An on-line electronic portal imaging system for external beam radiotherapy

A digital imaging system has been constructed to obtain the treatment portal image of a patient during external beam radiotherapy. A DEC LSI-11/23 microcomputer controls a stepper motor, which moves a linear array of 256 silicon diodes to scan the radiation transmitted through the patient. The computer also processes the collected data to generate an image for displaying on a video monitor. The quality of the digital image is comparable to that of the conventional verification radiographs. Major advantages of the system include the speed and simplicity in data storage and retrieval and in its capability of direct comparison with simulation radiographs.