Multi-motor Synchronous Control Strategy And Its Applications In Multi-leaf Control For Multi-leaf Collimator

In the implementation process of radiation therapy,the purpose of using multi-leaf collimator is to replace the traditional manually operated lead block,So that the projection profile of the rays passing through the end of the leaf of the multi-leaf collimator in the target area of the lesion conforms to the profile of the desired shape of the field.In order to meet the needs of conformal radiotherapy,it is necessary to accurately control the accuracy of the leaf of the multi-leaf collimator in place.In view of this problem,and taking into account the multi-leaf synchronous control of multi-leaf collimator,the leaf position control strategy of multi-leaf collimator is studied in this thesis.The main research contents are as follows:1)The basic structure of a multi-leaf collimator in radiotherapy terminal equipment was described,and the composition and mechanism of a multi-leaf collimator control system was analyzed.The motion model and control strategy of the leaves of multi-leaf collimator in static intensity-modulated radiation therapy and dynamic intensity-modulated radiation therapy were established respectively.On this basis,the control requirements of multi-leaf collimator are proposed.2)Each leaf of multi-leaf collimator has a set of independent driving device.In order to ensure the precision of the position of each leaf,the thesis studies the position control strategy of single-leaf of multi-leaf collimator is studied in this thesis.First,the drive unit of the leaf of multi-leaf collimator is selected as the controlled object,and a mathematical model is established.Taking control of the drive unit of the leaf as the primary issue of leaf position control,a single-leaf position PID controller of multileaf collimator is designed according to the mathematical model of the drive unit to meet the requirements of leaf in place accuracy.In order to solve the difficulty of parameter tuning of the position controller,fuzzy controller and Particle Swarm Optimization(including basic particle swarm optimization,Weighted particle swarm optimization and compression factor particle swarm optimization)are adopted respectively to optimize the parameters of the leaf position controller of the multi-leaf collimator,to meet the requirements of the leaves in place accuracy.3)In order to avoid the interference caused by the friction and collision between the leaves because of the mechanical structure of multi-leaf collimator,and to enhance the anti-interference ability of the leaf position controller,improve the precision of the leaf in place,taking into account the problem of PID controller will cause windup phenomenon and the use of particle swarm optimization algorithm is easy to fall into the local optimal solution.In this thesis,a single-leaf position controller of multi-leaf collimator is designed by using fractional order theory and anti-windup controller.The parameters of fractional order anti-windup controller proposed in this thesis are optimized by quantum-behaved particle swarm optimization algorithm,to achieve the purpose of the leaves in place accuracy.4)Multi-leaf collimator is mainly composed by a plurality of leaves,which are arranged in pairs.On the basis of ensuring the control precision of the independent position of each leaf,the synchronization error between the leaves of multi-leaf collimator needs to be considered in order to achieve the purpose of Intensity-modulated Radiocomposition Treatment(IMRT).In this thesis,the concept of multi-leaf synchronization position error is proposed by using cross-coupling control method and three different control strategies have been defined.In view of the characteristics of static intensity-modulated radiation therapy,the multi-leaf PD synchronization control strategy is studied based on cross-coupled control,and the convergence of the synchronization control strategy is proved.The experimental results show that the control strategy proposed in this thesis can reduce the synchronization position error between multi-blades,improves the conformability of the leaves.5)For the dynamic intensity-modulated radiation therapy,the motion of the leaf of multi-leaf collimator is a kind of repetitive motion in the time domain.The iterative learning synchronization conformal control strategy based on cross-coupled for multi-leaf collimator is proposed,on the basis of the multi-leaf PD tracking synchronization control based on cross-coupled.Subsequently,the accumulative position error of adjacent leaves is analyzed,which is caused by the multi-leaf synchronization control strategy,the concept of "virtual main leaf" is proposed to reduce the accumulated position error.Finally,in order to improve the control accuracy of multi-leaf position,a master-slave cross-coupled iterative learning conformal control strategy based on position domain is proposed to meet the requirements of radiation therapy.