Using the Dosimetry Check IMRT QA package a deconvolution kernel to be used in exit image dose calculations was created. This kernel modeled Electronic Portal Imaging Device response by incorporating the various machine characteristics along with the variant patient thickness and composition. To properly achieve this, Dosimetry Check first had to accurately model the beams for the machines being used. This was done by taking a series of in air and in water measurements including central axis depth dose values at various field sizes and in-air off center ratios to model beam flatness and symmetry. A deconvolution kernel for patient CT dose computation using pre-treatment (in-air) EPID images was created. This baseline helped establish the necessary measurements for the exit image kernel. The necessary measurements for the exit image kernel included EPID images of various field sizes with various thicknesses of water in the beam as well as a characterization of off axis narrow beam transmission. The fit was performed and a report generated for its variance. The kernel was then successfully used in the evaluation of an IMRT prostate plan that was created for an anthropomorphic phantom and compared to a baseline evaluation of the same plan using in air EPID images. Volumetric, planar, and point dose comparison between measured and computed dose distributions agreed favorably indicating the validity of technique used for IMRT QA.