RESUMO
Objective To measure and analyze the set-up errors of postoperative intensity modulated radiation therapy of rectal cancer (PIMRTRC)with electronic portal imaging device (EPID),and to provide theoretical foundation for clinical realizing of accurate PIMRTRC.Methods Totally 30 patients after rectal carcinoma resection underwent sagittal and coronal photographing with EPID before the first time of therapy and one time per week during the treatment course.The obtained images were compared with DRR images in treatment planning system to get the setup errors at X(left-right),Y(head-foot) and Z (front-back)directions,and the extending margins of CTV and PTV in postoperative intensity modulated radiation therapy were calculated.EPID was used for setup correction,and SPSS 19.0 was involved in to execute statistical analysis. Results The linear displacement had the mean values plus/minus standard deviation at X, Y and Z directions before and after error correction being(-1.392 4±3.670 9)mm vs(-0.816 5±2.670 5)mm,(0.969 7±4.076 1)mm vs(0.418 2±2.911 4)mm, and(0.704 4±1.805 6)mm vs(0.471 7±1.641 3)mm respectively;the extending margin had the values being 7 mm vs 5 mm, 6 mm vs 4 mm, and 4 mm vs 3 mm respectively.Conclusion EPID ensures the correctness and accuracy in postoperative intensity modulated radiotherapy of rectal cancer,which makes target area gifted with maximized dose,the surrounding tissue and organs at risk protected adequately,and provides theoretical support for extending CTV margin.[Chinese Medical Equip-ment Journal,2018,39(5):59-63]