Comparison of electronic portal image and port film in pelvic irradiation

OBJECTIVES: In this study electronic portal images (EPIs) and port films were compared to detect set up errors and adequacy of image quality. METHODS: In total 40 EPIs and 40 portal films from 20 patients receiving pelvic radiotherapy were evaluated. Image quality was graded by visibility of the selected anatomic landmarks and set-up deviations were examined in the x, y and z axes of the coordinate system. EPIs and port films were compared in terms of Image quality and shifts. RESULTS: Visibility was significantly better for port films than EPIs. In both imaging techniques acetabulum, pelvic rims and symphisis pubis were more visible landmarks. Mean set-up displacements at the x, y and z axes were 1.47, 2.51 and 3.99 mm for port films; 2.16, 3.09 and 3.81 mm for EPIs respectively. Set-up errors were in acceptable levels in all directions, maximum errors were seen in z axis for both images. CONCLUSION: Electronic portal imaging is used widely and takes places of port films. The use of EPI could provide more quick and practical evaluation of set-up errors than port films and also pretreatment correction of set-up errors and digital storage of the images are possible.However the major disadvantage of EPIs than port films is insufficient evaluation of the anatomical structures due to worse image quality.