Recent advances in digital fluoroscopy have shown that good quality portal images can be produced instantaneously and continuously during high versatile imager which is easy to use and is readily acceptable by the radiation therapy community need to be developed. Since the modern radiation therapy machines are isocentric, the fluoroscopic imager has to be multi-directional. Building an imager which is mounted on the gantry of the therapy machine and which is to be retractable such that it would not interfere with patient setup is considered impractical in terms of cost effectiveness. This proposed research is to develop a bi-directional fluoroscopic imager with additional capability to image at a range of oblique angles. The latest image processing techniques will be incorporated into the micro-computer based system. Low contrast high energy x-ray images will be enhanced. A computer aided error detection and correction algorithm will be used to check and help correct patient portal alignment. A combined image and text handling database software will also be used for treatment review.