机械误差对肿瘤精确旋转放疗射野变形的影响及补偿算法研究

Research on Radiation Field Deformation and Compensation Algorithm Based on Mechanical Errors during Precise Radiotherapy

放疗设备的机械误差是影响肿瘤放射治疗精确性的重要因素,且随设备使用时间呈现逐渐增大趋势,因此研究机械误差对治疗效果的影响和相应解决方法具有重要意义。首先对旋转放疗设备射线投递的过程进行数学建模,得到治疗头各自由度机械误差对等中心面射野形状的影响规律,并提出了一种用于衡量射野变形的有限点二维搜索方法;然后,通过进行射野区域分割、最佳逼近射野计算以及多叶光栅顶点坐标反算,提出了一种基于多叶光栅的射野变形补偿算法;最后,对四个临床上的实际射野进行了算法的数值仿真试验。结果表明,算法可以有效减少50%左右由机械误差引起的射野形状误差,显著提高了放射治疗精度。

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.