Port films are routinely exposed during radiotherapy treatment to verify correct patient positioning. Contrast is always poor, due to the high energy of the radiation, and spatial resolution is seriously degraded by scatter and large penumbra. We place port films on an illuminated panel facing a vidicon camera, and obtain digitized images for processing in our DICOM-8 digital imaging computer. Averaging up to 256 frames reduces camera noise. Convolution filtering, windowing, histogram equalization and blurred mask subtraction lead to significant improvement in the perception of anatomical structures. Digitization of the x-ray simulator film, using real-time subtraction for accurate alignment, permits the direct comparison of the actual field size with the prescribed treatment area.