An electronic FLASH radiotherapy beam-out control method, system and device

Abstract

This application relates to the field of radiotherapy dose control technology, and discloses an electronic FLASH radiotherapy beam emission control method, system, and device. The method includes: obtaining the target beam emission time based on the target dose and target dose rate; calculating the number of large pulses and the remaining dose based on a preset single large pulse dose; calculating the pulse width and the number of small pulses; determining the total number of pulses based on the number of large pulses and the number of small pulses, and calculating the beam emission pulse frequency based on the total number of pulses and the target beam emission time; executing a beam emission command based on the number of large pulses, the number of small pulses, the large pulse width, the small pulse width, and the beam emission pulse frequency; terminating pulse emission when any one of the following conditions is met: the cumulative pulse count equals a pulse count threshold, the cumulative dose is greater than or equal to the target dose, or the cumulative beam emission time is greater than or equal to a preset beam emission time. This application can control the radiotherapy dose rate evenly and accurately.

Description

Technical Field

[0001] This application relates to the field of radiotherapy dose control technology, and in particular to an electronic FLASH radiotherapy beam control method, system and device. Background Technology

[0002] Electron FLASH radiotherapy technology kills tumor cells and reduces toxic side effects on normal tissues by delivering ultra-high dose rates of electron beams over a very short time. In electron linear accelerators, the electron beam is typically generated in pulses. Current electron FLASH radiotherapy beam control schemes usually employ a combination of large pulses of fixed width and small pulses of fixed width. The actual beam termination mechanism is determined based on whether the dose monitoring value of the radiation monitoring system is greater than or equal to the termination dose threshold, whether the monitored actual beam termination time is greater than or equal to the termination time threshold, or whether the monitored number of pulses equals the termination pulse number threshold.

[0003] The existing technology has two drawbacks: First, in actual accelerator beam output, the dose of a single pulse may fluctuate slightly, which is normal. This is because the beam-stopping condition is reaching the beam-stopping dose threshold, the beam-stopping time threshold, or the number of beam-stopping pulses. The beam-stopping time threshold includes the beam output time and the reserved time margin, while the beam-stopping pulse number threshold includes the target number of pulses and the reserved number margin. Therefore, when the dose of a single pulse fluctuates, the number of pulses will change, resulting in a significant change in the total beam output time at a fixed frequency, thus causing a large fluctuation in the actual dose rate. Specifically, in actual accelerator beam output, when the dose of a single large pulse is too high, the cumulative dose of the large pulse will be too high. The number of small pulses required to reach the beam-stopping dose threshold of the radiation monitoring system will decrease, resulting in a decrease in the total number of pulses. At a given pulse frequency, the total beam output time will be shortened, leading to a higher actual overall dose rate. When the dose of a single large pulse is too small, the cumulative dose of the large pulse will be smaller, increasing the number of small pulses required to reach the dose threshold of the radiation monitoring system, thus increasing the total number of pulses. At a given pulse frequency, this prolongs the total beam egress time, resulting in a lower actual overall dose rate. Secondly, within each beam egress cycle, the large pulses in the early stages and the small pulses in the later stages lead to a much higher dose rate in the early stages, resulting in a severe imbalance in dose rates. Since the protective effect of FLASH radiotherapy has been proven to be dose rate-dependent, changes in dose rate may lead to a decrease in the efficacy of radiotherapy. Summary of the Invention

[0004] To address the problem of large overall dose rate fluctuations and uneven dose rates in the early and late stages caused by slight fluctuations in the dose of a single pulse in the existing technology, this application provides an electronic FLASH radiotherapy beam control method, system, and device. Even when any single pulse dose experiences random slight fluctuations, the total number of pulses and the beam exit time can still be kept strictly constant, thereby achieving extremely balanced and precise macroscopic dose rate control.

[0005] This application discloses a method for controlling the beam output of electronic FLASH radiotherapy, which includes: S1. Based on the target dose and target dose rate, obtain the target beam exit time; S2. Based on the preset single large pulse dose, calculate the number of large pulses and the remaining dose; S3. Based on the linear relationship between a single large pulse dose and a large pulse width, and the remaining dose, calculate the small pulse width and the number of small pulses, wherein the number of small pulses is 0 or 1; S4. Determine the total number of pulses based on the number of large pulses and the number of small pulses, and calculate the beam pulse frequency based on the total number of pulses and the target beam emission time; S5. Execute the beam output command based on the number of large pulses, the number of small pulses, the width of large pulses, the width of small pulses, and the output pulse frequency; S6. When any one of the following conditions is met: the cumulative number of pulses equals the pulse number threshold, the cumulative dose is greater than or equal to the target dose, or the cumulative beam emission time is greater than or equal to the preset beam emission time, pulse emission is terminated. The pulse number threshold is equal to the total number of pulses plus the number margin.

[0006] Further, S1 includes: The target beam exit time is obtained by dividing the target dose by the target dose rate.

[0007] Further, S2 includes: Divide the target dose by the preset single large pulse dose, and round the quotient down to get the number of large pulses; Calculate the total dose of all large pulses based on the number of large pulses and the dose of a single large pulse; The difference between the target dose and the large pulse dose is calculated to obtain the remaining dose.

[0008] Further, S3 includes: Based on the linear relationship between pulse dose and pulse width, using a preset single large pulse dose and large pulse width as a benchmark, and combining the remaining dose for proportional conversion, the small pulse width is derived in reverse.

[0009] Further, S4 includes: The total number of pulses is obtained by summing the number of large pulses and the number of individual small pulses. The total number of pulses is then divided by the target beam emission time, or by subtracting one from the total number of pulses and dividing by the target beam emission time, to obtain the beam emission pulse frequency.

[0010] Further, S6 includes: Monitor the cumulative number of pulses, cumulative beam time, and cumulative dose.

[0011] Furthermore, when the cumulative number of pulses equals the number of large pulses, the pulse width is adjusted to the small pulse width.

[0012] Furthermore, the preset beam-out time is equal to the target beam-out time plus a preset time margin.

[0013] This application also discloses an electronic FLASH radiotherapy beam control system, which includes a radiation control system, a radiation generation system, and a radiation monitoring system; The radiation control system is used to acquire the target dose and target dose rate, calculate the target beam emission time, and complete the calculation of the number of large pulses, the number of small pulses, the width of large pulses, the width of small pulses, the total number of pulses, and the beam emission pulse frequency; it sends the target dose and preset beam emission time to the radiation monitoring system, and sends the number of large pulses, the number of small pulses, the width of large pulses, the width of small pulses, the beam emission pulse frequency, and the beam emission command to the radiation generating system. The radiation generating system is used to execute beam emission commands based on the number of large pulses, the number of small pulses, the width of small pulses, and the frequency of emitted pulses. When any of the following conditions are met: the cumulative number of pulses equals the pulse number threshold, the cumulative dose is greater than or equal to the target dose, or the cumulative emission time is greater than or equal to the preset emission time, the radiation generating system terminates pulse emission. The pulse number threshold is equal to the total number of pulses plus the number margin. The radiation monitoring system is used to monitor the cumulative dose and cumulative beam emission time. When any of the following conditions are met, the cumulative dose is greater than or equal to the target beam emission dose and the cumulative time is greater than or equal to the preset beam emission time, the system outputs a beam stop command to the radiation generating system.

[0014] Furthermore, the radiation control system includes a controller and a storage module; The storage module is used to store preset large pulse dose, corresponding large pulse width, and linear relationship parameters between pulse dose and pulse width; The controller is used to calculate the target beam emission time based on the target dose and target dose rate, calculate the number of large pulses and the remaining dose based on the preset single large pulse dose, and then calculate the small pulse width in combination with the linear relationship to determine the total number of pulses and the beam emission trigger pulse frequency; send the target dose and preset beam emission time to the radiation monitoring system, and send the number of large pulses, the number of small pulses, the large pulse width, the small pulse width, the beam emission pulse frequency and the beam emission command to the radiation generation system.

[0015] Furthermore, when the cumulative number of pulses equals the number of large pulses, the radiation generating system adjusts the pulse width to a small pulse width.

[0016] Furthermore, the preset beam-out time is equal to the target beam-out time plus a preset time margin.

[0017] This application also discloses an electronic device including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, it implements the above-described electronic FLASH radiotherapy beam control method.

[0018] Due to the adoption of the above technical solution, this application has the following advantages: 1. Total Pulse Locking Mechanism: The beam output strategy is changed from "N large + many small" to "N large + 1 or 0 small". Even when the dose fluctuates in a single large pulse, the number of small pulses output during the actual beam output process is reduced by 1. The total number of pulses will only have a maximum deviation of 1 small pulse, which greatly improves the stability of the dose rate.

[0019] 2. Dynamic continuous pulse width adjustment technology: This technology breaks the limitation of fixed pulse width in traditional methods. By utilizing the linear range of accelerator beam characteristics, the width of the last pulse is dynamically adjusted through calculation to achieve precise control of dose and dose rate. This solves the problems of inaccurate dose rate control and high dose rate in the early stage and low dose rate in the later stage of the beam exit cycle in traditional methods.

[0020] 3. Extremely precise dose rate: Due to the constant total number of pulses and the strict locking of the total beam output time at a fixed frequency, even if the energy of a single pulse actually output by the accelerator fluctuates slightly (which is normal), the actual dose rate is highly consistent with the target dose rate.

[0021] 4. Very balanced dose rate: The beginning of the beam cycle consists of large pulses, while the last pulse is a small pulse. Furthermore, the beam frequency of the last pulse is consistent with the beam frequency of the large pulses, resulting in a very balanced dose rate throughout the entire beam cycle.

[0022] 5. Reduced system control frequency and hardware load: Compared to traditional solutions requiring a high-frequency trigger of 350Hz, this application only requires a trigger frequency of 150Hz. The significant reduction in pulse frequency effectively reduces switching losses in hardware such as the accelerator modulator and grid gun power supply, improving the reliability and lifespan of the equipment. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in the embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings.

[0024] Figure 1 This is a flowchart illustrating an electronic FLASH radiotherapy beam control method according to an embodiment of this application. Figure 2 This is a schematic diagram illustrating the relationship between pulse current and beam output time in an embodiment of this application; Figure 3 This is a schematic diagram of an electronic FLASH radiotherapy beam output control system according to an embodiment of this application. Detailed Implementation

[0025] The present application will be further described in conjunction with the accompanying drawings and embodiments. The described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments obtained by those skilled in the art should fall within the protection scope of the embodiments of the present application.

[0026] See Figure 1 This application provides an embodiment of an electronic FLASH radiotherapy beam control method, which includes: S1. Based on the target dose and target dose rate, obtain the target beam exit time.

[0027] Optionally, step S1 includes: The target beam exit time is obtained by dividing the target dose by the target dose rate.

[0028] S2. Based on the preset single large pulse dose, calculate the number of large pulses and the remaining dose.

[0029] Optionally, step S2 includes: Divide the target dose by the preset single large pulse dose, and round the quotient down to get the number of large pulses; Calculate the total dose of all large pulses based on the number of large pulses and the dose of a single large pulse; The difference between the target dose and the large pulse dose is calculated to obtain the remaining dose.

[0030] S3. Based on the linear relationship between a single large pulse dose and a large pulse width, and the remaining dose, calculate the small pulse width and the number of small pulses, wherein the number of small pulses is 0 or 1.

[0031] When the remaining dose is 0, the number of small pulses is 0; when the remaining dose is not 0, the number of small pulses is 1.

[0032] Optionally, S3 includes: Based on the linear relationship between pulse dose and pulse width, a small pulse width is derived by using a preset large pulse dose and pulse width as a benchmark and proportionally converting it to the remaining dose. Optionally, to ensure sufficient dose, the small pulse width can be rounded up.

[0033] S4. Determine the total number of pulses based on the number of large pulses and the number of individual small pulses, and calculate the beam pulse frequency based on the total number of pulses and the target beam emission time.

[0034] Optionally, S4 includes: The X-ray control system uses the sum of the number of large pulses and the number of individual small pulses as the total number of pulses, and divides the total number of pulses by the target beam emission time to obtain the beam emission pulse frequency.

[0035] Alternatively, subtract one from the total number of pulses and divide by the target beam emission time to obtain the beam emission pulse frequency.

[0036] S5. Execute the beam output command based on the number of large pulses, the number of small pulses, the width of large pulses, the width of small pulses, and the output pulse frequency.

[0037] Optionally, the radiation generating system performs pulsed beam emission based on the number of large pulses, the number of small pulses, the width of the large pulse, the width of the small pulse, and the output pulse frequency, including: After receiving the beam output command from the radiation control system, the radiation generation system outputs three synchronous electrical pulses from the FPGA-based central timing board, which respectively trigger the electron gun, klystron, and microwave excitation power source to work. The modulator power supply releases the energy stored in the capacitor, which is then used by the transformer to generate a high-voltage pulse for the klystron, thereby driving the klystron to generate a high-current electron beam. The microwave excitation power source outputs a reference microwave pulse. The high-current electron beam and the reference microwave pulse are converted into megawatt-level microwave pulses in the klystron and transmitted to the accelerating tube through a rectangular waveguide filled with sulfur hexafluoride gas. The electron gun emits an electron beam and pre-accelerates it to a preset speed before injecting it into the accelerating tube. The electron beam current must fall within the stable operating range of the microwave pulse. Microwave pulses excite an axial alternating electric field inside the accelerating tube, keeping the electron beam at the peak of the accelerating phase. Through the relay action of multiple accelerating cavities, it continuously acquires kinetic energy and finally forms a high-energy electron beam. The beam exits from the end of the accelerating tube and is successively broadened by a scattering foil and constrained by a light-limiting tube to form a uniformly distributed electron line. The beam is then emitted as a single pulse by the radiation generation system. The X-ray generating system completes the output of all large pulses according to the set pulse width. After all the large pulses are output, the central timing board sends a command to the electron gun to adjust the output pulse width and execute the output of a single small pulse. Each time the X-ray generating system emits a trigger pulse, the forward counter in the central timing board accumulates the pulse to be emitted, and the actual pulse detected by the pulse switch circuit is accumulated by the backward counter. The two count values ​​are compared in real time within each pulse cycle, and only the pulses that are deemed valid are used to participate in the cyclic beam output until all preset pulses are output.

[0038] S6. When any of the following conditions are met: the cumulative number of pulses equals the pulse number threshold, the cumulative dose is greater than or equal to the target dose, or the cumulative beam emission time is greater than or equal to the preset beam emission time, pulse emission is terminated. The pulse number threshold is equal to the total number of pulses plus the number margin.

[0039] Under ultra-high dose rate (e.g., FLASH radiotherapy) beam exit conditions, since the dose carried by a single pulse is extremely high and the beam exit time is extremely short (usually in milliseconds or sub-milliseconds), this embodiment constructs a multi-fault-tolerant protection network by introducing a redundancy and independent triggering mechanism for three dimensions: pulse counting, dose integration, and beam exit timing. Even if one of the monitoring dimensions lags or fails, the other dimensions can still respond quickly and trigger beam stop.

[0040] The output limit of the beam is strictly locked from three dimensions: time, number of pulses, and dose, eliminating the risk of excessive dose under ultra-high dose rate beam output conditions.

[0041] When the dose of a single large pulse is too high, the beam can be stopped before the total number of pulses has been exhausted because the cumulative dose in the termination condition has reached the target dose. In the existing beam-emission strategy of N1 large pulses + N2 small pulses, the single pulse dose of the small pulses is extremely small. In order to ensure that the dose does not exceed the limit, multiple small pulses will fail to be emitted. However, in the beam-emission strategy of N large pulses + 1 or 0 small pulses in this scheme, and the termination strategy based on dose, preset beam-emission time, and pulse number threshold, the single pulse dose of the small pulses in this scheme is larger than that of the small pulses in the existing technology. When the dose of a single large pulse is too high, at most only 1 small pulse will fail to be emitted. Therefore, the cumulative number of pulses will decrease by at most 1 small pulse. Compared with the existing technology, the dose rate stability is greatly improved.

[0042] When the dose of a single large pulse is too small, the number of pulses in this scheme is limited by the pulse number threshold in the beam stop condition. Also, since the single pulse dose of the small pulse in this scheme is larger than that of the small pulse in the prior art, the number of additional pulses will be at most a margin of 1-2 when the dose of a single large pulse is too small. In the beam output strategy of N1 large pulses + N2 small pulses used in the prior art, multiple small pulses will be generated in order to ensure that the dose meets the standard. Therefore, the dose rate stability is greatly improved compared with the prior art.

[0043] The radiation monitoring system monitors the cumulative dose and cumulative beam exit time in real time and outputs a beam stop signal, including: The radiation monitoring system is equipped with two independent ionization chambers. Each ionization chamber receives electron beams output from the radiation generation system. The electron beams ionize the gas inside the ionization chamber and generate an ion current, which is proportional to the instantaneous dose rate. The ion current of each ionization chamber is amplified by a signal amplification circuit and sent to an independent integrator. The output dose value is calculated in real time. The high-speed hardware comparator inside the ionization chamber continuously compares the output dose value with the target dose value. When the output dose value in any ionization chamber is greater than or equal to the target dose value for the first time, the comparator in the ionization chamber outputs a beam stop signal to the radiation generation system, so that the radiation generation system stops outputting the beam.

[0044] The radiation monitoring system is equipped with a timer. The target beam emission time is superimposed with a preset time margin to form a total time limit. The timer monitors the cumulative beam emission time. When the cumulative beam emission time reaches the total time limit, a beam stop signal is independently output to the radiation generation system to stop the radiation generation system from emitting beams.

[0045] For each trigger pulse emitted by the X-ray generation system, the forward counter increments the corresponding pulse count. The pulse switching circuit detects the actual discharge waveform through a current transformer. After the waveform is shaped, the backward counter increments the actual pulse count. The two counters verify the count value in real time within each pulse cycle. If the count values ​​match perfectly, the pulse is determined to be a valid pulse. This is used to count the actual number of beams emitted. Only valid pulses participate in the cyclic beam emission until all preset pulses are output, at which point a beam stop signal is output.

[0046] The beam-stop signal output from the ionization chamber, the beam-stop signal output after the forward and backward counters calculate the actual pulse, and the beam-stop signal output after the timer counts all enter the beam-out enable control logic gate circuit of the central timing board. Under normal conditions, the enable terminal is kept at a high level, allowing trigger pulse transmission. When any beam-stop signal is received, the enable terminal is immediately pulled low without delay, blocking the transmission of the trigger pulse to the pulse switch drive stage, terminating the generation of the electrical pulse signal of the solid-state modulator, thereby terminating further operation of the klystron, microwave excitation source, and electron gun, and the beam output stops within the same cycle. The radiation control system synchronously latches the trigger source and outputs a stop prompt through the human-machine interface.

[0047] The following specific example illustrates the implementation process of the method in this application: This application abandons the traditional approach of "completing with multiple fixed-width small pulses" and innovatively proposes a control architecture of "N fixed large pulses + 1 small pulse with adjustable width".

[0048] After calculating the remaining dose that needs to be supplemented, the radiation control system no longer breaks it down into multiple small pulses of fixed width, but instead concentrates it into a single small pulse. Utilizing the physical property in electron accelerators that "pulse dose and pulse width are linearly related," the required pulse width for this single small pulse is directly deduced and dynamically calculated based on the remaining dose.

[0049] By locking the total number of pulses to "N+1", the beam exit time and frequency are completely locked, thereby achieving precise and balanced control of the radiotherapy dose rate.

[0050] The specific implementation steps of this application are as follows, taking a target dose of 10 Gy, a target dose rate of 250 Gy / s, a large pulse dose A1 = 1.5 Gy, and a pulse width W1 = 3 μs as an example: Step S1: The ray control system acquires the target parameters and calculates the target beam exit time.

[0051] The operator inputs the target dose D1=10Gy and the target dose rate R=250Gy / s. The dose rate refers to the radiation dose per unit time. Based on the target dose and the target dose rate, the radiation control system calculates the target beam exit time T=D1 / R=10 / 250=0.04s.

[0052] Step S2: The X-ray control system calculates the number of fixed large pulses.

[0053] The radiation control system calculates the number of pulses N = D1 / A1 = 10 / 1.5 = 6.67 based on the preset single pulse dose A1 = 1.5 Gy, and rounds down to get N = 6.

[0054] Step S3: The radiation control system calculates the remaining dose that needs to be replenished.

[0055] The large pulse dose is D2=N A1=6 1.5 = 9 Gy; The remaining dose is D3 = D1 - D2 = 10 - 9 = 1 Gy.

[0056] Step S4: The ray control system calculates the variable small pulse width.

[0057] The small pulse dose is A2=D3=1Gy; Based on the linear relationship between pulse dose and pulse width, the radiation control system calculates the variable small pulse width W2=(A2 / A1). W1 = (1 / 1.5) × 3 = 2us, so the final pulse width W2 = 2us is determined.

[0058] Step S5: The X-ray control system determines the beam pulse frequency.

[0059] The total number of pulses emitted in this beam is determined to be M = N + 1 = 7.

[0060] Dose rate = dose / beam egress time. Since the beam egress time is taken as the time from the rising edge of the first pulse to the falling edge of the last pulse, it is one pulse cycle short (the pulse itself is only a few microseconds and can be ignored). Therefore, the number of pulses needs to be subtracted by 1 when calculating the pulse frequency. It should be noted that in other embodiments, the subtraction of 1 is not necessary when calculating the pulse frequency.

[0061] Calculate and lock the output pulse frequency F=(M-1) / T=6 / 0.04=150Hz.

[0062] Step S6: The radiation control system sends out the target dose value information.

[0063] The radiation control system sends the target dose value information to the radiation monitoring system. At the same time, the radiation control system also sends the preset beam exit time to the radiation monitoring system. When the beam exit dose is greater than or equal to the D1 target dose of 10Gy, or when the cumulative beam exit time is greater than or equal to the preset beam exit time, the target beam exit time plus the preset time margin equals the preset beam exit time. Immediately within 500us, an interlocking beam stop signal is sent to the radiation generating system to prevent excessive dose.

[0064] Step S7: Emit beam parameters under the radiation control system.

[0065] The radiation control system sends all beam output parameters to the modulator of the radiation generation system, including 6 large pulses, 1 small pulse, a frequency of 150 Hz, a large pulse width of 3 μs, and a small pulse width of 2 μs. For example... Figure 2 As shown.

[0066] Step S8: The X-ray generating system outputs a beam.

[0067] After the operator completes the "beam exit confirmation" in the X-ray control system, the X-ray control system sends the beam exit command to the X-ray generation system. Upon receiving the beam exit command from the X-ray control system, the channel generator integrated in the central timing board simultaneously generates three independent electrical pulse signals, which are output to the electron gun, klystron, and microwave excitation power source, respectively.

[0068] When the klystron is triggered by an electrical pulse signal, its cathode emits a high-intensity electron beam. Simultaneously, a microwave excitation power source is triggered, generating a low-power but extremely stable small microwave signal, which is injected into the klystron's input cavity. The kinetic energy of the high-energy electron beam is converted into microwave energy, ultimately forming a high-power microwave pulse with a peak power reaching megawatt levels in the klystron's output cavity. This microwave pulse is then transmitted to the accelerating tube via a rectangular waveguide filled with sulfur hexafluoride gas. The greater the microwave energy, the higher the microwave pulse power.

[0069] At the same moment, the electron gun is also triggered. The electron gun power supply generates a negative high-voltage electric pulse, which is applied to the cathode of the electron gun. This pulls the electron beam out from the cathode surface and pre-accelerates it to an initial energy close to half the speed of light, which is then injected into the acceleration tube.

[0070] The electron gun enables precise injection of the electron beam into the accelerating tube, while the klystron enables precise injection of the microwave into the accelerating tube. The electron beam injection into the accelerating tube has strict synchronization requirements with the microwave pulse; it must fall within the plateau period after the microwave pulse has been amplified to a steady state by the klystron to ensure stable acceleration of the electron beam.

[0071] Inside the accelerating tube, the axial alternating electric field established by high-power microwaves keeps the electron cluster at the peak of the accelerating phase. Through the relay effect of multiple accelerating cavities, the electrons continuously gain kinetic energy, eventually reaching megaelectron volts. After acceleration, the electron beam is broadened by the scattering foil at the end of the accelerating tube and then constrained by a 3-10 cm diameter light-limiting tube to form a uniformly distributed electron beam before exiting. This completes one physical beam emission pulse cycle. The channel generator then triggers the pulse signal repeatedly until all large pulses have been emitted, completing the entire large pulse beam emission process.

[0072] When the X-ray generating system detects that N pulses with a width of 3µs have been emitted, the central timing board immediately modifies the pulse width of the electrical pulse signal sent to the electron gun power supply to 2µs. The electron gun power supply shortens the IGBT conduction time, and the high-voltage pulse width of the electron gun narrows accordingly, reducing the charge discharged per electron beam. The klystron output microwave width and power remain unchanged, and the electron beam current still falls within the plateau period after the microwave pulse is amplified to a steady state by the klystron. Subsequently, the small-pulse-width beam emission is completed, thus completing the entire beam emission process of N fixed large pulses + 1 adjustable-width small pulse. The central timing board then stops sending pulse signals to the electron gun, klystron, and microwave power source, achieving beam termination.

[0073] The central timing board of the X-ray generation system is built on a high-performance FPGA and is the core control device of the modulator. It contains a channel generator, a forward and backward counter, and a beam output enable control logic gate circuit. It is responsible for generating and distributing the synchronous clock, trigger signal, and various timing logic control signals required by the entire system, ensuring that each component works in a coordinated manner according to a precise time sequence.

[0074] For each trigger pulse emitted by the X-ray generation system, the forward counter increments the "prompt pulse" value. Simultaneously, a current transformer in the pulse switching circuit detects the actual discharge waveform, and after shaping, an independent backward counter increments the "actual pulse" value. The two count values ​​are verified in real time within each pulse cycle. Only perfectly matched valid pulses are ultimately confirmed as output pulses, thus allowing the X-ray generation system to accurately determine the number of output pulses. The forward and backward counters are integrated into the central timing board.

[0075] A pulse switching circuit is a control circuit that uses a thyristor or IGBT as the core switching device to release the energy stored in the energy storage capacitor in the modulator power supply to the transformer via pulses. The transformer receives the pulsed electrical energy and transfers it to the klystron, which then converts the pulsed electrical energy into pulsed microwave energy.

[0076] During beam exit, in front of the electron exit window at the end of the accelerating tube, the radiation monitoring system has two physically identical but independent ionization chambers. Each ionization chamber is equipped with an independent high-voltage power supply for power supply and signal amplification circuitry. When the radiation passes through the ionization chamber, it ionizes the gas inside, generating a weak ion current, which is proportional to the instantaneous dose rate. The signal from each ionization chamber is amplified by the signal amplification circuit and then sent to an independent integrator to calculate the beam dose value in real time.

[0077] The high-speed comparator inside the ionization chamber continuously compares the output dose value from the ionization chamber integrator with the preset target dose value. This is a hardware-level comparison, independent of the central processing unit's software loop. When any ionization chamber detects that the cumulative dose value is greater than or equal to the set target dose for the first time, its corresponding comparator immediately activates, directly outputting an interlocking beam stop level signal to the emergency stop port of the radiation generation system via a signal line within an extremely short response time of 500 microseconds.

[0078] To completely eliminate the risk of overdose due to ionization chamber malfunctions, the system incorporates independent time-based redundancy protection. The control system adds a hard tolerance threshold, known as a "time margin," to the calculated theoretical beam egress time, for example, 100 to 500 microseconds. This total time limit is loaded into a separate hardware watchdog timer, built into the radiation monitoring system. This timer only accepts the beam egress start signal and begins its countdown. Once the total beam egress time reaches this preset time limit, regardless of whether either ionization chamber has given a dose arrival signal, the time watchdog will forcibly trigger the interlock, directly cutting off the modulator's high-voltage trigger pulse. This means that even if both channels of the radiation monitoring system fail simultaneously and fail to output a beam stop signal when the target dose is reached, the time protection interlock can limit the total beam egress dose to an acceptable range, preventing catastrophic overdose accidents.

[0079] The beam output enable control logic gate is integrated into the central timing board. This is a hardware-priority logic gate. Under normal conditions, the enable pin remains high, allowing trigger pulses to pass. Upon receiving any beam-stop interlock signal, the logic gate immediately pulls the enable pin low without delay, shutting it down. The blocked trigger pulse will not reach the thyristor's drive stage, instantly terminating the high-voltage pulse generation process, and beam output will be rigidly stopped within the same microsecond cycle. Simultaneously, the system latches the interlock source and displays "Dose Interlock Stop" or "Time Interlock Stop" on the human-machine interface, requiring the operator to reset and check before the next beam output attempt.

[0080] Through the closed-loop process described above, which includes "precise synchronization of pulse timing, dose protection of dual ionization chambers, independent redundancy in the time dimension, and emergency beam cutoff of hardware signals," the X-ray generation system constructs a beam output control system that conforms to the "single fault safety principle." It generates X-rays with nanosecond-level synchronization accuracy and ensures dose cutoff with microsecond-level response speed, thereby achieving precise control and absolute safety of the output beam in both physical and execution logic.

[0081] See Figure 3 This application also provides an embodiment of an electronic FLASH radiotherapy beam output control system for implementing the electronic FLASH radiotherapy beam output control method of the above embodiment, including a radiation control system, a radiation generation system and a radiation monitoring system; The radiation control system is used to acquire the target dose and target dose rate, calculate the target beam exit time, and complete the calculation of the number of large pulses, remaining dose, small pulse width, total number of pulses, pulse number threshold, and beam exit pulse frequency. The pulse number threshold is equal to the total number of pulses plus the number margin. It sends the target dose value and preset beam exit time to the radiation monitoring system, and sends the number of large pulses, small pulses, large pulse width, small pulse width, beam exit pulse frequency, and beam exit command to the radiation generating system. The X-ray generation system is used to receive beam emission commands and execute pulsed beam emission, completing the generation, transmission, acceleration and emission of the electron beam, and terminating pulsed beam emission upon receiving a stop signal; The radiation monitoring system is used to receive the target dose value and preset beam exit time issued by the radiation control system, monitor the cumulative dose and cumulative beam exit time in real time, and output a beam stop signal based on the monitoring results.

[0082] Optionally, the radiation control system includes a controller, a human-machine interface, and a storage module; The storage module is used to store preset large pulse doses, corresponding large pulse widths, and linear relationship parameters between pulse dose and pulse width; The controller is used to calculate the target beam egress time based on the target dose and target dose rate, calculate the number of large pulses and the remaining dose based on the preset single large pulse dose, calculate the small pulse width by combining linear relationships, and finally determine the total number of pulses, the pulse number threshold, and the beam egress trigger pulse frequency. The pulse number threshold is equal to the total number of pulses plus the number margin. It sends the target dose value and preset beam egress time to the radiation monitoring system and sends relevant parameters to the radiation generation system. At the same time, it completes the latching of the trigger source. The human-machine interface (HMI) is used to receive operator commands, output shutdown prompts, and support equipment reset checks. Target dose and target dose rate can be input through the HMI.

[0083] Optionally, the radiation generating system includes a modulator, a microwave excitation power source, an electron gun, a klystron, and an accelerator tube; The channel generator is used to receive the beam output command and output three synchronous electrical pulses to trigger the electron gun, klystron, and microwave excitation power source to work respectively. The solid-state modulator is used to release the energy of the energy storage capacitor, which is then used to generate a high-voltage pulse through a transformer to drive the klystron to produce an electron beam. The microwave excitation power source is used to output a reference microwave pulse. The electron beam and the reference microwave pulse are converted into microwave pulses in the klystron and then transmitted to the accelerator tube via a rectangular waveguide. At the same time, the electron gun is triggered, and the electron gun power supply outputs a negative high voltage pulse. This negative high voltage pulse acts on the electron gun cathode to extract the electron beam, and pre-accelerates the electron beam to a preset speed before injecting it into the acceleration tube. The electron beam flows within the stable operating range of the microwave pulse. The accelerating tube is used to keep the electron beam at the peak of the accelerating phase. Through the relay action of multiple accelerating cavities, it continuously acquires kinetic energy and finally forms a high-energy electron beam. The beam exits from the end of the accelerating tube and is successively broadened by the scattering foil and constrained by the light-limiting tube to form a uniformly distributed electron line. The beam is then emitted in a single pulse by the radiation generation system.

[0084] Optionally, the central timing board is part of the modulator. As the controller of the modulator, the central timing board integrates a channel generator, a forward counter, a backward counter, and a beam enable control logic gate circuit. The channel generator is used to receive the beam output command and output three synchronous electrical pulses to trigger the electron gun, klystron, and microwave excitation power source to work respectively. For each trigger pulse emitted by the X-ray generation system, the forward counter increments the corresponding pulse. The pulse switching circuit detects the actual discharge waveform through a current transformer. After the waveform is shaped, the backward counter increments the actual pulse. The two counters verify the count value in real time within each pulse cycle. If the count values ​​match perfectly, the pulse is determined to be a valid pulse. This is used to count the actual number of beams emitted. Only valid pulses participate in the cyclic beam emission until all preset pulses are output. Then, a beam stop signal is output to the beam emission enable control logic gate. Under normal conditions, the enable terminal of the beam output enable control logic gate circuit remains at a high level, allowing trigger pulse transmission. Upon receiving the beam stop signal, it immediately pulls the enable terminal low without delay, blocking the transmission of the trigger pulse to the pulse switch driver stage and terminating the modulator's electrical pulse signal generation process.

[0085] Optionally, the radiation monitoring system includes two independent ionization chambers and a timer, with the watchdog timer isolated from the ionization chamber signal circuit; each ionization chamber is equipped with an independent high-voltage power supply, signal amplification circuit, integrator and comparator, and the high-voltage power supply is used to power the corresponding ionization chamber; Both ionization chambers receive electron beams output from the radiation generation system. The electron beams ionize the gas inside the ionization chambers and generate an ion current, which is proportional to the instantaneous dose rate. The ion current generated in each ionization chamber is first amplified by a signal amplification circuit and then sent to an integrator. The integrator accumulates and calculates the output dose value in real time. The comparator continuously compares the output dose value of the integrator with the target dose value. When the output dose value detected by any ionization chamber is greater than or equal to the target dose value for the first time, the comparator outputs a beam stop signal. A preset time margin is added to the target beam emission time to form a total time limit. After the beam emission time reaches the total time limit, the watchdog timer outputs a beam stop signal to the beam emission enable control logic gate of the X-ray generation system so that the X-ray generation system stops emitting beams.

[0086] This application also provides an embodiment of an electronic device, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the electronic FLASH radiotherapy beam control method of the above embodiment.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and not to limit them. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of this application. Any modifications or equivalent substitutions that do not depart from the spirit and scope of this application should be covered within the protection scope of the claims of this application.

Claims

1. A method for controlling the beam output in electronic FLASH radiotherapy, characterized in that, include: S1. Based on the target dose and target dose rate, obtain the target beam exit time; S2. Based on the preset single large pulse dose, calculate the number of large pulses and the remaining dose; S3. Based on the linear relationship between a single large pulse dose and a large pulse width, and the remaining dose, calculate the small pulse width and the number of small pulses, wherein the number of small pulses is 0 or 1; S4. Determine the total number of pulses based on the number of large pulses and the number of small pulses, and calculate the beam pulse frequency based on the total number of pulses and the target beam emission time; S5. Execute the beam output command based on the number of large pulses, the number of small pulses, the width of large pulses, the width of small pulses, and the output pulse frequency; S6. When any one of the following conditions is met: the cumulative number of pulses equals the pulse number threshold, the cumulative dose is greater than or equal to the target dose, or the cumulative beam emission time is greater than or equal to the preset beam emission time, pulse emission is terminated. The pulse number threshold is equal to the total number of pulses plus the number margin.

2. The method for controlling the output beam of electronic FLASH radiotherapy according to claim 1, characterized in that, S1 includes: The target beam exit time is obtained by dividing the target dose by the target dose rate.

3. The method for controlling the output beam of electronic FLASH radiotherapy according to claim 1, characterized in that, S2 includes: Divide the target dose by the preset single large pulse dose, and round the quotient down to get the number of large pulses; Calculate the total dose of all large pulses based on the number of large pulses and the dose of a single large pulse; The difference between the target dose and the large pulse dose is calculated to obtain the remaining dose.

4. The method for controlling the output beam of electronic FLASH radiotherapy according to claim 1, characterized in that, S3 includes: Based on the linear relationship between pulse dose and pulse width, using a preset single large pulse dose and large pulse width as a benchmark, and combining the remaining dose for proportional conversion, the small pulse width is derived in reverse.

5. The method for controlling the output beam of electronic FLASH radiotherapy according to claim 1, characterized in that, S4 includes: The total number of pulses is obtained by summing the number of large pulses and the number of individual small pulses. The total number of pulses is then divided by the target beam emission time, or by subtracting one from the total number of pulses and dividing by the target beam emission time, to obtain the beam emission pulse frequency.

6. The method for controlling the output beam of electronic FLASH radiotherapy according to claim 1, characterized in that, S6 includes: Monitor the cumulative number of pulses, cumulative beam time, and cumulative dose.

7. The method for controlling the output beam of electronic FLASH radiotherapy according to claim 6, characterized in that, When the cumulative number of pulses equals the number of large pulses, adjust the pulse width to the small pulse width.

8. The method for controlling the output beam of electronic FLASH radiotherapy according to claim 1, characterized in that, The preset beamout time is equal to the target beamout time plus the preset time margin.

9. An electronic FLASH radiotherapy beam output control system, characterized in that, This includes a radiation control system, a radiation generation system, and a radiation monitoring system; The radiation control system is used to acquire the target dose and target dose rate, calculate the target beam emission time, and complete the calculation of the number of large pulses, the number of small pulses, the width of large pulses, the width of small pulses, the total number of pulses, and the beam emission pulse frequency; it sends the target dose and preset beam emission time to the radiation monitoring system, and sends the number of large pulses, the number of small pulses, the width of large pulses, the width of small pulses, the beam emission pulse frequency, and the beam emission command to the radiation generating system. The radiation generating system is used to execute beam output commands based on the number of large pulses, the number of small pulses, the width of small pulses, and the frequency of the output pulses. When any one of the following conditions is met: the cumulative number of pulses equals the pulse number threshold, the cumulative dose is greater than or equal to the target dose, or the cumulative beam emission time is greater than or equal to the preset beam emission time, the radiation generation system terminates pulse emission. The pulse number threshold is equal to the total number of pulses plus the number margin. The radiation monitoring system is used to monitor the cumulative dose and cumulative beam emission time. When any of the following conditions are met, the cumulative dose is greater than or equal to the target beam emission dose and the cumulative time is greater than or equal to the preset beam emission time, the system outputs a beam stop command to the radiation generating system.

10. The electronic FLASH radiotherapy beam output control system according to claim 9, characterized in that, The radiation control system includes a controller and a storage module; The storage module is used to store preset large pulse dose, corresponding large pulse width, and linear relationship parameters between pulse dose and pulse width; The controller is used to calculate the target beam emission time based on the target dose and target dose rate, calculate the number of large pulses and the remaining dose based on the preset single large pulse dose, and then calculate the small pulse width in combination with the linear relationship to determine the total number of pulses and the beam emission trigger pulse frequency. The system sends the target dose and preset beam emission time to the radiation monitoring system, and sends the number of large pulses, the number of small pulses, the width of large pulses, the width of small pulses, the beam emission pulse frequency, and the beam emission command to the radiation generating system.

11. The electronic FLASH radiotherapy beam output control system according to claim 10, characterized in that, When the cumulative number of pulses equals the number of large pulses, the radiation generating system adjusts the pulse width to a small pulse width.

12. The electronic FLASH radiotherapy beam output control system according to claim 9, characterized in that, The preset beamout time is equal to the target beamout time plus the preset time margin.

13. An electronic device, characterized in that, The method includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, it implements the electronic FLASH radiotherapy beam control method according to any one of claims 1-8.

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