摘要Objective:The aim of this work was to quantify the extent of set-up errors to conduct a quality assurance (QA) aspect of treatment delivery, verification of the treatment field's position on dif erent days using electronic portal. Methods:This study was carried out on 12 patients, treated for pelvis tumor;and total of 240 images obtained by electronic portal image device (EPID) were analyzed. The EPIs acquire using EPID attached to the Siemens linear accelerator. The anatomy match-ing software (Theraview) was used and displacement in two dimensions were noted for each treatment field to study patient setup errors. Results:The percentages of mean deviations less than 5 mm in X direction were 65%&92%, from 5–10 mm were 31%&19%and more than 10 mm were 11%&9%for A/P and lateral direction respectively. The percentages of mean deviations less than 5 mm in Y direction were 65%&63%, from 5–10 mm were 33%&28%and more than 10 mm were 22%&29%. The mean deviations in 2D-vector errors were≤5 mm in 47%and 46%, 5–10 mm in 36%and 37%and>10 mm in 37%and 37%of images in the A/P and lateral direction respectively. Conclusion:The results revealed that the ranges of set up errors are immobilization method to improve reproducibility. The observed variations were not within the limits..