DEVICE FOR CORRELATING CT AND RADIATION-THERAPY PORTAL IMAGES

Algorithms currently being developed for CT reconstruction may yield attenuation coefficients, atomic number, or other physical properties of imaged structures which in turn may allow treatment planning and dose distribution studies incorporating homogeneity and contour corrections. A potential valuable feature for future development would be three-dimensional treatment planning systems. Basic to all these applications is the seemingly simple yet important problem of correlating CT transaxial scan levels with typical full-size radiographs encompassing the treatment volume as obtained from simulators, portal films, or routine diagnostic radiographic views. This paper describes a technique that can accomplish this correlation in a simple, straightforward, accurate manner. In addition, the device used minimizes the production of artefacts usually produced by inclusion of foreign objects into CT scan fields. Such artefacts hinder accurate tissue-boundary localization and also seriously hamper calculations using digital CT values for dose distribution studies.