Research On Several Key Techniques Of Clinic Of Multi-leaf Collimator Radiation Therapy System

The project is aided financially by Wu Jieping Medical Foundation for Clinical Research. Intensity Modulated Radiation Therapy (IMRT) and the quality control of multi leaf collimator (MLC) are chiefly reaserched in this thesis. Based on that, some key techniques on clinical application of IMRT are lucubrated, the radiotherapy system is further perfected, and the matter about imperfect motor drive of MLC in clinical application is improved. The chief goal of this project is to perfect IMRT system and to solve the questions of clinical applications. The main contents are as follows.The problem about segmentation of medical images is the base of three-dimension reconstruction during IMRT, since the irradiation precision during radiotherapy is directly affected by the quality of image segmentation. In this dissertation, the research on medical image segmentation is carried out main aiming at automatic image segmentation, a MRF (Markov Random Field) model about self-reacting energy function is proposed, during the energy function is minimizated, the weighting factors of the energy function in the conditional probability model are dynamically adjusted, and the global optimization parameters about the observation field are obtained. Based on that, the segmented results of tumor images are filtered with morphology operator, some holes and isolated noise elements are eliminated by opening and closing operations. Finally, on the base of the segmented results of tumor images, Canny edge extraction operator is used to margin the regions and extract the closed edge.Three-dimension reconstruction of medical images is the key of radiation therapy system, and construction of volume data is the prerequisite of three-dimension reconstruction. In this dissertation, a method based on vector distance transformation is proposed to calculate the symbol distance function. By this method, which firstly define a symbol distance function and then put forward the construction method of the symbol function, the speed and efficiency of calculating symbol distance field are raised greatly. This method is not only precise and highly robust, but promotes the construction of volume data field. Marching cubes (MC) and marching tetrahedral (MT) algorithm are used to complete the three-dimension reconstruction of volume data and realize visualization based on the construction of volume data field. In the project, MT algorithm is probed into, and the practical application matter of MC algorithm is solved.The dose models of regular and irregula fields are analyzed and summarized in this thesis. A few traditional dose algorithms such as Monte Carlo method and Clarkson's scatter summation method are introduced, Day's function method is studied, by which the equivalent square field is obtained through sector integration to the standard scatter dose data and the dose distribution in irregular field is exactly calculated.The realizing ways of intensity modulation by MLC which is an important executive part of IMRT are discussed. Aiming at static intensity modulation techniques by MLC, the grade scale of dose distribution is also discussed, the methods and train of thoughts which are used to define the shapes of different irradiation fields are proposed; For dynamic leaf intensity modulation by MLC, the intensity modulation theory is studied, leaves moving model and strategy are put forward, leaves moving regular and the matter about the acceleration limit of leaves are discussed. Aiming at the weakness that the DC servo motors and step motors of MLC often have a breakdown, the brushless DC motors which have no carborn brush are proposed as control parts of MLC. By clinical experiment, the practical application questions of MLC in clinic are solved.Finally, the emulation experiments for the key techniques such as image segmentation and 3D reconstruction are carried out, the efficiency of brushless DC motors used as the control parts of MLC is put to the proof by clinical application, and the reaserches are verified to be effective and practicable.