State of the art in electronic detectors for portal imaging

Summary form only given. The first clinically-practical, electronic portal imaging devices, which were introduced over a decade ago, spurred the exploration of the role of digital imaging in localization and verification for radiotherapy. However, these technologies, based on lens and fiber-optic-coupled phosphor-camera systems and on liquid ionization chambers, generally fail to provide imaging performance equivalent to that of the current gold standard, radiotherapy film cassettes. While incremental improvements in these technologies have been achieved, these and other limitations have encouraged the development of fully solid-state, digital imagers based on thin-film electronics. This new technology, referred to as active matrix, flat-panel imagers (AMFPIs), employs large monolithic imaging arrays (presently, up to 40/spl times/40 cm) and provides image quality superior to that of conventional film systems. AMFPIs are compact, allow radiographic or fluoroscopic readout, and provide images exhibiting a high degree of spatial and contrast information content over a wide range of doses and therapy energies. This technology also lends itself to diagnostic projection and CT imaging as well as dosimetry-all of which are being examined in the context of treatment room needs. In this presentation, the current status of electronic detectors for portal imaging is reviewed and anticipated future developments are discussed.