模拟定位机图像的数字化及图像畸变校正

Correction of distorted digital images generated by radiotherapy simulator

目的测量模拟定位机数字化图像的畸变程度，并寻找合适的算法来校正图像的畸变，以保证放疗的精度。方法自制网格校正板，利用Microsoft Visual C＋＋6．0编程工具编制校正算法，计算图像校准前后的面积误差和边界最大位移误差，并将校准后图像与胶片图像进行比较，以评估校准方法的可靠性。结果校正前，相对于4em×4cm-12cm×12cm范围照射野，会使设计的照射野与实际执行的照射野产生0．31％～12．36％的面积误差，并且会导致射野边缘与设计时产生0～6mm以上的位移偏差。校正后，在常用照射野范围内（12cm×12cm），图像畸变造成的面积误差和边界最大位移分别为0．48％和0．46mm。结论模拟定位机数字化畸变图像经过最小二乘法拟合多项式的方法进行校正后可满足临床常规放疗的精度要求。

Objective To measure the distortion of digital images generated by radiotherapy simulator,and to study the appropriate method of correction. Methods The grid correction plate and Microsoft Visual C ＋ ＋ 6.0 were used for correction. The area error and boundary maximum displacement error of digital images before and after correction were calculated. The post-correction images were compared with film images to evaluate the correction method. Results The area error was 0.31% - 12.36%, and the boundary displacement error was more than 0 - 6 mm for 4 cm× 4 cm - 12 cm × 12 cm radiation field before correction. For commonly used radiation field （ 12 cm × 12 cm）, the post-correction area error and the boundary displacement error were 0.48% and 0.46 mm,respectively. Conclusions The least square and polynomial fitting correction method can fulfill the requirement of conventional radiotherapy.