EVALUATION OF ELECTRONIC PORTAL IMAGING DEVICE FOR MISSING TISSUE COMPENSATOR DESIGN AND VERIFICATION

The purpose of this investigation is to determine if electronic portal imaging devices (EPIDs) can be used for the design and verification o f compensating filters. In order to do this, we investigated the opera ting characteristics of a commercially available EPID and the variatio n in transmitted dose for various measurement situations. We performed four initial tests to determine the EPID response specific to compens ator situations. The tests determined EPID response to variable patien t SSDs, different gantry angles, positions of an inhomogeneity within a phantom, and the sensitivity variation of different parts of the ima ger. After these tests, we determined the attenuation functions relati ng EPID response to phantom thickness for various phantom materials. W ith these functions, we tested simple compensation situations to demon strate that missing tissue compensators can both be designed and verif ied using EPIDs.