Effect Of Different Image Matching Methods On The Position Correction For Nasopharyngeal Carcinoma Patients Underwent Image Guided Radiation Therapy

Objective : To investigate the effects of different image matching methods on the position correction for nasopharyngeal carcinoma patients underwent image guided radiation therapy (IGRT). An algorithm of registration image matching based on unique points was proposed to provide valuable clinical data for daily work and compensate the insufficient of VARIS.Methods:47 pairs of digitally reconstructed radiograph(DRR)images generated by the treatment planning system and port images taken by electronic portal imaging device (EPID) during the course of set up, which come from 37 nasopharyngeal carcinoma patients underwent IGRT, were analyzed by four different image matching methods. Method A, the DRR and EPID images were matched at window width and level automatically chosen by the system, which were based on image gray-scale. Method B, the midpoint of anterior border of first cervical vertebra on DRR and EPID images were matched at automatical window width and level. Method C and D are similar with method A and B, respectively. But manual adjustment of window width and level is allowed. The setup errors of different matching methods on X, Y axes were compared with each other by t test with SPSS13.0 software.On the other hand, the very same 47 pairs of images were matched by the software developed with MATLAB tools. The registration method based on feature points which aims to compensate the insufficient of VARIS was called method E.All the results of differences on X/Y axis werr recorded and put into the same t test with the according data of method A to see if there were any differences.Results:The setup errors on X,Y axes are significantly different for method A vs. B or B vs. D (P<0.05). But no significant difference for method A vs. C,C vs. D or A vs.E (P>0.05). ConclusionsThe setup errors based on image gray-scale and midpoint of anterior border of first cervical vertebra for nasopharyngeal carcinoma patients underwent IGRT are obviously different. But the software of image matching based on feature points algorithm is stable and has no difference from VARIS.