Research On Dose Calculation Model For Three-Dimensional Conformal Radiotherapy

Radiotherapy is one of the most important methods for tumor treatment and engages computer radiotherapy treatment planning system as its key tool. In this thesis, we focused on one of the key problems: dose calculation, which is crucial to develop a three-dimensional radiotherapy treatment planning system.The precision attained and the time spent in computing dose is crucial to the practicability of a radiotherapy treatment planning system. According to the shape of irradiation field, we advance two kinds of dose calculation models separately for high-energy X-ray regular and irregular field, thus achieving the compromise precision and speed.The dose calculation model used for regular irradiation field is a corrected model using measured dose data. Using this model, dose computing result of regular field can be obtained immediately. Through reforming original dose calculation models established for regular irradiation field, we present a set of more efficient and systematical solution to calculate dose distribution of regular irradiation field. The detailed topics include: dose calculation models on opening symmetric rectangle field, wedge field and asymmetric rectangle field; revised numerical processing methods for depth dose and off axis ratio. Because of easy method and ample data sources, this dose calculation model is feasible for its more accurate precision and almost real-time speed when used for computing three-dimensional dose distribution with the regular irradiation fields.The dose calculation model advanced for irregular irradiation field bases on two-dimensional convolution principle. This model can be applied to calculate three-dimensional dose distribution for irregular irradiation field configured for conformal radiation therapy. In this part, our research results are as follows: a pencilbeam model established on the basis of extraction pencil beam kernel by the deconvolution method; a penumbra calculating model and its fast algorithm; convolution kernels reconstruction methods based on pencil beam; the irregular field forming method. We have done a lot of experiments, and the results have shown that this dose calculation model can achieve satisfactory precision and fast speed. As a result, it is a general method to dose calculation.At the end of this thesis, we also discuss some problems which haven't been completed. In addition, we prospect some work which we'll do in the future.