Application of the Single-Shot Dual-Detector Subtraction Technique to Portal Image Acquisition

Abstract

We have proposed the new image processing technique for portal images. The aim of the present study was to evaluate the clinical efficacy of the single-shot dual-detector subtraction technique to portal image acquisition. We prepared two storage phosphor plates for this study. A 1-mm-thick tungsten sheet was placed between the two storage phosphor plates. A portal image of high contrast is obtained using the back storage phosphor plate with a metal plate (i.e., a standard image).The front storage phosphor plate without a metal plate generates a portal image of low contrast. A bone-enhanced image is created by image subtraction between these two images. We visually evaluated the image quality of bone enhanced images and standard images using a Rando phantom. The treatment sites were the brain, lung, and pelvis of a Rando phantom. The observers were 10 radiation therapists. The criterion of evaluation was whether the vertebrae or bony structure as landmarks were clear. Each set images were evaluated as being superior, inferior or similar. When there was a difference in the evaluation, 2 points were given to the superior image, and 0 points were given to the inferior image. One point was given to each when both images were evaluated as being similar. The sign test was used to calculate differences based on theses scores, and image quality was evaluated using a two-sided test at a 5% level of significance. In all sites, many observers judged that the bone-enhanced images were superior to the standard images. The sign test revealed significant differences between the bone-enhanced images and the standard images at all sites (p<0.01). The bone-enhanced images obtained using our technique increased the image quality in terms of bone visibility and are useful for routine clinical practice.Keywordssingle-shot dual-detector subtractionportal imagestorage phosphor platebone-enhanced imagestandard image