Research On Optimization Algorithm In Inverse IMRT Planning

As an advanced technique of three-dimentional conformal radiotherapy, IMRT has been applied into clinical oncology world widely. Not only can IMRT conform to the target in three-dimentional direction, but also produce highly three-dimentional conformal dose distribution to the target. IMRT has significant potential for improving the therapeutic ration and reducing toxicity.IMRT treatment plans are often generated using inverse planning, which is different from traditional forward planning. First, doctor determines the prescribe dose. Then optimization techniques are used to help determine the distribution of intensities across the target volume.This paper is focused on the research of the optimization for the inverse planning of IMRT. Firstly, the dose calculation models of both regular fields and irregular fields have been presented, where the dose calculation method based on the pencil beam model is mainly introduced. Secondly, the optimization method has been studied for IMRT inverse planning. The simulated annealing algorithm and simplex method are combined to generate SMSA algorithm, which is used to optimize the aperture shape and weight. In order to protect the normal tissue around the target and reduce the calculation, we set up a new model. The objective function is based on dose constrain as well as the dose homogeneous constrain and important factors of tissue. Finally, two and three dimensional isodose contour and dose-volume histogram are used to evaluate the treatment plan.The results show that the SMSA algorithm can yield low doses to sensitive tissues without resulting in substantial nonuniformities in the high dose to the treatment volumes. The SMSA algorithm and objective function we put forward has great significance and application value in clinic.