Method and system for monitoring automatic frequency control between a radio frequency power source and a waveguide

Abstract

A method for monitoring automatic frequency control between an RF power source and a waveguide is disclosed herein. The method includes receiving a waveform of an RF pulse reflected from the waveguide. The method also includes plotting the waveform on a graph. The method also includes defining a tuning mask region on the waveform graph. The method also includes outputting an indication that a tuning requirement is met if the waveform covers the tuning mask region.

Description

Technical Field

[0001] The present disclosure relates to a system and method for quantifying the quality of automatic frequency control of a standing wave linear accelerator. Background Art

[0002] Radiation therapy uses ionizing radiation to damage or destroy unhealthy cells. Common forms of ionizing radiation include X-rays and charged particles.

[0003] A beam generation system is used to generate a radiation beam. The beam generation system is usually based on a particle accelerator (such as a linear accelerator or "linac"), which includes a radio frequency (RF) power source, a charged particle source, and an RF cavity. A linear accelerator (especially a medical linear accelerator) accelerates charged particles such as electrons to relativistic speeds along an acceleration path through an accelerating waveguide. The accelerating waveguide includes one or more resonant units surrounding the trajectory of the charged particles. The accelerating waveguide is filled with RF power from the RF power source, which forms an oscillating electric field or electromagnetic (EM) wave in the cavity. Charged particles are injected into the cavity from a particle source such as an electron gun, thereby forming a beam. When the beam passes through the oscillating EM wave, the beam gains energy and is thus accelerated, usually to relativistic speeds. The accelerated particles, whose effective mass is increased, deposit more energy when they collide with other matter, which is usually biological tissue or a tungsten target, which is used to generate X-rays. The particle beam or X-rays generated can be used for imaging or therapy, so the energy of the beam is often variable.

[0004] Many linear accelerators use standing waves to form the oscillating electric field required to accelerate charged particles in the waveguide. In these cases, the accelerating waveguide is configured for standing waves and is called a standing wave waveguide. The ideal standing wave is obtained by tuning the frequency of the RF power source to match the resonant frequency of the standing wave waveguide. The linear accelerator uses Automatic Frequency Control (AFC) to automatically tune the frequency between the RF power source and the standing wave waveguide. One type of AFC system is a phase-based feedback loop. If the quality of the AFC deteriorates, the frequency tuning will also deteriorate, energy from the RF power source will be wasted, and the quality of the treatment beam will be affected.

[0005] In known systems, indirect measurements can be used to monitor AFC quality, such as analyzing dose rate variations or using algorithms to characterize and monitor AFC. Dose rate variations can be affected by a variety of factors in the signal chain from the RF power source to the dosimetry system. Therefore, it is difficult to definitively attribute a dose rate change to a degradation in AFC quality. The algorithms used to characterize AFC performance can be based on information from the AFC itself, so the algorithm may fail when the AFC fails. In addition, if an incorrect frequency measurement is the cause of a degradation in AFC quality, it will be difficult for the algorithm to identify because the algorithm relies on the frequency measurement itself.

[0006] It is desirable to provide a system and method that solves the above problems. Summary of the invention

[0007] An invention is set out in the independent claim. Optional features are set out in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Embodiments will now be described by way of example with reference to the accompanying drawings, in which:

[0009] Figure 1 A beam generating system for a radiation therapy device is depicted;

[0010] Figure 2 A portion of a beam generating system for a radiation therapy device is depicted;

[0011] Figure 3 Draw the basis Figure 2 A portion of a beam generation system of the invention, and adding the system of the present disclosure;

[0012] Figure 4 The method of the present disclosure is depicted; and

[0013] Figure 5a and Figure 5b Two exemplary reflection waveforms are plotted, representing an RF pulse reflected from a waveguide and displayed on an oscilloscope screen. DETAILED DESCRIPTION

[0014] Overview

[0015] The wave reflected from the waveguide during filling is measured and compared to a predetermined area to give an estimate of the quality of the AFC.The reflected signal can be measured using a diode at the output of the circulator, which is unobtrusive and can be done temporarily as part of maintenance.

[0016] Specific description

[0017] Figure 1An exemplary beam generation system 200 is shown and will be generally described for the purpose of providing useful accompanying information to the present disclosure. The beam generation system 200 is based on a linear accelerator design.

[0018] The beam generation system 200 includes an accelerating waveguide 202 and an electron source 204. The electron source 204 may be an electron gun, such as a triode electron gun or a diode electron gun.

[0019] The accelerating waveguide 202 is configured to accelerate particles (in this case electrons) along an accelerating path 206 into a target 208 to produce a therapeutic radiation beam 210. The accelerating path 206 is also referred to as the central beam axis of the accelerating waveguide 202. The accelerating waveguide 202 includes a series of units. In this example, each unit has substantially the same shape and size, but in other examples, this may not be the case. The units may be arranged so that each unit is not coupled to RF or is independent of RF, and in this case, each unit acts as a separate resonant cavity. In other embodiments (e.g., Figure 1 In the example of ), the units can be coupled together, and in this case, the entire coupled structure can be considered as a single resonant cavity. In such an embodiment, although the coupled units act as a single resonant cavity, technicians in this field can still refer to the individual units as resonant cavities.

[0020] The acceleration path coincides with the central axis of the accelerating waveguide 202 and passes through a hole at the center of each cell. The accelerating waveguide 202, electron source 204, cells and target 208 are enclosed within an evacuated and vacuum-tight enclosure 212 to ensure that the propagation of the electrons is unimpeded as they travel toward the target 208.

[0021] The RF wave source or RF power source 214 (e.g., a magnetron or klystron, etc.) is configured to generate and / or amplify RF waves. The RF power source 214 is coupled to the accelerating waveguide 202 via RF transmission devices 216a, 216b, which generally include a copper waveguide portion that may have a circular or rectangular cross-section. The modulator is configured to input the RF wave into the accelerating waveguide 202 in a pulsed manner through the copper waveguide. Generally, the RF wave is input into a specific unit of the accelerating waveguide 202. The RF transmission devices 216a, 216b (which connect the RF power source 214 to the input unit of the accelerating waveguide 202) may include a waveguide network and may include an RF window that may separate the vacuum envelope from the SF6 envelope.

[0022] The RF transmission devices 216a, 216b are perpendicular to the central beam axis 206 of the accelerating waveguide 202, where they couple power into the input unit. The RF input of the connecting pipe or conduit is coupled to the accelerating waveguide 202 and engages the accelerating waveguide 202 at a substantially 90° angle. The RF transmission devices 216a, 216b may include a circulator 218 of any suitable known type. The RF transmission device may be defined as including two parts: a first part 216a, i.e., an RF transmission device coupling the RF power source 214 and the circulator 218; and a second part 216b, i.e., an RF transmission device coupling the circulator 218 and the waveguide 202.

[0023] Figure 1 The beam generation system of the invention operates in a standing wave configuration. The RF power source 214 is configured to input RF waves into the accelerating waveguide 202 in a pulsed manner to establish a standing wave of a varying electric field suitable for accelerating charged particles. Standing wave waveguide filling refers to the charging of the resonant waveguide cavity 202 to obtain the desired electromagnetic field required to accelerate charged particles. This is achieved by feeding RF power into the cavity. If the RF power source frequency is perfectly tuned to the waveguide resonant frequency, the RF power is converted into stored energy within the waveguide cavity during the filling phase. Otherwise, the waveguide will reflect most of the energy.

[0024] Figure 1 The circulator 218 shown in the figure can be a three-port device, with a first port coupled to the RF power source 214, a second port coupled to the waveguide 202, and a third port coupled to the reflected power load 222. The circulator is used to provide RF isolation between the pulsed RF source 214 and the waveguide 202. There can be a section of waveguide network 230 connecting the circulator to the reflected power load. At the first circulator port, the circulator 218 receives RF waves originating from the RF power source 214, which propagate from the RF source to the waveguide. The RF waves received at the first circulator port can be considered as forward propagating RF waves. The RF waves received at the first circulator port can only leave via the second circulator port, and these RF waves propagate to the waveguide and enter the waveguide. The RF waves travel in the waveguide and are transferred to the waveguide for storage as standing waves. The RF waves are reflected in the waveguide 202, leave the waveguide, and propagate toward the circulator 218, thereby traveling via the RF transmission device 216b. Reflected RF waves are received at the second circulator port, and these reflected waves can only leave via the third circulator port. The reflected waves propagate toward the reflected power load 222, also referred to as reflected energy dumping. The reflected waves are transferred to the reflected power load by the circulator 218, rather than propagating toward the RF power source 214 via the RF transmission device 216a. The reflected power load 222 absorbs the dissipated power from the reflected RF waves, typically with negligible reflection. The reflected power load 222 may be of any suitable type, such as a water load.

[0025] Alternatively, as will be appreciated by those skilled in the art, a four-port circulator may be employed. The four-port circulator may be used in a manner similar to the three-port circulator. For the four-port circulator, a first port may be coupled to the RF power source 214, a second port may be coupled to the waveguide 202, a third port may be coupled to a high-power reflected power load, and a fourth port may be coupled to a low-power reflected power load. The high-power reflected power load may be of any suitable type, such as a water load. The low-power reflected power load may be of any suitable type, such as a dry load or a load with a heat sink.

[0026] The RF power source 214 is typically operated in a pulsed mode. An exemplary RF wave frequency is 2998 MHz, with pulse durations in the microsecond range and pulse repetition rates in the hundreds of pulses per second range. The RF power source 214 can be a commercially available magnetron (e.g., an E2V 3.1 MW magnetron) or any standard radiotherapy magnetron covering an operating frequency of 2998 MHz.

[0027] In the accelerating waveguide formed by the coupled units, an RF standing wave is established according to the resonant frequency of the coupled structure. The effect of coupling the individual resonant units together to form a single resonant cavity is that, due to frequency dispersion, a band of oscillation modes of different frequencies, including high-order and low-order modes, can be allowed within the accelerating waveguide 202 on either side of the resonant frequency of the coupled structure. The frequency of the RF wave provided by the RF power source 214 defines the (one or more) modes excited in the waveguide 202. The resonant frequency and oscillation mode of the waveguide 202 will drift from their initial values ​​over time, so continuous tuning of the RF power source 214 is required to match the resonant frequency to establish an optimal standing wave. RF power source tuning is achieved via automatic frequency control (AFC).

[0028] There are also multiple modes of operation by which standing waves at the resonant frequency can accelerate electrons within the waveguide. Depending on the polarity of the electric field they experience, the electrons will be accelerated or decelerated. The length of each unit in the resonant cavity is designed so that the beam sees the same phase of the RF in each unit. The beam is synchronized so that at each oscillation the beam interacts with the positive portion of the wave and is further accelerated. In order for each mode of operation to work optimally, the frequency of the RF power source 214 needs to be tuned to the resonant frequency of the waveguide 202 via AFC.

[0029] An electron source 204 (eg, an electron gun) is also coupled to the accelerating waveguide 202 and is configured to inject electrons into the accelerating waveguide 202. The electron injection into the accelerating waveguide 202 is performed synchronously with the input of a radio frequency wave into the accelerating waveguide 202 in a pulsed manner.

[0030] Once the electrons are accelerated, they strike a heavy metal target 208. For example, the target 208 may include tungsten or another heavy metal. The impact of the electrons on the target 208 generates x-rays, which form a treatment beam 210.

[0031] refer to Figure 1 For a device, there may be or may be expected to be various variations in design and components, depending on the application requirements. For example, the requirements may vary depending on the required type and energy of the treatment beam or on the mechanical or structural design of the entire equipment (e.g., radiotherapy equipment) in which the device will be used.

[0032] Figure 2 Standard components involved in automatic frequency control (AFC) that form part of the beam generation system 200 are depicted.

[0033] The RF power source 214 is automatically frequency controlled 220 to ensure that the frequency of the RF power source is optimally tuned to the waveguide resonant frequency. The forward RF wave refers to the RF that is leaving the RF power source 214 and has not yet entered the waveguide 202. The reflected signal refers to the RF wave that has been reflected in the waveguide and has left the waveguide and is propagating toward the circulator 218.

[0034] The higher the tuning quality, the higher the standing wave quality, the more energy is stored in the waveguide 202, and the stability and performance of the resonant cavity are improved. If the tuning quality is poor, the standing wave quality will be poor, energy will be wasted, less energy will be transferred to the accelerated electrons, and the quality of the terminal treatment beam 210 will be poor. Thus, if the treatment beam quality is poor, the patient treatment may be substandard. Therefore, if the quality of the automatic frequency control (AFC) 220 is reduced, it may result in poor patient treatment quality, for example, the dose rate may deviate from the patient treatment plan.

[0035] Any suitable type of automatic frequency control may be employed, such as a feedback controlled tuner. The AFC system 220 may include a phase detector to compare samples of the forward and reflected RF waves, which may be used to obtain an error signal representing a frequency deviation between the RF power source 214 and the resonant frequency of the waveguide 202. The AFC system 220 may also include a servo loop that senses the output of the phase detector and drives a tuner to tune the frequency of the RF power source to the frequency of the resonant cavity 202 of the waveguide. The tuner may be a mechanical electromechanical tuner. The skilled person will appreciate that any other suitable type of AFC may be employed, such as an injection locked or reflection system.

[0036] AFC system 220 receives samples of the forward RF wave via RF transmission link 224. In some embodiments, Figure 2, link 224 is located directly between RF power source 214 and AFC system 220. Link 224 may be located between AFC system 220 and any portion of a first portion of RF transmission device 216a that couples circulator 218 and RF power source 214. Due to the operation of circulator 218, as described above, only forward RF waves are present in portion 216a of the RF transmission device.

[0037] The AFC system receives samples of the reflected RF waves via RF transmission link 228. In some embodiments, Figure 2 , link 228 is located directly between waveguide 202 and AFC system 220. Whether a three-port circulator or a four-port circulator is used, link 228 is typically located between AFC system 220 and the third port of circulator 218. By using a circulator, the AFC receives only reflected waves via RF transmission link 228. Link 226 represents an AFC tuner that changes the frequency of RF power source 214 to tune it to the waveguide resonant frequency.

[0038] Known automatic frequency control systems measure the degree of frequency deviation using methods that are inherently frequency and / or amplitude related. For example, the phase difference measured by the phase detector (indicative of the degree of frequency deviation) is frequency and / or amplitude related. It is for this reason that the AFC system needs to be calibrated to the desired frequency in order to work optimally. If the waveguide resonant frequency drifts too far from its initial calibration value, the quality of the AFC may degrade. The resonant frequency drift is caused by factors such as aging and temperature changes. After a certain amount of drift, the AFC tuning quality may be reduced, the standing wave quality may be reduced, energy may be wasted, less energy will be transferred to the accelerated particles, and the quality of the terminal treatment beam 210 will also be reduced.

[0039] The present disclosure relates to systems and methods for quantifying whether AFC quality is within an acceptable operating range. If not, corrective action can be taken to adjust the AFC back to a good quality state.

[0040] Figure 3 Draw out Figure 2 The components of the present invention are combined with an AFC quality assurance system 300 according to the present disclosure. The AFC quality assurance system 300 quantifies the quality of the automatic frequency control, identifies whether the AFC quality has degraded, and recommends or implements corrective actions. The AFC quality assurance system 300 is a system that monitors the automatic frequency control between the RF power source and the waveguide.

[0041] The AFC quality assurance system 300 includes an RF diode detector 302, an oscilloscope 304, and a computer 306 including a processor and a memory. The RF diode detector 302 can be of any suitable type, such as a Narda 503A. The RF diode detector 302 is connected to an RF coupling probe port at the third port of the circulator 218. The output of the diode detector 302 is connected to a channel of the oscilloscope 304 so that the oscilloscope can monitor the reflected RF wave. The reflected power load 222 absorbs the reflected wave power, and the diode detector 302 samples the reflected wave amplitude. The diode detector 302 can sample the reflected wave amplitude through the coupling probe, which can include a built-in attenuator. As described above, the circulator 218 ensures that only RF (i.e., reflected RF waves) incident from the waveguide can exit via the third port. The diode detector is configured to detect RF pulses reflected from the waveguide through the circulator.

[0042] The oscilloscope 304 can display the reflected RF wave received via the diode detector 302 as a waveform diagram based on time and amplitude. The oscilloscope can be configured to display a waveform, wherein the waveform is an RF pulse reflected from a waveguide. The amplitude represents a voltage proportional to the pulse power. Any oscilloscope or suitable equivalent system can be used as long as the oscilloscope or system is capable of performing the following tasks: pass / fail testing, defining a pass / fail mask area (within a certain time window and amplitude range), and reading out pass / fail statistics. Pass / fail testing is a standard function of modern digital oscilloscopes, and the pass / fail test determines whether one or more waveforms meet a set of predefined criteria. The predefined criteria can include defining a pass / fail mask area on the oscilloscope. The mask area is a two-dimensional area that is generally rectangular and defined by the dimensions of time and amplitude (power / voltage). Therefore, the mask area can be defined by two ranges: the time range between a first time point (left edge) and a second time point (right edge), and the voltage (power) range between a first voltage (lower edge) and a second voltage (upper edge). In Figure 5a and Figure 5b 502. The pass / fail mask test can compare the sampled values ​​of a waveform with the mask to test whether the waveform covers the mask. In other words, the pass / fail mask test determines whether the waveform falls at least partially within the mask or completely outside the mask.

[0043] The oscilloscope 304 defines a fail and a pass in a pass / fail mask area test as follows: if the waveform covers the mask area (i.e., the waveform is at least partially within the mask area), the oscilloscope outputs a "pass"; if the waveform does not cover the mask area (i.e., the waveform is completely outside the mask area), the oscilloscope outputs a "fail". For other oscilloscopes or equivalent systems, the definitions of "fail" and "pass" in a pass / fail mask area test may be interchanged so that: if the waveform covers the mask area (i.e., the waveform is at least partially within the mask area), the oscilloscope outputs a "fail"; if the waveform does not cover the mask area (i.e., the waveform is completely outside the mask area), the oscilloscope outputs a "pass". Some oscilloscopes may have the ability to switch between "fail" and "pass" criteria. The skilled person should recognize that it is not a requirement that the oscilloscope define "fail" and "pass" in a certain manner, as "fail" and "pass" are labels that can be directly switched through further processing.

[0044] The predefined criteria for the pass / fail test may alternatively include defining a threshold amplitude. The threshold amplitude may be set regardless of time, or may be set only for a defined time window (i.e., between a start time and an end time). Thus, the time window threshold amplitude may be defined by three values: a start time point, a second time point, and an amplitude threshold. The pass / fail threshold test may compare the sampled values ​​of a waveform with a threshold to test whether the waveform exceeds the threshold within a defined time window. If the waveform exceeds the threshold at any point within the time window, the oscilloscope outputs "pass"; if the waveform does not exceed the threshold at any point within the time window, the oscilloscope outputs "fail".

[0045] As described above, the oscilloscope or equivalent system must be capable of performing a pass / fail statistical readout in order to be suitable for use in the AFC quality assurance system 300. The pass / fail statistical readout is a count of waveforms that failed and passed a pass / fail test (pass / fail mask area test or pass / fail threshold test), which is output by the oscilloscope to the oscilloscope display and / or the memory of the computer 306. For the pass / fail mask area test, the pass / fail threshold test is recorded in the oscilloscope display. Figure 5a and Figure 5b The readout pass / fail statistics 504a, 504b are displayed on the oscilloscope display in FIG.

[0046] Examples of suitable oscilloscopes include the Rigol DS1000 series and the Siglent SDS1000 series. The oscilloscope 304 is connected to the computer system wirelessly or using a wired connection. The computer may include a processor and a memory.

[0047] The processor may be configured to transmit data to other computing devices, which may be connected to each other (e.g., networked) and / or to other machines in a local area network (LAN), an intranet, an extranet, or the Internet. Each computing device may operate as a server or client machine in a client-server network environment, or as a peer machine in a peer-to-peer (or distributed) network environment. Each controller may be a personal computer (PC), a tablet computer, a set-top box (STB), a personal digital assistant (PDA), a cellular phone, a web appliance, a server, a network router, a switch or a bridge, or any machine capable of executing a set of (sequential or non-sequential) instructions specifying the actions to be taken by the machine.

[0048] In some embodiments, the AFC quality assurance system 300 can be detached and reattached to the radiation therapy device via an RF connection to the third circulator port.Alternatively, the AFC quality assurance system 300 can be fully integrated into the radiation therapy device.

[0049] Reference now Figure 4 The method of the present disclosure is depicted in the flowchart 400 of FIG. Figure 5a and Figure 5b Two exemplary reflection waveforms are plotted in FIG.

[0050] Figure 4 A method according to the present disclosure is shown. The method is performed by an oscilloscope 304 (or equivalent system) and a computer 306 including a processor and a memory. In some embodiments, the method may require manual input from a user. In other embodiments, the entire method can be configured to run automatically. Method 400 can be used to monitor an RF power source and automatic frequency control between the waveguide.

[0051] Method 400 is performed in part or in whole by a processor having a computer-readable medium, which, when executed by the processor, causes the processor to perform some or all of the methods disclosed herein. The medium may be a non-transitory computer-readable medium. The term "computer-readable medium" as used herein refers to any medium storing data and / or instructions for causing a processor to work in a particular manner. Such storage media may include non-volatile media and / or volatile media. Non-volatile media may include, for example, optical disks or magnetic disks. Volatile media may include dynamic memory. Exemplary forms of storage media include floppy disks, floppy disks, hard disks, solid-state hard disks, tapes or any other magnetic data storage media, CD-ROMs, any other optical data storage media, any physical media with one or more hole patterns, RAMs, PROMs, EPROMs, FLASH-EPROMs, NVRAMs, and any other storage chips or reel-to-reel tapes.

[0052] The method begins at step 410. At step 410, a waveform representing an RF pulse reflected from the waveguide 202 is received. That is, the method 400 includes receiving a waveform of an RF pulse reflected from the waveguide. Step 410 may be implemented using a diode detector 302 to detect the RF pulse reflected from the waveguide. As described above, the circulator 218 and the reflected power load 222 ensure that the diode detector 302 detects only reflected RF waves. The detected reflected RF wave may be received at an oscilloscope 304 or equivalent system, and the received information represents a waveform diagram (time and amplitude information).

[0053] Step 410 may also include: drawing the waveform on a graph. For example, the oscilloscope 304 may display a waveform based on time and amplitude (power / voltage) on the oscilloscope display. The oscilloscope 304 may be configured so that a single complete reflection waveform is captured clearly and stably on the oscilloscope display. This is achieved by setting the horizontal time base, vertical coordinate, trigger mode, trigger edge, and trigger level to appropriate values. The oscilloscope may be automatically configured or manually configured by the user.

[0054] The reflected waveform received at step 410 has a typical "rabbit ear" shape. The rabbit ear shape includes the following sequential graphical features: first falling edge (line segment with negative gradient), first minimum point, first rising edge (line segment with positive gradient), first maximum point, second falling edge (line segment with negative gradient), stationary point, third falling edge (line segment with negative gradient), second minimum point, and finally second rising edge (line segment with positive gradient). The first maximum point is the minimum reflected power point. If there is a perfect standing wave in the waveguide 202, there should be zero power at the minimum reflected power point based on perfect constructive and destructive interference and perfect storage of energy in the waveguide.

[0055] Figure 5aAn exemplary reflected RF waveform displayed on a Rigol DS1102-E oscilloscope is plotted. The waveform is based on a time versus amplitude plot, where the amplitude is voltage, time is displayed in units of 1 μs, and voltage is displayed in units of 50 mV. The oscilloscope has been manually configured to stably capture and display a complete reflected waveform.

[0056] The reflected waveform 500a has a typical rabbit ear shape including the above-mentioned graphical features: a first falling edge (508a), a first minimum point (510a), a first rising edge (512a), a first maximum point (506a), a second falling edge (514a), a stagnation point (516a), a third falling edge (518a), a second minimum point (520a), and finally a second rising edge (522a).

[0057] The pulse width of the reflected waveform 500a is about 5.5 μs, which corresponds to an RF pulse duration of 5.5 μs, i.e., a nominal pulse width of 5.5 μs. The waveform 500a reaches a maximum voltage of about 0 V and a minimum voltage of about -200 mV. The pulse width of 5.5 μs is defined from the middle of the first falling edge 508a and the second rising edge (522a).

[0058] Reference again Figure 4 . At step 420, a tuning mask region is defined on the waveform diagram. That is, the method 400 further includes: defining a tuning mask region on the waveform diagram. Step 420 can be implemented by the oscilloscope 304 or a suitable equivalent system. The mask region is a two-dimensional region that is generally rectangular and defined in terms of time and amplitude (power / voltage). As described above, the mask region can be defined by two ranges: a time range between a first time point (left edge) and a second time point (right edge), and a voltage (power) range between a first voltage (lower edge) and a second voltage (upper edge).

[0059] The tuning mask region is configured to capture the minimum reflected power point on the reflected waveform, i.e., the point on the waveform where the waveform amplitude is the smallest. The tuning mask region is defined so that if the tuning requirements are met, the minimum reflected power point should cover the tuning mask region. The tuning requirements are defined based on the amount of tuning (i.e., frequency matching) required between the RF power source 214 and the waveguide 202. The tuning requirements depend on factors such as the manufacturer and model of the radiotherapy equipment, the age of the radiotherapy equipment, the temperature of the waveguide 202, and the user's requirements for the required automatic frequency control quality level.

[0060] The minimum reflected power point (e.g., minimum reflected power point 506a of waveform 500a) directly follows the waveguide energy fill time on the waveform (524a of waveform 500a). The waveguide energy fill time (initial fill phase) is a time period starting at the start of the waveform during which energy from the RF power source is transferred to the standing wave guide. The electron source 204 is configured such that there are no accelerated electrons during the waveguide energy fill time. As an example, for a standing wave guide with a Q value of 15,000 and a resonant frequency of 2,998 MHz, the waveguide energy fill time is approximately 0.6 μs. The electron source 204 is configured to inject electrons during a time period within the RF pulse. The waveform 500a was captured without beam loading in the waveguide, so there would be no accelerated electrons in this example. If the beam loading were to be turned on, there would be accelerated electrons during time period 530a.

[0061] In order to define a tuning mask region suitable for the minimum reflected power point to be covered therein, the first voltage value is set to a value substantially equal to 0 V. The first voltage value may also be set to 0 V (i.e., at ground level). The first voltage value set to 0 V represents an ideal case of frequency matching between the RF frequency at the RF power source 214 and the resonant frequency of the waveguide 202, wherein the RF power source power is fully absorbed by the waveguide at the minimum reflected power point.

[0062] If the waveguide 202 cannot absorb all the RF energy in the initial filling stage and the first voltage value can be set to below 0V based on the tuning requirements of the AFC, the first voltage value can be set to below 0V. That is, the first voltage value depends on the required AFC quality and sets the allowed AFC quality tolerance. In one example, the first voltage value can be set to 1% of the first maximum voltage value of the received waveform. That is, the first voltage value can be set to 1% of the value of the first minimum point. Figure 5a and Figure 5b In the example of FIG. 5 , the value of the first minimum point 510 a , 510 b is −200 mV, so the first voltage value may be set to −2 mV.

[0063] The better the desired automatic frequency control tuning quality between the RF power source and the waveguide, the closer the first voltage value is set to 0 V. The second voltage value is set to any value greater than 0 V. For example, a second voltage value of 3 V can be arbitrarily selected. As an example, waveform 500a has a tuning mask region 502 (shaded rectangular region) having a first voltage value (lower edge) of -2 mV and a second voltage value (upper edge) of 100 mV.

[0064] As described above, the tuning mask region is also defined in time. The first time point of the tuning mask region is before the end of the waveguide energy fill time. Equivalently, the first time point is before the beginning of the time period in which accelerated electrons will appear. The first time point of the tuning mask region is between the beginning of the first falling edge of the waveform and the first maximum point of the waveform. For example, waveform 500a has a tuning mask region 502 (shaded rectangular region) that has a first time point (the leftmost edge of the shaded rectangular region) that is after the first falling edge of the waveform but before the first maximum point of the waveform.

[0065] The second time point of the tuning mask area is the first time point plus the "offset range". The offset range can be a predetermined value or a predetermined percentage value. The offset range is a time range configured to accommodate the allowable degree of difference between received waveforms. The offset range should be long enough to cover the standard differences between waveforms caused by factors such as noise and temperature fluctuations. The offset range should be short enough to avoid recording waveforms that are unacceptable as complete normal pulses in terms of delivering enough energy to the waveguide and electron beam. In other words, if the offset range is too long, a waveform with a later rising edge may be suitable as a usable pulse. A pulse with a later rising edge means that a usable pulse with a narrower width is provided to the electron beam. What the technician should realize is that the RF pulse needs to be close to the correct length in order to contain enough RF energy.

[0066] A reasonable value for the offset range is 10% of the RF pulse duration. For example, for a 5 μs pulse, a reasonable value for the offset range is 0.5 μs. The second time point of the tuning mask region is usually after the waveguide energy fill time. The tuning mask region 502 has a second time point (the rightmost edge of the shaded rectangular region) that is the first time point plus the offset range. The duration of the pulse / waveform 500a is approximately 5.5 μs, so the offset range is 0.55 μs.

[0067] A skilled person may infer from the above description that defining a tuning mask region may include defining a first voltage value between a first time point and a second time point. Since the second voltage value is arbitrary, this value may not be required to define the tuning mask region.

[0068] At step 430, if the waveform covers the tuning mask area, an indication that the tuning requirements are met is output. That is, method 400 may further include: if the waveform covers the tuning mask area, an indication that the tuning requirements are met is output. In some examples, if the waveform does not cover the tuning mask area, an indication that the tuning requirements are not met is output.

[0069] Outputting a positive indication may include outputting "pass", while outputting a negative indication may include outputting "fail." Step 430 may be implemented by a processor that is part of a computer or oscilloscope 304. As described above, the oscilloscope may employ a pass / fail mask test.

[0070] For the exemplary waveform 500a, the waveform covers the tuning mask area, so a positive indication is output. In this example, a pass / fail mask area test is performed by an oscilloscope, so a "pass" is output.

[0071] At step 440, steps 410 to 430 may be repeatedly performed for a plurality of waveforms within a defined time period, the plurality of waveforms representing RF pulses reflected from the waveguide. That is, for each of the plurality of waveforms, the method may include: receiving a waveform of an RF pulse reflected from the waveguide; drawing the waveform on a graph; defining a corresponding tuning mask region; determining whether the waveform covers the corresponding tuning mask region; if the waveform covers the tuning mask region, outputting a positive indication that the tuning requirement is met, and if the waveform does not cover the tuning mask region, outputting a negative indication that the tuning requirement is not met.

[0072] For each of the plurality of waveforms, the tuning mask region typically maintains the same rectangular shape having dimensions of constant voltage and time (relative to the time of each new waveform) throughout the time period. Defining the current tuning mask region may include defining the tuning mask region based on the waveform in question. The defined time period during which the plurality of waveforms are received and analyzed may be considered a test time period. The oscilloscope is still configured to stably capture and clearly display a complete reflected waveform.

[0073] Figure 5b An exemplary reflected RF waveform displayed on an oscilloscope screen is plotted, with waveform 500b being received during the same test period as waveform 500a. The oscilloscope configuration remains unchanged for both waveforms 500a and 500b: time is displayed in units of 1 μs, while voltage is displayed in units of 50 mV. The length of reflected waveform 500b is approximately 5.5 μs, which corresponds to an RF pulse duration of 5.5 μs, the same as waveform 500a, as expected. Reflected waveform 500b has the same typical rabbit ear shape as waveform 500a.

[0074] The reflected waveform 500b has a typical rabbit ear shape, including similar graphical features to the waveform 500a: a first falling edge (508b), a first minimum point (510b), a first rising edge (512b), a first maximum point (506b), a second falling edge (514b), a stagnation point (516b), a third falling edge (518b), a second minimum point (520b) and finally a second rising edge (522b).

[0075] The minimum reflected power point (i.e., the first maximum point 506b) directly follows the waveguide power fill time. Waveform 500b was captured without beam loading in the waveguide, so there would be no accelerated electrons in this example. If beam loading were to be turned on, there would be accelerated electrons in time period 530b.

[0076] Waveform 500b has the same associated tuning mask region 502 (shaded rectangular region) as waveform 500a: the first voltage value (lower edge) is -2 mV, the second voltage value (upper edge) is 100 mV, the first time point is equal to the first time point of waveform 500a plus (n+1) (the time between pulses), and the second time point is equal to the second time point of waveform 500a plus (n+1) (the time between pulses), where n is the number of pulses / waveforms received between waveform 500a and waveform 500b.

[0077] Waveform 500b reaches a maximum voltage of about -8 mV and a minimum voltage of about -200 mV. The maximum voltage of waveform 500b (corresponding to the minimum reflected power point) is different from waveform 500a because waveform 500b does not cover the tuning mask area. Therefore, at step 430 for waveform 500a, a negative indication that the tuning requirements are not met is output. Since the oscilloscope performs a pass / fail mask area test for waveform 500b, a "fail" is output.

[0078] When the defined time period of step 440 ends, steps 410 to 430 stop repeating, and the method continues at step 450. At step 450, a ratio of positive indications (or "passes") and negative indications (or "failures") may be defined. A total count of all "passes" and "failures" may also be calculated and / or output. Step 450 may be implemented by oscilloscope 304 or a suitable equivalent system.

[0079] For the oscilloscope 304, step 450 may output the pass / fail statistics to the oscilloscope display and / or the memory of the computer 306. By turning on the pass / fail statistics display, the pass / fail statistics may be viewed. Figure 5a and Figure 5b The readout pass / fail statistics display 504a, 504b can be seen on the oscilloscope display of FIG. The pass / fail statistics display shows the number of passes, the number of fails, and the total number of waveforms, the number of waveforms being denoted as wfs.

[0080] The pass / fail statistics can be used to calculate a ratio of "passes" to "failures." This can be performed by reading the statistics out to a memory of computer 306 so that the computer processor can calculate the ratio. At the time waveform 500b was captured, the pass / fail ratio was 0.074.

[0081] At step 460, the ratio calculated in step 450 is compared to a predefined threshold to determine whether the RF power source is tuned to the waveguide resonant frequency. The threshold is set according to a predefined quality requirement, which may depend on factors such as the manufacturer and model of the radiotherapy device, the age of the radiotherapy device, the user-defined quality requirements, the temperature of the waveguide, and whether there is beam loading. If the ratio calculated at step 450 meets or exceeds the threshold ratio, the RF power source is tuned to the waveguide resonant frequency to meet the predefined quality requirement. Thus, the automatic frequency control operates within the predefined quality requirement range.

[0082] The method 400 may further include step 470. If the RF power source is not tuned to the waveguide resonant frequency, corrective actions may be taken to recalibrate the automatic frequency control. The corrective actions may involve online AFC setting adjustments, such as recalibration of frequency settings, or offline quality assurance service intervention. At step 470, a real-time notification may be sent to a clinician notifying the clinician that the AFC quality may have degraded. The notification may suggest appropriate corrective actions to the clinician to improve the AFC quality.

[0083] It should be understood that the above description of specific embodiments is exemplary only and is not intended to limit the scope of the present disclosure. Many modifications of the described embodiments are contemplated and should be within the scope of the present disclosure. Some of these modifications will now be described.

[0084] Figure 5a and Figure 5b Two exemplary waveforms are plotted, both of which exhibit a typical rabbit ear shape. In some embodiments, the "rabbit ear" shape can be reversed when a reverse polarity voltage measurement is made. Depending on the polarity type of the diode detector, the rabbit ear shape can be of opposite polarity. For example, the Narda 503A has a negative polarity, while the 503A-03 has a positive polarity. The method of the present invention can be directly applicable to opposite polarities. If the polarity of the voltage measurement is negative, the waveform is defined by negative voltage values; and the first voltage value is 0V or a negative voltage value. If the polarity of the voltage measurement is positive, the waveform is defined by positive voltage values; and the first voltage value is 0V or a positive voltage value.

[0085] There may also be variations in the typical rabbit ear shape due to factors such as the make and model of the radiotherapy device, the age of the radiotherapy device, the temperature of the waveguide 202, and the presence or absence of beam loading. Figure 5a and Figure 5bThe waveform is plotted without beam loading. The shape of the rabbit ear waveform may change with the presence of beam loading, especially the portion of the waveform where accelerated electrons are present, such as time period 530a and time period 530b. The method of the present disclosure is equally applicable to waveguides with beam loading, as the RF energy fill phase is the same in both scenarios.

[0086] The method of the present disclosure 400 leads to defining a tuning mask region to detect the minimum reflected power point on the waveform and thus determine whether the resonant frequency of the RF power source 214 and the waveguide 202 meets the tuning requirements and is frequency matched. Depending on the desired operation, the tuning mask region defined in step 420 can be dynamically defined to change the dimensions of the tuning mask region to evaluate the AFC quality against different thresholds at different time points.

[0087] In some embodiments, waveform analysis can be performed by computer 306 without defining a tuning mask region, but instead a threshold can be set on a waveform similar to the first voltage value described in method 400. If the waveform exceeds the threshold, the tuning requirement is met. Alternatively, computer 306 can use graphical analysis software to identify turning points on the waveform to find the minimum reflected power point. The minimum reflected power point can then be compared to the threshold. The threshold is set to 0V (i.e., at ground level) or a value slightly less than 0V, such as -2mV. If waveguide 202 cannot absorb all of the RF energy during the initial filling stage and the threshold can be set to less than 0V based on the tuning requirements, the threshold can be set to less than 0V. The better the automatic frequency control tuning quality required between the RF power source and the waveguide, the closer the threshold is set to 0V.

[0088] Advantageously, the method 400 of the present disclosure provides a system for evaluating the quality of automatic frequency control in a quantitative manner. By directly measuring the reflected RF power from the waveguide, direct monitoring of the quality of automatic frequency control is achieved. The method 400 and the AFC quality assurance system 300 avoid the use of indirect measurements (such as analyzing radiation dose rate changes or using algorithms to characterize and monitor AFC). According to the present disclosure, AFC quality assurance can be tested at any time, regardless of beam loading. In contrast, indirect measurements such as radiation dose rate change measurements can only be performed in the presence of beam loading.

[0089] Advantageously, the disclosed method is not dependent on the RF power source or the waveguide resonant frequency. This is particularly beneficial in situations where the RF resonant frequency has drifted significantly from the initial calibration value of the AFC 220.

[0090] Method 400 and AFC quality assurance system 300 can be applied to routine daily monitoring of AFC quality to avoid degradation of the beam quality delivered to the patient. The type of AFC system does not affect the results, and the method can also be applied to any form of AFC, such as phase-based feedback loops, injection locking or reflection systems.

[0091] The method 400 and the AFC quality assurance system 300 can also be used as an AFC quality benchmarking tool, which will be used to compare the performance of different AFC methods. The AFC quality assurance system 300 can be easily attached to and detached from the radiotherapy equipment, thereby providing the opportunity to use one system 300 to check the AFC quality of multiple radiotherapy equipment in one facility. The simple installation also reduces the time required for maintenance personnel. The AFC quality assurance system 300 does not interfere with the operation of the radiotherapy equipment. The computer system 306 can allow online real-time monitoring of AFC quality and can signal the clinician when the AFC quality deteriorates.

[0092] It should be understood that the above description is illustrative rather than restrictive. After reading and understanding the above description, many other embodiments will be apparent to those skilled in the art. Although the present disclosure has been described in conjunction with specific exemplary embodiments, it should be appreciated that the present disclosure is not limited to the described embodiments, but can be practiced by modification and change within the spirit and scope of the appended claims. Therefore, this specification and the accompanying drawings should be regarded as illustrative rather than restrictive. Therefore, the scope of the present disclosure should be determined with reference to the appended claims and the full scope of equivalents to which these claims are entitled.

Claims

1. A method for monitoring automatic frequency control between a radio frequency power source and a waveguide, the method comprising: receiving a waveform of a radio frequency pulse reflected from the waveguide; drawing the waveform on a waveform graph; A tuning mask area is defined on the waveform diagram; wherein the tuning mask area includes a two-dimensional area defined by a time range between a first time point and a second time point and a voltage or power range between a first voltage value and a second voltage value; the tuning mask area is defined such that if a tuning requirement is met, the minimum reflected power point on the waveform can cover the tuning mask area; as well as If the waveform covers the tuning mask region, an indication that the tuning requirements are met is output.

2. The method according to claim 1, wherein: The first voltage value is equal to zero volt or less than zero volt.

3. The method according to claim 1, wherein: The first voltage value is 1% of a first maximum voltage value of the received waveform.

4. The method according to any one of claims 1 to 3, wherein: The first time point is between the beginning of a first falling edge of the waveform and a first maximum value point of the waveform.

5. The method according to claim 4, wherein: The second time point is the time of the first time point plus an offset range, wherein the offset range is a predetermined value or a predetermined percentage value.

6. The method according to claim 5, wherein: The offset range is 10% of the RF pulse duration.

7. The method according to any one of claims 1 to 3, wherein: If the waveform does not cover the tuning mask region, an indication is output that the tuning requirements are not met.

8. The method according to any one of claims 1 to 3, further comprising, for each of the plurality of waveforms: receiving a waveform of a radio frequency pulse reflected from the waveguide; plotting the waveform on a graph; defining the corresponding tuning mask region; determining whether the waveform covers the corresponding tuning mask region; as well as If the waveform covers the tuning mask area, a positive indication that the tuning requirement is met is output; if the waveform does not cover the tuning mask area, a negative indication that the tuning requirement is not met is output.

9. The method according to claim 8, wherein: Defining the current tuning mask region includes defining the region based on the waveform in question.

10. The method according to claim 8, wherein: The method further includes defining a ratio of positive indications or "passes" to negative indications or "failures".

11. The method according to claim 10, wherein: The ratio is compared to a predefined threshold to determine whether the RF power source is tuned to the waveguide resonant frequency.

12. The method according to claim 11, wherein: If the RF power source is not tuned to the waveguide resonant frequency, corrective action is taken to recalibrate the automatic frequency control.

13. The method according to claim 8, wherein: Determining whether the waveform covers the corresponding tuning mask region includes determining whether a minimum power point on the waveform meets a defined threshold.

14. The method according to any one of claims 1 to 3, wherein: If the polarity of the voltage measurement is negative, then: The waveform is defined by negative voltage values; and The first voltage value is 0V or a negative voltage value, And wherein, if the polarity of the voltage measurement is positive, then: The waveform is defined by positive voltage values; and The first voltage value is 0V or a positive voltage value.

15. A system for monitoring automatic frequency control between a radio frequency power source and a waveguide, the system comprising: a diode detector configured to detect radio frequency pulses reflected from the waveguide by the circulator; an oscilloscope configured to display a waveform, wherein the waveform is a radio frequency pulse reflected from the waveguide; Processor; and A computer readable medium comprising computer executable instructions which, when executed by the processor, cause the device to: receiving a waveform of a radio frequency pulse reflected from the waveguide; drawing the waveform on a waveform graph; defining a tuning mask area on the waveform graph; wherein the tuning mask area includes a two-dimensional area defined by a time range between a first time point and a second time point and a voltage or power range between a first voltage value and a second voltage value; the tuning mask area is defined such that if a tuning requirement is met, a minimum reflected power point on the waveform can cover the tuning mask area; and If the waveform covers the tuning mask region, an indication that the tuning requirements are met is output.

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