes a microwave power source for generating an accelerating microwave pulse, an acceleration tube for accelerating an injected electron pulse, an automatic frequency stabilization module for tuning a frequency of the accelerating microwave pulse, and a target for converting the accelerated electron pulse into a beam, and the control method is characterized in that during a switching period between a first state with the beam and a second state without the beam, the automatic frequency stabilization module locks the frequency of the accelerating microwave pulse to a working frequency of the acceleration tube in the first state or the second state.
In an embodiment of the invention, the second state comprises a state in which the injected electron pulse is asynchronous to the accelerated microwave pulse, or a state in which the injected electron pulse is switched off while the accelerated microwave pulse is switched on.
In an embodiment of the present invention, in the first state, the automatic frequency stabilization module is configured to enable the accelerating microwave pulse frequency to follow the operating frequency of the accelerating tube; in the second state, the auto-frequency stabilization module is configured to not tune the accelerated microwave pulse frequency.
In an embodiment of the present invention, in the first state, the automatic frequency stabilization module is configured to be turned on; in the second state, the auto-frequency stabilization module is configured to turn off.
In an embodiment of the invention, the automatic frequency stabilization module is configured to be turned off during a warm-up phase of the acceleration tube.
In an embodiment of the present invention, in the second state, the automatic frequency stabilization module is configured to enable the accelerating microwave pulse frequency to follow the operating frequency of the accelerating tube under the current condition; in the first state, the auto-frequency stabilization module is configured to not tune the accelerated microwave pulse frequency.
In an embodiment of the present invention, in the second state, the automatic frequency stabilization module is configured to be turned on; in the first state, the auto-frequency stabilization module is configured to turn off.
In an embodiment of the present invention, during the preheating phase of the acceleration tube, the automatic frequency stabilization module is configured to be turned on.
In an embodiment of the present invention, during the switching between the first state and the second state, the automatic frequency stabilization module is turned on; wherein the auto-frequency stabilization module is configured to a first phase in one of the first or second states and a second phase different from the first phase in the other of the first or second states.
In an embodiment of the present invention, during the switching between the first state and the second state, the automatic frequency stabilization module is turned on; wherein the auto-frequency stabilization module is configured with a bias phase that is enabled in one of the first or second states and disabled in the other of the first or second states.
In an embodiment of the invention, during the preheating phase of the acceleration tube, the automatic frequency stabilization module is configured to be turned on, and the bias phase is enabled or disabled.
Another aspect of the present invention further provides a method for improving beam current stability of a linear accelerator, wherein the linear accelerator comprises a microwave power source for generating an accelerating microwave pulse, an acceleration tube for accelerating an injected electron pulse, an automatic frequency stabilization module for tuning a frequency of the accelerating microwave pulse, and a target for converting the accelerated electron pulse into a beam current, wherein the automatic frequency stabilization module is configured to be turned on only in one of a first state and a second state during switching of the first state in which the injected electron pulse is synchronized with the accelerating microwave pulse and the second state in which the injected electron pulse is asynchronous with the accelerating microwave pulse.
In another aspect of the present invention, there is provided a method for improving beam current stability of a linear accelerator, wherein the linear accelerator comprises a microwave power source for generating an accelerating microwave pulse, an acceleration tube for accelerating an injected electron pulse, an automatic frequency stabilization module for tuning a frequency of the accelerating microwave pulse, and a target for converting the accelerated electron pulse into a beam current, wherein the automatic frequency stabilization module is configured such that the frequency of the accelerating microwave pulse is substantially the same in a first state and a second state during switching of the first state in which the injected electron pulse is synchronized with the accelerating microwave pulse and the second state in which the injected electron pulse is asynchronous with the accelerating microwave pulse.
Another aspect of the present invention also provides a linear accelerator, including: a microwave power source for generating an accelerating microwave pulse; an acceleration tube for accelerating the injected electron pulses; the automatic frequency stabilization module is used for tuning the acceleration microwave pulse frequency; the target is used for converting the accelerated electronic pulse into a ray beam; the automatic frequency stabilization module locks the frequency of the acceleration microwave pulses to the working frequency of the acceleration tube in the first state or the second state during the switching period of the first state with the ray beam and the second state without the ray beam.
In an embodiment of the invention, the second state comprises a state in which the injected electron pulse is asynchronous to the accelerated microwave pulse, or a state in which the injected electron pulse is switched off while the accelerated microwave pulse is switched on.
In an embodiment of the present invention, in the first state, the automatic frequency stabilization module makes the frequency of the accelerated microwave pulse follow the operating frequency of the acceleration tube; in the second state, the automatic frequency stabilization module does not tune the accelerating microwave pulse frequency.
In an embodiment of the present invention, in the first state, the automatic frequency stabilization module is configured to be turned on; in the second state, the auto-frequency stabilization module is configured to turn off.
In an embodiment of the invention, the automatic frequency stabilization module is configured to be turned off during a warm-up phase of the acceleration tube.
In an embodiment of the present invention, in the second state, the automatic frequency stabilization module makes the acceleration microwave pulse frequency follow the operating frequency of the acceleration tube under the current condition; in the first state, the automatic frequency stabilization module does not tune the accelerating microwave pulse frequency.
In an embodiment of the present invention, in the second state, the automatic frequency stabilization module is configured to be turned on; in the first state, the auto-frequency stabilization module is configured to turn off.
In an embodiment of the present invention, during the preheating phase of the acceleration tube, the automatic frequency stabilization module is configured to be turned on.
In an embodiment of the present invention, during the switching between the first state and the second state, the automatic frequency stabilization module is turned on; wherein the auto-frequency stabilization module is configured to a first phase in one of the first or second states and a second phase different from the first phase in the other of the first or second states.
In an embodiment of the present invention, during the switching between the first state and the second state, the automatic frequency stabilization module is turned on; wherein the automatic frequency stabilization module is configured with an offset phase; the bias phase is enabled in one of the first or second states and is disabled in the other of the first or second states.
In an embodiment of the present invention, during the preheating phase of the acceleration tube, the automatic frequency stabilization module is turned on, and the bias phase is enabled or disabled.
Another aspect of the present invention provides another linear accelerator, including: a microwave power source for generating an accelerating microwave pulse; an acceleration tube for accelerating the injected electron pulses; the automatic frequency stabilization module is used for tuning the acceleration microwave pulse frequency; the target is used for converting the accelerated electronic pulse into a ray beam; wherein during a first state in which the injected electron pulses are synchronized with the accelerating microwave pulses and a second state in which the injected electron pulses are asynchronous with the accelerating microwave pulses, the auto-stabilization module is configured to be on only in one of the first state and the second state.
Another aspect of the present invention provides another linear accelerator, including: a microwave power source for generating an accelerating microwave pulse; an acceleration tube for accelerating the injected electron pulses; the automatic frequency stabilization module is used for tuning the acceleration microwave pulse frequency; the target is used for converting the accelerated electronic pulse into a ray beam; wherein during a first state in which the injected electron pulses are synchronized with the accelerating microwave pulses and a second state in which the injected electron pulses are asynchronous with the accelerating microwave pulses, the auto-stabilization module is configured such that the accelerating microwave pulse frequency is substantially the same in the first state and the second state.
Another aspect of the present invention also provides a cone-beam CT comprising an electron accelerator as described above.
Compared with the prior art, the invention has the following advantages: compared with the prior art that the AFC module continuously works and enables the frequency of the accelerating microwave pulse to continuously change along with the working frequency of the accelerating tube, in the method for stabilizing the ray beam, the frequency of the accelerating microwave pulse is locked to the working frequency of the accelerating tube in the first state or the second state during the switching period of the first state with the ray beam and the second state without the ray beam, the condition that the energy of the electron pulse accelerated by the accelerating tube fluctuates due to the fact that the difference between the frequency of the accelerating microwave pulse and the working frequency of the accelerating tube changes during the tuning period of the frequency of the accelerating microwave pulse does not exist, the energy of the accelerating electron pulse is stabilized, and therefore the dose stability of the ray beam is improved.
Drawings
Fig. 1 is a basic principle schematic diagram of cone-beam CT.
Fig. 2 is a basic block diagram of a conventional X-ray source.
Fig. 3 is a schematic view of the workflow of a prior art X-ray source.
Fig. 4 is a basic block diagram of a linear accelerator according to an embodiment of the present invention.
Fig. 5 is a basic flowchart of a method for stabilizing a beam current according to an embodiment of the present invention.
Fig. 6 is a schematic diagram of the workflow of a linear accelerator according to an embodiment of the present invention.
Fig. 7 is a schematic diagram of the workflow of a linear accelerator according to another embodiment of the present invention.
Fig. 8 is a schematic diagram of the workflow of a linear accelerator according to another embodiment of the present invention.
Fig. 9 is a basic block diagram of cone-beam CT according to an embodiment of the present invention.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described herein, and thus the present invention is not limited to the specific embodiments disclosed below.
As used in this application and the appended claims, the terms "a," "an," "the," and/or "the" are not intended to be inclusive in the singular, but rather are intended to be inclusive in the plural unless the context clearly dictates otherwise. In general, the terms "comprises" and "comprising" merely indicate that steps and elements are included which are explicitly identified, that the steps and elements do not form an exclusive list, and that a method or apparatus may include other steps or elements.
As described in the background, the conventional X-ray source 10 still has an unstable dose rate of the imaging beam current when the AFC module 14 is in continuous operation. The inventors of the present invention found that one of the main causes of instability of the dose rate of the imaging beam is: in order to achieve the repeated switching of the X-ray source 10 between the outgoing beam and the stopped beam, the acceleration tube 12 is repeatedly switched between a first state with a beam current, which is typically an X-ray beam current, and a second state without the beam current. In the case where the AFC module 14 is continuously operating, the frequency of the accelerated microwave pulses will follow the operating frequency of the accelerating tube, while the operating frequency of the accelerating tube 12 will have a difference between the first state and the second state, which results in the accelerated microwave pulse frequency needing to be repeatedly switched between the operating frequencies of the accelerating tube in the first state and the second state. However, when the AFC module 14 tunes the frequency of the accelerating microwave pulse from the operating frequency of the accelerating tube 12 in the first state to the operating frequency of the accelerating tube 12 in the second state, or tunes the frequency of the accelerating tube 12 in the second state to the operating frequency of the accelerating tube 12 in the first state, a certain time is required to not timely follow the operating frequency of the accelerating tube 12, and the difference between the frequency of the accelerating microwave pulse and the operating frequency of the accelerating tube 12 varies with the tuning, which causes the energy of the electron pulse accelerated by the accelerating tube 12 to fluctuate, and further causes the dose rate of the imaging beam current to fluctuate. Particularly when the period of time is greater than or equal to the duration of the beam-out or beam-off, the AFC module 14 constantly tunes the frequency of the accelerating microwave pulses, at which time the dose rate of the imaging beam current continuously fluctuates. In the context of the present invention, the first state of the beam current generally comprises: an accelerating microwave pulse from a power source such as a magnetron is fed into the acceleration tube, an electron pulse from an electron pulse generating source such as an electron gun is injected into the acceleration tube, and the electron pulse is synchronized with the accelerating microwave pulse. The second state of the beam current generally includes: an accelerating microwave pulse from a power source (such as a magnetron) is fed into the acceleration tube, an electron pulse from an electron pulse generating source (such as an electron gun) is injected into the acceleration tube, and the electron pulse is asynchronous to the accelerating microwave pulse; alternatively, an accelerating microwave pulse from a power source (such as a magnetron) is fed into the acceleration tube, but an electron pulse from a source such as an electron pulse generating source (such as an electron gun) is turned off. It should be understood that the first state with the beam current is defined as long as the accelerating tube has the emergent beam current available for imaging or treatment, and the second state without the beam current is defined as long as the accelerating tube does not have the emergent beam current available for imaging or treatment. The above description of the first state with the beam current and the second state without the beam current is only for facilitating the understanding of the technical solution of the present invention by the skilled person, especially for the understanding of the technical solution of the present invention mentioned to apply CBCT, and they are not restrictive.
The inventors of the present invention have proposed, based on the above findings, that during switching between a first state with a beam current and a second state without a beam current, the AFC module locks the frequency of the accelerating microwave pulses to the operating frequency of the acceleration tube in the first state or the second state. Therefore, the frequency of the accelerating microwave pulse is not repeatedly switched between the working frequencies of the accelerating tube in the first state and the second state, so that the fluctuation of the energy of the electron pulse caused by the analyzed reasons does not exist, the energy of the electron pulse is stabilized, and the dosage rate of the emergent ray beam is stabilized.
Fig. 4 is a basic block diagram of a linear accelerator according to an embodiment of the present invention. Referring to fig. 4, the linac 20 mainly includes a microwave power source 22 for generating an accelerating microwave Pulse (RF Pulse), an accelerating tube 21 for accelerating an injected electron Pulse (INJ Pulse) according to the accelerating microwave Pulse, an automatic frequency stabilization (AFC) module 23 for tuning the frequency of the accelerating microwave Pulse, and a target 24 for converting the accelerated electron Pulse into a beam current (X-ray Pulse). The linac 20 may further include a circulator 25, the circulator 25 being configured to split a portion of the accelerated microwave pulses output from the microwave power source 22 to form an incident wave (FWD), and to output the incident wave and a reflected wave (REF) reflected back from the acceleration tube 21 to the AFC module 23. The AFC module 23 may tune the accelerated microwave pulse frequency based on the received incident and reflected waves.
Fig. 5 is a basic flowchart of a method for stabilizing a beam current according to an embodiment of the present invention. Referring to fig. 5, a method 30 for stabilizing a beam current is applied to the energy of the accelerated electron pulses of the linac 20 shown in fig. 4, and mainly includes steps 31: during the repeated switching of the first state with the beam current and the second state without the beam current, the AFC module 23 locks the frequency of the accelerating microwave pulse to the operating frequency of the accelerating tube 21 in the first state or the second state.
In one embodiment, during a first state of beam current, the AFC module 23 is enabled to cause the accelerating microwave pulse frequency to follow the operating frequency of the accelerating tube 21 when in the first state; during a second state of the nonradiative beam current, the AFC module is disabled so as not to affect the accelerating microwave pulse frequency. In this way, the frequency of the accelerating microwave pulses can be locked to the operating frequency of the acceleration tube 21 in the first state during repeated switching between the first state with the beam current and the second state without the beam current.
Fig. 6 is a schematic diagram of the workflow of a linear accelerator according to an embodiment of the present invention. Referring to fig. 4 to 6, the working flow mainly includes a preheating phase and a working phase formed by alternating a plurality of first state periods with the beam current and second state periods without the beam current.
In the preheating stage, the accelerating microwave pulses are fed into the accelerating tube 21, the injected electron pulses are asynchronous to the accelerating microwave pulses, and the electron accelerator 20 is brought to a steady state by setting a reasonably selected preset AFC position. During this time, the AFC module 23 is in the off state, and the accelerating microwave pulse frequency does not follow the operating frequency of the accelerating tube 21.
In the working phase, the first frame period is divided into a beam period with rays and a beam period without rays, wherein in the beam period with rays, an electron pulse is injected to be synchronous with an acceleration microwave pulse, and the AFC module 23 is started to enable the frequency of the acceleration microwave pulse to follow the working frequency of the acceleration tube 21 in the first state; during the period of no-ray beam, the injection pulse and the acceleration microwave pulse are asynchronous, the AFC module 23 is closed, and the frequency of the acceleration microwave pulse is kept at the frequency during closing and does not change along with the working frequency of the acceleration tube 21. A second frame period, which is similarly divided into a beam period with rays and a beam period without rays, wherein in the beam period with rays, the injected electron pulse and the accelerated microwave pulse are synchronized again, and the AFC module 23 is started again, so that the frequency of the accelerated microwave pulse follows the working frequency of the accelerating tube 21 in the first state again; during the period of no beam current, the injected electron pulses are again asynchronous to the accelerating microwave pulses, turning off the AFC module 23. And repeating the steps until the working phase is finished. In summary, the above process is to turn on the AFC module 23 during the synchronization of the injected electron pulse and the accelerated microwave pulse; during the period when the injected electron pulse is asynchronous to the accelerated microwave pulse, the AFC module 23 is turned off. In this process, during the period of the non-beam, the AFC module 23 is in the disabled state, and it does not tune the frequency of the accelerated microwave pulse, so that the frequency of the accelerated microwave pulse also shifts, but since this period is usually short, for example, 140ms in CBCT, when the AFC module 23 is turned on again, the frequency shift of the accelerated microwave pulse is small (compared to the difference between the operating frequencies of the acceleration tube 21 in the first state and the second state), the AFC module 23 can quickly lock the frequency of the accelerated microwave pulse to the operating frequency of the acceleration tube 21 in the first state again, and can well stabilize the energy of the electron pulse accelerated by the acceleration tube 21, so that the stability of the beam pulse is high, the dose of each obtained frame image is almost equal, and finally the imaging quality of the CBCT is improved.
In one embodiment, during the period when the injection of the electron pulse is asynchronous to the acceleration microwave pulse, the AFC module 23 is enabled or turned on so that the frequency of the acceleration microwave pulse follows the operating frequency of the acceleration tube 21 in the second state of the beam current; during the time that the injected electronic pulses are synchronized with the accelerating microwave pulses, the AFC module is disabled or turned off, and thus the accelerating microwave pulse frequency is not tuned. In this way, the frequency of the accelerating microwave pulses can be locked to the operating frequency of the acceleration tube 21 in the second state during repeated switching between the first state with the beam current and the second state without the beam current.
Fig. 7 is a schematic diagram of the workflow of a linear accelerator according to another embodiment of the present invention. Referring to fig. 4, 5 and 7 in combination, the work flow also includes a preheating phase and a working phase.
In the preheating stage, the acceleration microwave pulse is fed into the acceleration tube 21, the injected electron pulse is asynchronous with the acceleration microwave pulse, the AFC module 23 is turned on, and the frequency of the acceleration microwave pulse follows the working frequency of the acceleration tube 21, that is, is locked to the working frequency of the acceleration tube 21 in the second state of no beam current.
In the working phase, the first frame is divided into a beam current period with rays and a beam current period without rays, wherein in the beam current period with rays, the injected electron pulse is synchronous with the acceleration microwave pulse, the AFC module 23 is closed, and the frequency of the acceleration microwave pulse is kept at the frequency when the AFC module is closed and does not change along with the working frequency of the acceleration tube 21; during the period of no-ray beam, the injected electron pulse is asynchronous with the acceleration microwave pulse, and the AFC module 23 is turned on again, so that the frequency of the acceleration microwave pulse follows the working frequency of the acceleration tube 21 in the second state. Similarly, the second frame can be divided into a beam current period with rays and a beam current period without rays, and in the beam current period with rays, the injection of electron pulses and the acceleration of microwave pulses are synchronized again, and the AFC module 23 is closed; during the period of no-ray beam, the injected electron pulse and the accelerated microwave pulse are asynchronous again, and the AFC module 23 is started again, so that the frequency of the accelerated microwave pulse follows the working frequency of the accelerating tube 21 in the second state. And repeating the steps until the working phase is finished. In summary, the above process is to turn on the AFC module 23 during the asynchronous period between the injection of the electron pulse and the acceleration of the microwave pulse; the AFC module 23 is switched off during the injection of the electron pulses in synchronism with the accelerating microwave pulses. In this process, the AFC module 23 does not tune the acceleration microwave pulse frequency during the period when the injected electron pulse and the acceleration microwave pulse are synchronized, and the acceleration microwave pulse frequency also shifts, but since this period is usually short, for example, 60ms in CBCT, when the AFC module 23 is turned on again, the shift of the acceleration microwave pulse frequency is small (compared to the difference between the operating frequencies of the acceleration tube 21 in the first state and the second state), the AFC module 23 can quickly lock the acceleration microwave pulse frequency again to the operating frequency of the acceleration tube 21 in the second state, and can well stabilize the energy of the electron pulse accelerated by the acceleration tube 21, thereby improving the dose stability of the emitted beam current.
Compared with the embodiment shown in fig. 6, the embodiment shown in fig. 7 has the AFC module 23 turned on during the warm-up phase, and can automatically bring the linac 20 to a steady state, so that a reasonably selected preset AFC position does not need to be set. In addition, since the embodiment shown in fig. 7 locks the frequency of the acceleration microwave pulse to the operating frequency of the acceleration tube 21 in the second state without the beam current, and this frequency is not the optimal operating frequency of the acceleration tube 21, the energy of the acceleration electron pulse is small, and the dose rate of the emitted beam current is small, but the output dose of the acceleration tube 21 can be stabilized well.
In an alternative embodiment, the AFC module 23 may be turned on in only one of the first state and the second state. In the on state, the AFC module 23 may be the same as the AFC module 23 in the previous embodiment, and thus will not be described in detail herein.
In addition, it should be noted that, the AFC module 23 may be turned on or turned off according to an external control signal, or according to a control signal generated by the AFC module 23 itself, which is not limited in the present invention.
In one embodiment, the AFC block 23 is turned on during repeated switching of the first state with the beam current and the second state without the beam current, and the AFC block 23 is configured to the first phase during one of the first state with the beam current and the second state without the beam current, and the AFC block 23 is configured to the second phase different from the first phase during the other one of the first state with the beam current and the second state without the beam current. The frequency of the accelerated microwave pulses is tuned by the AFC block 23 in the first and second phases, and the operating frequency of the accelerated microwave pulses is substantially the same or similar in both states.
In one embodiment, during the second state of the non-beam current, the AFC module 23 is configured with a bias phase, under which the AFC module 23 tunes the accelerating microwave pulse frequency to be approximately or the same as the operating frequency of the accelerating tube 21 in the first state, so that the accelerating microwave pulse frequency is continuously locked to or near the operating frequency of the accelerating tube 21 in the first state during repeated switching between the first state of the beam current and the second state of the non-beam current. In another embodiment, the AFC module 23 may be configured with a bias phase during the first state with the beam current, under which the AFC module 23 tunes the accelerating microwave pulse frequency to be similar or identical to the operating frequency of the accelerating tube 21 in the second state, so that the accelerating microwave pulse frequency is continuously locked to or near the operating frequency of the accelerating tube 21 in the second state during repeated switching between the first state with the beam current and the second state without the beam current.
While the following description is made by taking as an example the case where the AFC block 23 is configured with the offset phase during the second state without the beam current, it will be understood by those skilled in the art that the following description is equally applicable to the case where the AFC block 23 is configured with the offset phase during the first state with the beam current, the first phase and the second phase are configured in the first state and the second state, respectively, and so on.
Fig. 8 is a schematic diagram of the workflow of an electron accelerator according to another embodiment of the present invention. Referring to fig. 4, 5 and 8 in combination, the work flow also includes a preheating phase and a working phase.
During the warm-up phase, accelerated microwave pulses are fed into the acceleration tube 21, the injected electron pulses are asynchronous to the accelerated microwave pulses, the AFC module 23 is turned on, and a bias phase is configured for the AFC module 23. At this time, the AFC module 23 tunes the frequency of the accelerating microwave pulse to be similar to or the same as the operating frequency of the accelerating tube 21 in the first state with the beam current under the action of the offset phase.
In the working phase, the first frame is divided into a first state period with a ray beam and a second state period without the ray beam, and in the period with the ray beam, the phase offset of the AFC module 23 is cancelled, and at this time, the AFC module 23 makes the frequency of the accelerating microwave pulse follow the working frequency of the accelerating tube 21 in the first state; during the second state of the non-beam current, the injected electron pulse is asynchronous to the accelerated microwave pulse, the AFC module 23 is again configured with a bias phase, and the AFC module 23, under the action of the bias phase, tunes the frequency of the accelerated microwave pulse to be similar to or the same as the operating frequency of the acceleration tube 21 in the first state. Similarly, the second frame may be divided into a first state period with a beam and a second state period without a beam, and during the first state period with a beam, the injection pulse is synchronized with the acceleration microwave pulse to cancel the phase offset of the AFC module 23; during the second state of the non-beam current, the injection pulse is asynchronous with the accelerating microwave pulse, again configuring the AFC module 23 with a bias phase. And repeating the steps until the working phase is finished. In this process, the frequency of the accelerated microwave pulses is continuously locked to the operating frequency of the acceleration tube 21 in the first state or in the vicinity of the operating frequency, the frequency of the accelerated microwave pulses changes little (compared to the difference between the operating frequencies of the acceleration tube 21 in the first state and the second state), and the AFC module 23 can quickly lock the frequency of the accelerated microwave pulses again to the operating frequency of the acceleration tube 21 in the first state, so that the dose rate of the emitted beam can be stabilized well.
The embodiment shown in fig. 8 starts the AFC module 23 during the warm-up phase, and configures the AFC module 23 with a bias phase, and the AFC module 23 can automatically stabilize the electron accelerator 20 under the bias phase, so that there is no need to set a properly selected preset AFC position.
It should also be noted that the configuration of the bias phase for the AFC module 23 may be performed by an external control signal, or may be performed by a control signal inside the AFC module 23.
It should be appreciated that while the embodiment shown in fig. 8 illustrates configuring the AFC with a bias phase during the second state without beam current, this is not a limitation, and one skilled in the art would recognize that the AFC may be configured with a bias phase during the first state with beam current. Likewise, it is also understood that a first bias phase may be configured for the AFC during a first state with beam current, while a second bias phase different from the first bias phase is configured for the AFC during a second state without beam current.
It should be appreciated that although the second state of the beam current is achieved by injecting the electron pulse asynchronously (or asynchronously) with the accelerating microwave pulse in the foregoing description of fig. 6, 7 and 8, it is also possible to temporarily turn off the injected electron pulse. It is also to be understood that the present invention does not exclude other technical means to achieve the second state of the beam current.
It will be appreciated that the target 24 in the linac 20 may be an imaging target that, upon bombardment with pulses of accelerated electrons, outputs an imaging beam for imaging. The target 24 in the linac 20 may also be a treatment target that, after being bombarded by the accelerated electron pulses, outputs radiation for treatment. The present invention is not limited to the specific form of the target 24.
Fig. 9 is a basic block diagram of cone-beam CT according to an embodiment of the present invention. Referring to fig. 9, a cone-beam CT 40 includes the linear accelerator 20 and the detector 2 as shown in fig. 4. Since the imaging beam output by the linac 20 has a stable dose, a multi-frame cone beam CT image with a stable dose passing through the object 3 (typically, a human body) can be obtained, and thus the imaging quality of the cone beam CT 40 can be optimized.
Although the present invention has been described with reference to the present specific embodiments, it will be appreciated by those skilled in the art that the above embodiments are merely illustrative of the present invention, and various equivalent changes and substitutions may be made without departing from the spirit of the invention, and therefore, it is intended that all changes and modifications to the above embodiments within the spirit and scope of the present invention be covered by the appended claims.
Claims (25)
1. A control method for a linear accelerator comprising a microwave power source for generating accelerating microwave pulses, an acceleration tube for accelerating injected electron pulses, an automatic frequency stabilization module for tuning the frequency of the accelerating microwave pulses and a target for converting the accelerated electron pulses into a beam current, characterized in that during switching between a first state with beam current and a second state without beam current, the automatic frequency stabilization module locks the frequency of the accelerating microwave pulses to the operating frequency of the acceleration tube in one of the first or second state.
2. The control method according to claim 1, wherein the second state comprises a state in which the injected electron pulse is asynchronous to the accelerated microwave pulse, or a state in which the injected electron pulse is turned off while the accelerated microwave pulse is turned on.
3. The method of claim 1, wherein in the first state, the automatic frequency stabilization module is configured to enable the accelerating microwave pulse frequency to follow an operating frequency of the accelerating tube; in the second state, the auto-frequency stabilization module is configured to not tune the accelerated microwave pulse frequency.
4. The method of claim 3, wherein in the first state, the automatic frequency stabilization module is configured to be on; in the second state, the auto-frequency stabilization module is configured to turn off.
5. The method of claim 3, wherein the auto-stabilization module is configured to shut down during a warm-up phase of the acceleration tube.
6. The method of claim 1, wherein in the second state, the automatic frequency stabilization module is configured to enable the accelerating microwave pulse frequency to follow an operating frequency of the accelerating tube under current conditions; in the first state, the auto-frequency stabilization module is configured to not tune the accelerated microwave pulse frequency.
7. The method of claim 6, wherein in the second state, the automatic frequency stabilization module is configured to be on; in the first state, the auto-frequency stabilization module is configured to turn off.
8. The method of claim 6, wherein the auto-frequency stabilization module is configured to turn on during a warm-up phase of the acceleration tube.
9. The method of claim 1, wherein the automatic frequency stabilization module is turned on during the switching of the first state and the second state; wherein the auto-frequency stabilization module is configured to a first phase in one of the first or second states and a second phase different from the first phase in the other of the first or second states.
10. The method of claim 1, wherein the automatic frequency stabilization module is turned on during the switching of the first state and the second state; wherein the auto-frequency stabilization module is configured with a bias phase that is enabled in one of the first or second states and disabled in the other of the first or second states.
11. A method of improving beam stability of a linear accelerator, wherein the linear accelerator comprises a microwave power source for generating accelerating microwave pulses, an acceleration tube for accelerating injected electron pulses, an auto-frequency stabilization module for tuning the frequency of the accelerating microwave pulses, and a target for converting the accelerated electron pulses into a beam, characterized in that the auto-frequency stabilization module is configured to be on only in one of the first state and the second state during switching of a first state in which the injected electron pulses are synchronized with the accelerating microwave pulses and a second state in which the injected electron pulses are asynchronous with the accelerating microwave pulses.
12. A method of improving the beam stability of a linear accelerator, wherein the linear accelerator comprises a microwave power source for generating accelerating microwave pulses, an acceleration tube for accelerating injected electron pulses, an auto-frequency stabilization module for tuning the frequency of the accelerating microwave pulses, and a target for converting the accelerated electron pulses into a beam, characterized in that during switching between a first state in which the injected electron pulses are synchronized with the accelerating microwave pulses and a second state in which the injected electron pulses are asynchronous with the accelerating microwave pulses, the auto-frequency stabilization module is configured such that the accelerating microwave pulse frequency is the same in the first and second states.
13. A linear accelerator, comprising:
a microwave power source for generating an accelerating microwave pulse;
an acceleration tube for accelerating the injected electron pulses;
the automatic frequency stabilization module is used for tuning the acceleration microwave pulse frequency; and
the target is used for converting the accelerated electronic pulse into a ray beam;
the automatic frequency stabilization module locks the frequency of the accelerated microwave pulses to the working frequency of the accelerating tube in one of the first state and the second state during the switching period of the first state with the ray beam and the second state without the ray beam.
14. The linac of claim 13, wherein the second state comprises a state in which the injected electron pulse is asynchronous to the accelerating microwave pulse, or a state in which the injected electron pulse is turned off while the accelerating microwave pulse is turned on.
15. The linear accelerator of claim 13, wherein in the first state, the automatic frequency stabilization module causes the accelerating microwave pulse frequency to follow an operating frequency of the accelerating tube; in the second state, the automatic frequency stabilization module does not tune the accelerating microwave pulse frequency.
16. The linear accelerator of claim 14, wherein in the first state, the auto-frequency stabilization module is configured to turn on; in the second state, the auto-frequency stabilization module is configured to turn off.
17. The linear accelerator of claim 14, wherein the auto-stabilization module is configured to be off during a warm-up phase of the acceleration tube.
18. The linear accelerator of claim 13, wherein in the second state, the automatic frequency stabilization module causes the accelerating microwave pulse frequency to follow the operating frequency of the accelerating tube under current conditions; in the first state, the automatic frequency stabilization module does not tune the accelerating microwave pulse frequency.
19. The linear accelerator of claim 18, wherein in the second state, the auto-frequency stabilization module is configured to turn on; in the first state, the auto-frequency stabilization module is configured to turn off.
20. The linear accelerator of claim 18, wherein the auto-frequency stabilization module is configured to turn on during a warm-up phase of the acceleration tube.
21. The linear accelerator of claim 13, wherein the automatic frequency stabilization module is turned on during the switching of the first state and the second state; wherein the auto-frequency stabilization module is configured to a first phase in one of the first or second states and a second phase different from the first phase in the other of the first or second states.
22. The linear accelerator of claim 13, wherein the auto frequency stabilization module is turned on during the first and second state transitions; wherein the automatic frequency stabilization module is configured with an offset phase; the bias phase is enabled in one of the first or second states and is disabled in the other of the first or second states.
23. A linear accelerator, comprising:
a microwave power source for generating an accelerating microwave pulse;
an acceleration tube for accelerating the injected electron pulses;
the automatic frequency stabilization module is used for tuning the acceleration microwave pulse frequency; and
the target is used for converting the accelerated electronic pulse into a ray beam;
wherein during a first state in which the injected electron pulses are synchronized with the accelerating microwave pulses and a second state in which the injected electron pulses are asynchronous with the accelerating microwave pulses, the auto-stabilization module is configured to be on only in one of the first state and the second state.
24. A linear accelerator, comprising:
a microwave power source for generating an accelerating microwave pulse;
an acceleration tube for accelerating the injected electron pulses;
the automatic frequency stabilization module is used for tuning the acceleration microwave pulse frequency; and
the target is used for converting the accelerated electronic pulse into a ray beam;
wherein during a first state in which the injected electron pulses are synchronized with the accelerating microwave pulses and a second state in which the injected electron pulses are asynchronous with the accelerating microwave pulses, the auto-stabilization module is configured to cause the accelerating microwave pulse frequency to be the same in the first state and the second state.
25. A cone beam CT comprising a linac according to any one of claims 13 to 24.
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