A multipurpose phantom for use with electronic portal imaging devices.

A simple, low-cost, multipurpose phantom has been designed for use with electronic portal imaging devices (EPIDS). Making use of the high spatial resolution of an EPID, together with the built in software tools for measuring distances, it is possible to verify x-ray/light field size and congruence, at any gantry angle, for fields up to 200 mm x 200 mm. Being of an accurate construction, it can help analyse the distance measuring capabilities of an EPID, ensuring that they are accurate and remain so with time. It can also be used to quantify, and monitor, image displacement and rotation with gantry angle.