A simple system for detecting patient movement during radiation therapy

The authors described a system which detects patient movement while that patient is undergoing radiation treatment. The system consists of simple and inexpensive electronic circuitry using the laser localization lights commonly used with an isocentric linear accelerator. If the patient moves, a visual or audible signal alerts the radiation-therapy technologist who can interrupt treatment and reposition the patient. The verification of proper patient position using this technique compares favorably with the routine use of cerification radiographs.