Tehran University of Medical Sciences Frontiers in Biomedical Technologies 2345-5837 2 3 2015 09 30 155 162 EN Keyvan Jabbari Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran. Nima Rostampour Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran. 2015 12 27 2015 12 27 Purpose- The setup verification is one of the important issues in radiation therapy. In this study, an experienced physicist evaluated the setup of the patients during treatments where many unexpected errors were observed. Methods- The physicist spent few hours a week in the treatment room and recorded any error that happened in the treatment setup from the physicist’s point of view. In some errors, a follow up dosimetry was performed to evaluate the effect of a specific error. Results- The errors were divided into a few categories. Out of 1000 patients in a 3 years period, various minor and major errors were observed for 115 patients. Most of the errors were in treatment field’s shape and size. There were also few mistakes made by technicians due to the lack of conceptual understanding particularly when the electron shield was placed too far from the skin. Results of film dosimetry revealed that this can cause a severe underdose of the tumor and an overdose of the shielded area. Conclusion- Many of the recorded setup errors in this study were related to the setup protocols for a particular center. However, there are many mistakes such as mistakes of the technicians and physicists that can be prevented with proper trainings. https://fbt.tums.ac.ir/index.php/fbt/article/view/64 https://fbt.tums.ac.ir/index.php/fbt/article/download/64/55