Rapid portal imaging with a high-efficiency, large field-of-view detector.
The design, construction, and performance evaluation of an electronic portal imaging device (EPID) are described. The EPID has the same imaging geometry as the current mirror-based systems except for the x-ray detection stage, where a two-dimensional (2D) array of 1 cm thick CsI(Tl) detector elements are utilized. The approximately 18% x-ray quantum efficiency of the scintillation detector and its 30 x 40 cm2 field-of-view at the isocenter are greater than other area-imaging EPIDs. The imaging issues addressed are theoretical and measured signal-to-noise ratio, linearity of the imaging chain, influence of frame-summing on image quality and image calibration. Portal images of test objects and a humanoid phantom are used to measure the performance of the system. An image quality similar to the current devices is achieved but with a lower dose. With approximately 1 cGy dose delivered by a 6 MV beam, a 2 mm diam structure of 1.3% contrast and an 18 mm diam object of 0.125% contrast can be resolved without using image-enhancement methods. A spatial resolution of about 2 mm at the isocenter is demonstrated. The capability of the system to perform fast sequential imaging, synchronized with the radiation pulses, makes it suitable for patient motion studies and verification of intensity-modulated beams as well as its application in cone-beam megavoltage computed tomography.
Mosleh-Shirazi
M A
MA
Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Trust, Sutton, Surrey, United Kingdom. aminm@rsch.org.uk
Evans
P M
PM
Swindell
W
W
Symonds-Tayler
J R
JR
Webb
S
S
Partridge
M
M
D004867:Equipment Design; D006801:Humans; D008962:Models, Theoretical; D019047:Phantoms, Imaging; D011880:Radiotherapy Planning, Computer-Assisted; D011882:Radiotherapy, High-Energy; D012588:Scintillation Counting / Q000295:instrumentation / Q000706:statistics & numerical data; D013679:Technology, Radiologic / Q000295:instrumentation* / Q000706:statistics & numerical data