Electronic portal imaging device (EPID) images are converted to an absolute dose at a simulated absolute dose plane in a measurement phantom for supporting intensity modulated radio therapy (IMRT) dose quality assurance (QA) by geometrically projecting the EPID image as may be needed, generating an output factor correction map specific to a radiation treatment beam, multiplying an EPID image by the output factor correction map for generating an output corrected EPID image, and convolving the output corrected EPID image with a redistribution kernel for generating a relative dose at a preselected dose plane. A wide field calibration map is then applied to the relative dose for generating an absolute dose at the preselected dose plane location.
