Design Of Fast Scanning Magnet System In Proton Therapy Nozzle

The fast scanning magnet system of proton therapy nozzle is important for ensuring that the proton therapy facility delivers the dose to the patient accurately and safely.According to the main performance requirements of the proton therapy facility,the influence of the beam optics in the nozzle on the magnet design is considered.The scanning magnets and switch status of scanning power supply in the fast scanning system are studied and designed,and a power supply control test platform is built with the existing equipments in the laboratory.Based on the theory of dipole iron design,the preliminary analysis of the proton therapy nozzle beam is performed based on Monte Carlo method,and the preliminary design of the two-axis independent scanning magnet and coil related parameters is presented.In order to reduce the number of coil amps,H-type magnets with constant gap and tapered gap are designed.And the electromagnetic simulation software OPERA-3D is used to optimize the structure,so that the lateral integration field uniformity is less than ±0.25%.Modelling the gradient magnetic field along the beam direction is carried out in the way of lamination stacking,and then the optimized magnetic field distribution of the scanning magnet is imported into the Monte Carlo simulation software to analyze the beam spot size and deflection trajectory of the proton beam,and it is verified that when the proton beam is deflected by 150 mm in iso-center plane,the designed good field of the scanning magnet can contain 99.6% of the particles and almost no particles hit the magnetic pole.Finally,the transient analysis of the scanning magnet is carried out.The simulation results show that the magnetic field of the magnet gap can change well with the coil current and meet the design requirements.The scanning magnet is directly controlled by the scanning power supply,requiring a fast-response and high-accuracy power supply.Considering the spot-scanning current waveform and the scanning magnet parameters,the main parameters of the scanning power supply are designed,and the relationship between the voltage and the load current at both ends of the load is analyzed.The control basis of the load current is obtained.The topology scheme and control algorithm of the scanning power supply are performed.The circuit simulation tool Simulink is used to simulate and design the switching state of the power supply.The simulation results show that the load current rise time between spot and spot(steady state 10% rise to 90% steady state)can be controlled within 100 microseconds,and the current can be stabilized at the target value and meet the accuracy of 100 ppm in 200 microseconds.Finally,based on a small power current source in the laboratory,a current source control test platform based on analog signal input is built and a preliminary current source control experiment is carried out.