Reliability Analysis Of Multi-leaf Collimator In Medical Linear Accelerator Based On Simulation

Medical linear accelerators are equipment used for radiation therapy of tumors.Multi-leaf collimator is an important component of medical linear accelerators,consisting of a blade box assembly,a box drive assembly,and a drive plate assembly.Each blade has a separate drive,and the shape of the irradiation field corresponding to the tumor focus is formed by changing the position of the blade.The high utilization rate and complex structure of multi leaf collimator blades lead to a high failure rate of multi leaf collimators.To ensure the quality of tumor radiotherapy and the safety of patients,it is vital to improve the reliability of the multi-leaf collimator.Due to the high price of multi-leaf collimators,the experiment on physical models will take a long time and cost a fortune.Using simulation analysis methods to replace physical model experiment can greatly reduce the time and cost of research and development.In the thesis,a simulation-based method is proposed to carry out the reliability analysis of multi-leaf collimators,which can provide theoretical support for improving their structural design and reliability indicators.It is of great significance for improving the reliability of domestic medical linear accelerators and reducing their costs.The research work of the thesis includes the following aspects:(1)Firstly,the FMECA and FTA of multi-leaf collimator are carried out.Based on study of the working principle of the multi-leaf collimator system,the structure and composition of the multi-leaf collimator are analyzed,and the structural and functional logic diagram is drawn.All possible failure modes and effects of the multi-leaf collimator are obtained,and then fault trees are established using the events with high hazard and frequency as the top events.After qualitative analysis,the bottom events are divided into mechanical failures and electronic failures.The outcomes of FMECA and FTA lay the foundation for subsequent reliability simulation.(2)Based on the finite element method,the simulation analysis of mechanical faults in the multi leaf collimator is accomplished.The reliability simulation analysis of the multi leaf collimator are employed to analyze the effects of torque,screw diameter,elastic modulus of screw material,and density of blade material on the deformation of the screw.Using first order reliability analysis,25 sets of design points are selected for response surface calculation,and the probability distribution of the deformation of the screw is obtained.(3)The circuit system reliability simulation using Saber is accomplished.The drive board circuit of multi-leaf collimator is taken as an example;the fault injection and system modeling are studied for the offset fault in the circuit tolerance fault.Bootstrap method is used to evaluate the life of small samples of electronic components under radiation environment.Saber is a software,which can used to accomplish the quantitative analysis of fault modes and functional fault simulation analysis of circuits to obtain the functional reliability of circuits.(4)Combined with Monte Carlo and fault tree analysis,the reliability simulation analysis of "the multi-leaf collimator blade can work normally" is carried out.Based on the analysis conclusions in the previous chapters,a simulation program is carried out to obtain the simulation value of mean time between failures,and compare it with the theoretical calculation value to prove the accuracy of the simulation.At the same time,the dynamic reliability curve,failure probability density curve,and bottom event importance simulation results are obtained through simulation.