Abstract: Mechanical Errors of equipments which shows a gradual increasing trend along with the increase of running time is one of the important sources that compromise the spatial accuracy of radiation dose delivery. Therefore research on the deformation of radiation field caused by mechanical errors and corresponding solutions is of great significance in clinic treatment. Mathematical modeling of the x-ray delivery process is introduced at the beginning of this article, where the laws of field deformation along with mechanical errors of each freedom are achieved. Afterwards a finite-point dimensional search method is proposed to measure the deformation of the radio field. Then, a compensation algorithm based on multi-leaf collimator is put forward by region segmentation of radiation field, calculation of best approximation radiation field and inverse of vertex coordinates of multi-leaf collimator. At last, numerical simulation of the compensation algorithm is conducted by using four actual radiation fields. The result of the simulation shows that the compensation algorithm can reduce the radiation field shape deformation by about 50%, which improves accuracy of radiation therapy significantly.

Key words: compensation, mechanical error, multi-leaf collimator, precise radiotherapy, radiation field