A new workflow is proposed to update the intraoperative electron radiotherapy (IOERT) planning refreshing the position and orientation (pose) of a virtual applicator with respect to the preoperative computed tomography (CT) with the actual pose during surgery. The workflow proposed relies on a robust registration of the preoperative CT and intraoperative projection radiographs acquired with a C-arm system. The workflow initially performs a geometric calibration of the C-arm using fiducials placed on the applicator.