What is Electronic Portal Imaging

This chapter presents an overview of the procedures that are used for the verification of the patient position during radiotherapy. Furthermore, a method for the verification of the radiotherapy isocenter prior to treatment delivery is proposed. The method is based on the alignment of two Computed Tomography (CT) scans: a scan, which is acquired for treatment planning, and an additional verification scan, which is acquired prior to the treatment delivery. The proposed method was applied to CT scans, acquired from 20 patients with abdominal tumors and 20 patients with breast/lung cancer. The results of the proposed method were compared with the ones obtained using conventional methods, indicating that the estimated isocenter displacement can be translated into patient setup error inside the treatment room.