“…The aS500 EPID has been shown to have a nonlinear signal response to radiation, 25,26,9,12 and the EPID's response over a range of doses relevant to IMRT was again measured in this work. Several open-field irradiations were delivered, and EPID images were acquired in "integrated image" mode, where the true pixel values were restored by multiplying the frame-averaged image by the number of frames.…”