Evaluation of an electronic portal imaging device (target view, ge) as a quality assurance tool

Summary Purpose A proper control of the geometrical accuracy of treated portals during radiotherapy results in higher quality of treatment and may lead to the increase in the therapeutic gain. In this work, an evaluation of an electronic portal imaging device (EPID) was made in the following aspects: the quality of images, the estimation of prolongation of the treatment, and the corrections introduced after EPIDs. Material and methods We have archived 2430 portal images of 184 patients who were irradiated at our department. The following significant errors were established: a shift in the field along x, y, z axes (more than 5 mm in the head and neck region, more than 7 mm in the chest tumours and 10 mm in pelvic region), a displacement of shield by the same values, and an erroneous field size assigment by more than 10 mm. Results The introduction of the EPID into clinical practice involved approximately 10% of the session time. The quality of the electronic portal images received was acceptable for further analysis in 87% of the analysed group of patients. Significant errors have been registered in 33% of monitored patients. Prior to the treatment and during the set-up procedure, corrections were made in 20% of the evaluated patients. Conclusions An electronic portal imaging device (EPID) is a useful tool for fast and reliable portal image acquisition.