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.
Keywords: Electronic portal imaging; pelvic radiotherapy; port film
