The construction of phantoms for testing imaging parameters has been well documented in the literature. As computers have been introduced into the different areas of medicine, they have become more and more relied upon to replace conventional technologies. One specific example is that of plane film X-rays. Digitally Reconstructed Radiographs (DRR's) are computer generated images that are generated from a 3 D volume of data, such as CT or MRI axial scans, and can be used in place of conventional X rays. The computer can generate a DRR image for any position, orientation and magnification, and geometries not physically possible in the real world. In this work a technique is developed to generate phantoms that can be used for testing the accuracy of DRR's. A computer generated phantom can produce multiple test cases that can be used to test specific variables of the DRR's. A series of 12 different standard phantoms were used to test the ability of three different commercially available treatment planning or virtual simulation systems to generate DRR's. A virtual simulation system under development by the author and collaborators and seeking approval from the Food and Drug Administration (FDA), was used as a development platform for this work. Initial evaluation of the usefulness of the digital phantoms for testing showed immediate results. The first virtual simulation system tested with the phantoms revealed a major error in its ability to generate accurate DRR's. Subsequently tests of the three commercially available systems further demonstrated the usefulness of the work. The tests revealed errors in two of the three systems evaluated but it was determined that they were not clinically significant. In conclusion, the digital phantoms developed in this work are a fast, accurate method for testing digitally reconstructed radiographs. It is an extremely versatile testing method, as the phantoms can be generated with ease for any geometry without needing access to a CT scanner. This method of testing can be used to test a number of different DRR image parameters. Should an error be found, it can be used to isolate errors that might exist in the imaging device. It is an extremely versatile testing method, as the phantoms can be generated with ease for any geometry without needing access to a CT scanner. This method of testing can be used to test a number of different DRR image parameters. Should an error be found, it can be used to isolate errors that might exist in the imaging device.