Research On Several Key Techniques Of Intensity Modulated Radiation Therapy System

Intensity Modulated Radiation Therapy (IMRT) is a perfect radiation therapy techniqueand has become the mainstream of the development of radiation therapy. It can increase theradiation dose ratio of target to healthy tissue. In other words, it can deliver a homogenousradiation dose to a planned target volume while sparing or avoiding healthy tissuesurrounding. Now, the research on IMRT is still on the academic phase, facing with manyunfathomed key techniques. Moreover the research on IMRT has not been carried out inChina. In this paper, the relevant theory and key techniques are lucubrated, aiming atimproving the radiation dose ratio of target to healthy tissue, including medical imageprocessing, three-dimension reconstruction, three dimension model processing, dosecalculation and treatment plan optimization, the equipments and methods of IMRT, and soon. Firstly, the issue of medical image processing aiming at IMRT is studied in this paper.An algorithm based on edge mould for the automatic extraction of the body contours isproposed, after analysis and comparison of existing image processing techniques. Based onthis algorithm, medical images can be segmented semi-automatically. For the three-dimension reconstruction of medical images, a fast triangulation algorithmfrom planar contours (FTA) is proposed in this paper. In FTA, the judgment of similarity ofcounters is carried out at first. Then the simulated annealing algorithm (SA) is applied todissimilar contours' triangulating. And a relative simple local optimization method isapplied to similar contours' triangulating. The visual effect of FTA is parallel with that oftraditional global optimization methods and at the same time its calculating speed has beenimproved much. Aiming at the practical implementation of IMRT, the visualization and processingmethods for three-dimension models are studied. Based on the construction of surfacemodel which has explicit adjoining and indexing relationship among triangle patches, a fastalgorithm to slice the triangulation model by arbitrary sections is proposed. The dose calculation model is also discussed in this paper. On base of the treatment planoptimization model which aims at the dose uniformity and dose grads between target andhealthy tissue, the genetic algorithm (GA) is applied to IMRT plan optimization and itsprocedure is also introduced.On account of the wide use of multi-leaf collimator (MLC), the implementation ofdensity modulation using MLC is probed into, including static density modulation, dynamicdensity modulation and scanning density modulation. The leaves moving model and controlstrategy is put forward. And the matter about the acceleration limit of leaves is alsodiscussed. According to the peculiarity of the focus therapy machine, a focus scanning method fordensity modulating is put forward for the first time, and its concept, theory andimplementing methods are researched primarily. Finally, the theory and methods introduced above will be applied to the developedequipment and the treatment planning system for IMRT, namely "OUR-QGD ModelStereotactic Gamma Ray Whole-body Therapeutic System (the Whole-body GammaKnife)"and "XG-TPS". Then the academic research is combined with practicalimplementation.