Medical linear accelerators are the core equipment for tumor radiotherapy.

Medical linear accelerators are the core equipment for tumor radiotherapy. They deliver precise irradiation to tumor target areas by generating high‑energy X‑rays or electron beams, serving as the fundamental platform for advanced clinical techniques such as conventional tumor radiotherapy, stereotactic radiosurgery, and image‑guided radiotherapy. The high‑voltage pulsed power supply is an essential power component of medical linear accelerators. It provides high‑amplitude, high‑stability high‑voltage pulses to the magnetron or klystron, driving the microwave system to produce high‑power microwaves that accelerate electron beams and form high‑energy radiation. The amplitude stability, waveform quality, and repetition frequency accuracy of the output pulses directly determine the electron beam energy stability, radiotherapy dose control precision, and overall clinical treatment outcomes. Current mainstream medical linear accelerators require high‑voltage pulsed power supplies with an output amplitude ranging from 20 kV to 50 kV, a pulse width of 2 μs to 10 μs, a repetition frequency of 50 Hz to 1,000 Hz, pulse droop below 1%, and pulse amplitude stability better than ±0.5%. Failure to meet these criteria will cause electron beam energy deviations exceeding 2%, misalign radiotherapy doses from the tumor target, damage surrounding healthy tissue, and even result in severe medical accidents. Traditional hydrogen thyratron modulators and rigid switch modulators suffer from critical drawbacks such as short switch lifespans, low repetition frequencies, severe pulse waveform distortion, and poor long‑term stability, making them incapable of satisfying the stringent dose control requirements of modern precision radiotherapy and stereotactic radiosurgery. Relevant designs must strictly comply with IEC 60601‑2‑1, the dedicated safety standard for linear accelerators in radiotherapy, and GB 9706.21, Part 2‑1 of the medical electrical equipment safety standards covering essential safety and performance for radiotherapy devices. They must also conform to the technical specifications for Class III medical device registration issued by the NMPA. Addressing the core clinical demands and technical challenges of high‑voltage pulsed power supplies for medical linear accelerators, this methodology establishes a comprehensive technical framework covering topological design, solid‑state modulation, dose accuracy control, waveform optimization, and safety compliance. It accommodates the high‑voltage power demands of various medical linear accelerators and provides standardized design principles to support domestic substitution and grassroots promotion of China’s tumor radiotherapy equipment. Focusing on the key challenges of narrow pulses, ultra‑high stability, and precise dose control, this methodology adopts an all‑solid‑state Marx generator as the main topology, utilizing wide‑bandgap SiC MOSFETs as primary power switches within a multi‑stage modular series structure. Each module contains independent energy‑storage capacitors, power switches, and freewheeling diodes. Synchronous triggering of switches enables continuous adjustment of pulse amplitude. Compared with conventional Pulse Forming Network (PFN) topologies, the all‑solid‑state Marx structure eliminates high‑voltage pulse transformers, completely resolving pulse leading‑edge distortion caused by transformer leakage inductance while achieving nanosecond‑level edge control and flexible parameter tuning ideal for narrow‑pulse, wide‑range operation in medical accelerators. The design follows five core principles: First, power device selection prioritizes switching speed, low losses, and long‑term reliability. Automotive‑grade or industrial‑grade 1200 V/1700 V SiC MOSFETs are preferred. Compared with silicon IGBTs, they deliver over ten times faster switching, reduce switching losses by more than 70%, and maintain excellent high‑temperature performance and reliability, significantly extending modulator lifespan and improving pulse waveform quality. Second, fully symmetrical modular circuitry ensures uniform electrical parameters, switching characteristics, and discharge impedance across all stages, preventing asynchronous switching, overvoltage damage, and waveform distortion. Modularity allows flexible amplitude adjustment by changing series stages and current expansion through parallel modules, accommodating accelerators of different energy and power ratings. Third, isolated constant‑current charging with multi‑winding transformers provides independent precise charging for each energy‑storage capacitor, ensuring identical charging voltages under varying repetition frequencies and duty cycles. High‑precision closed‑loop voltage control compensates for temperature drift and component aging, maintaining consistent pulse amplitude stability. Fourth, low‑impedance laminated busbars restrict overall discharge loop parasitic inductance below 3 nH, minimizing leading‑edge degradation, voltage spikes, and ringing while maintaining steep pulse edges free of overshoot and tail distortion. Fifth, fully fiber‑isolated drive circuits provide complete galvanic separation with insulation far exceeding maximum output voltage, eliminating high‑low voltage crosstalk and ensuring switching synchronization accuracy within 10 ns. Precise optimization of solid‑state modulation is central to this methodology. Focused on rigorous pulse waveform requirements, performance enhancement covers synchronous drive control, active pulse droop compensation, and distortion suppression. Nanosecond‑level synchronous drive utilizes an FPGA‑based fully digital control platform with a high‑stability oscillator above 100 MHz, achieving timing accuracy better than 5 ns for perfectly synchronized switching across all stages. Gate drive parameters are optimized with adjustable resistors and active clamping to suppress voltage spikes and electromagnetic interference, protecting beam control and dose monitoring systems. Active pulse droop compensation employs high‑speed ADC sampling above 2 GHz to continuously monitor flat‑top voltage decay. Real‑time FPGA algorithms dynamically adjust switching timing or inject supplementary current during pulse duration, limiting droop within 0.5%—far superior to the standard ±1% requirement. This maintains stable magnetron input voltage, consistent microwave output power, and uniform electron beam energy. Waveform distortion suppression includes impedance matching networks at the high‑voltage output to eliminate transmission‑line reflections, reverse voltage suppression circuits to absorb residual energy and eliminate pulse tail spikes, and optimized grounding plus full shielding to reduce electromagnetic interference and sampling errors. Dose accuracy control ensures compliance with clinical precision radiotherapy requirements through full digital closed‑loop pulse regulation, dose interlock protection, and long‑term stability compensation. High‑resolution 24‑bit ADCs and FPGA enable per‑pulse calibration of amplitude, width, and repetition frequency, achieving long‑term amplitude stability better than ±0.2%, pulse width precision within ±10 ns, and frequency accuracy exceeding ±1 ppm. Multi‑parameter programmable control supports flexible adjustment for conventional radiotherapy, intensity‑modulated radiotherapy, and stereotactic treatment modes. Real‑time interlock integration with ionization chamber dose monitoring dynamically adjusts pulse parameters during irradiation, keeping actual delivered dose within ±1% of planned values. Redundant safety interlocks cut off pulse output within 100 ns if dose exceeds thresholds by 2%, preventing hazardous overexposure. Long‑term stability compensation employs temperature drift algorithms to correct parameter deviations caused by thermal variations and aging compensation to maintain consistent dose output throughout the equipment lifespan, keeping cumulative dose deviation within ±1% for over ten years of continuous operation. Medical safety compliance and reliability form critical constraints for Class III radiotherapy devices. The framework covers electrical safety, environmental adaptability, redundant protection, and full‑lifecycle reliability. Electrical safety adheres strictly to the IEC 60601 series with reinforced double insulation. Isolation withstand voltage exceeds twice the maximum output voltage, while patient and equipment leakage currents remain far below regulatory limits. Fully sealed high‑voltage assemblies eliminate operator exposure risks. Electromagnetic compatibility fully meets GB/T 18268.1 through multi‑layer shielding, multi‑stage EMI filtering, and soft switching, ensuring stable operation in complex hospital environments without interfering with other medical devices. Twelve redundant protection mechanisms include input over/under voltage, output overvoltage, overcurrent/short circuit, overtemperature, arcing, magnetron fault protection, filament failure, dose deviation interlock, door interlock, emergency stop, key switch interlock, and treatment system interlock. All protections feature dual hardware‑software redundancy with fault response below 500 ns for instant high‑voltage shutdown under any abnormal condition. All critical components adopt medical‑grade derating standards with voltage stress ≤70%, current stress ≤60%, and temperature stress ≤80% of rated values to minimize failure risks. Accelerated lifespan testing, thermal cycling, and long‑term aging validation ensure an MTBF exceeding 20,000 hours—double the typical industry standard—supporting continuous clinical operation. In summary, this integrated methodology covers topological design, solid‑state modulation optimization, dose precision control, and full safety compliance. It fundamentally resolves traditional limitations regarding short modulator lifespan, poor pulse stability, and insufficient dose accuracy. Through the all‑solid‑state Marx topology and SiC technology, nanosecond pulse edge control and droop below 0.5% are realized. Fully digital closed‑loop control delivers ±0.2% amplitude stability and radiotherapy dose accuracy within ±1%, while comprehensive safety design satisfies Class III medical device regulations. The solution is widely applicable to medical linear accelerators, providing core technical support for domestic independent innovation, import substitution, and widespread deployment of advanced tumor radiotherapy equipment across healthcare institutions.

Methodology for Solid‑State Modulation and Dose Accuracy Control of High‑Voltage Pulsed Power Supplies for Medical Linear Accelerators