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 ability to provide direct and quick verification and monitoring of patients during both setup and treatment of breathing synchronized radiotherapy (BSRT, including breathing gated, voluntary and forced breath-hold radiotherapy treatment.) These limitations are largely due to their slow image capture rate and poor image quality. An amorphous silicon array flat panel electronic portal imaging device (si-EPID) is emerging to meet the challenge. The purpose of this study is threefold: (1) to characterize the performance of a prototype 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 detector array and Clinic accelerator at the University of California Davis Cancer Center were used for imaging. Three quality assurance phantoms: a Lutz PVC phantom, a modified "Las Vegas" phantom, and a RMI model 1151 phantom, were used to characterize the imaging system. A Rando head phantom was used for 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 application, two sets of si-EPID images were collected from a lung cancer patient 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 with 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 possible to collect the images at the beginning, middle, and end of each breath-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.

Early experience with the Varian Six Second body scanner in the diagnosis of hepatobiliary tract disease.

Thirty-four patients with liver disease were studied with a research model of the Varian Six Second body scanner. Useful information was gained in patients with a variety of hepatic disorders. This scanner permits resolution of normal hepatic parenchymal detail which has not been reported previously and has reduced the streak artifacts originating from high- and low-CT objects which have been a major source of image degradation with other units.

Stop-action cardiac computed tomography.

Computed tomographic (CT) cardiac imaging in vivo has been hampered by motion of the heart during its cardiac cycle. A technique of post data-acquisition correlation of the angular projection data using the electrocardiogram as a reference signal is described. This method produced seven "stop action" images of the heart and resulted in delineating morphological detail not recognizable on the conventional CT scan.