Basic Dose Response of Fluorescent Screen-bas d Potal Imaging Device

Purpose: The purpose of this study is to investigate fundamental aspects of the dose response of fluorescent screen-ba ed lectronic portal imaging devices (EPIDs). Materials and Methods: We acquired scanned signal across portal planes as we varied the radiation that entered the EPID by changing the thickness and anatomy of the phantom as well as the air gap between the phantom and the EPID. In addition, we simul ted the relative contribution of the scintillation light signal in the EPID system Results: We have shown that the dose profile across portal planes is a function of the air gap and phantom thickness. We have also found that depending on the density cnge with the p antom geometry, errors associated with dose response based on the EPID scan can be as high as 7%. We also found that scintillation light scattering within the EPID system is an important source of error. Conclusion: This study revealed and demonstrated fundamental characteristics of dose response of EPID, as relative to that of ion chambers. This study showed that EPID based on fluorescent screen cannot be an accurate dosimetry system