A video-based patient contour acquisition system for the design of radiotherapy compensators

Recent advances in computer and video technology have enabled significant advances in the field of surface topography measurement. This paper will describe a digital video patient contour acquisition system for the design of radiotherapy beam compensators. The system is mounted on a tray which slides into the collimator of a radiotherapy simulator. The tray holds a source which projects a 1-mm wide fan beam of light along the simulator beam axis onto the patient. The tray also holds a small solid state video camera which views the projected line of light on the patient surface. Video images are digitized and processed on an 80386 based IBM PC-compatible computer. Transverse contours are obtained from one digitized video image or, in case of opposed fields, from two or more image frames taken at different gantry angles. Entire surfaces are measured by scanning the bed longitudinally and acquiring a number of transverse contours. Posterior surfaces are obtained by scanning a mold. A printer produces a template for making the compensator from sheet lead.