 The objective of this proposal is to test the clinical practicality of a new technology; cone beam imaging, for verification of treatment set up accuracy of cancer patients receiving radiation therapy. Currently, treatment accuracy is checked via use of 2-dimensional projection x-rays taken with the megavoltage treatment beam and electronic portal imaging devices EPID. Typically 2 orthogonal portal images are obtained to confirm patient positioning accuracy. This method of treatment verification, however, usually provides images of poor quality and lacks true 3D information, thus making it difficult for the radiation oncologist to definitively confirm treatment accuracy. New generation EPIDs are capable of obtaining higher quality images at significantly lower imaging doses. Thus, for the same total imaging dose new generation EPIDs permit acquisition of many projection images rather than just 2 or 3. The combination of more images and higher quality images should permit more definitive assessment of treatment accuracy. We propose here to test the clinical practicality and reliability of a new prototype portal imaging system. 