A Method to Model the X-ray Response of Electronic Portal Imaging Device

Electronic Portal Imaging Device (EPID) has been widely used in dose verification of radiotherapy. When using EPID for dose verification, it is necessary to calculate the primary and scatter rays in the EPID plane respectively. In our study, we use a series of measurement data to model the scatter to primary ratio (SPR) of EPID under different conditions. It is found that the SPR of EPID is related to the field size, phantom thickness, exit gap, and off-axis distance. In the process of treatment, the primary and scatter values of each point in EPID can be quickly calculated by the corresponding SPR. This method simplifies the modeling process of primary and scatter rays of EPID and improves the calculation accuracy of off-axis points.