Potential and role of a prototype amorphous silicon array electronic portal imaging device in breathing synchronized radiotherapy

Current electronic portal imaging devices (EPID) are limited in their abili ty to provide direct and quick verification and monitoring of patients duri ng both setup and treatment of breathing synchronized radiotherapy (BSRT, i ncluding breathing gated, voluntary and forced breath-hold radiotherapy tre atment.) These limitations are largely due to their slow image capture rate and poor image quality. An amorphous silicon array Bat panel electronic po rtal imaging device (si-EPID) is emerging to meet the challenge. The purpos e of this study is threefold: (1) to characterize the performance of a prot otype si-EPID; (2) to compare image quality against that of digitized films ; and (3) to evaluate the device in terms of verification of patient setup and monitoring during BSRT. In this study a Varian prototype si-EPID detect or array and Clinic accelerator at the University of California Davis Cance r Center were used for imaging. Three quality assurance phantoms: a Lutz PV C phantom, a modified "Las Vegas" phantom, and a RMI model 1151 phantom, we re used to characterize the imaging system. A Rando head phantom was used f or anthropomorphic imaging tests. Images were obtained with the si-EPID and a Fuji RX film in a Kodak X-Omatic cassette. To investigate the clinical a pplication, two sets of si-EPID images were collected from a lung cancer pa tient during a 22 s breath-hold and normal breathing. The quality of images obtained with the fast mode was found to be comparable to that obtained wi th the digitized films. The images with the standard mode were found to be better than the digitized film images. With this prototype si-EPID, it is p ossible to collect the images at the beginning, middle, and end of each bre ath-hold for those patients who can hold their breath for longer than 15 s. The si-EPID images can provide a quick verification of the initial patient setup and subsequent treatment position throughout the daily fractionation . (C) 1999 American Association of Physicists in Medicine. [S0094-2405(99)0 2011-8].