A COMPREHENSIVE SYSTEM FOR THE ANALYSIS OF PORTAL IMAGES

In recent years, several techniques for the processing and analysis of portal images have been developed. It is the aim of this study to integrate some of these techniques into one comprehensive system. An advantage of this approach is that clinical experience can be obtained with more than one technique and a comparison of the techniques becomes possible. The portal image analysis procedure is implemented in the following steps: preparation of the reference image, portal image field edge detection, field edge match, anatomy match and the presentation of the results. For most of these steps, several alternative methods (e.g., interactive and automatic) are implemented. In addition, two new visualisation techniques have been incorporated. The first is a method for combining the results of the analysis of multiple fields in two dimensions, e.g., large and boost fields. The second is a method for three-dimensional reconstruction of beam setup data, as derived from portal image analysis, on arbitrary reconstructed slices of a CT scan. With the latter method, the effect of setup errors on complex treatments (e.g., matching fields) can be studied. The new system has been in clinical use in our institution for two years and has been used to analyse about 5000 clinical portal images. The operators could choose freely from several matching methods. For 83% of the images our automatic matching algorithm was used. When required, the result of this method was corrected using the interactive drawing on image match. Significant corrections (more than 1 mm translation or 1 degree rotation) were applied to 27% of the automatically analysed images. The remaining images were mostly analysed directly using the interactive drawing on image match (15%) or using the interactive image on image match (2%). Point and line match methods, although implemented, were hardly used by the operators.