WE‐DE‐BRA‐04: A Cost‐Effective Pixelated EPID Scintillator for Enhanced Contrast and DQE

Abstract

Purpose:Beams‐eye‐view imaging applications such as real‐time soft‐tissue motion estimation and MV‐CBCT are hindered by the inherently low image contrast of electronic portal imaging devices (EPID) currently in clinical use. We investigate a cost effective scintillating glass that provides substantially increased detective quantum efficiency (DQE) and contrast to noise ratio (CNR).Methods:A pixelated scintillator prototype was built from LKH‐5 glass. The array is 12mm thick; 42.4×42.4cm2 wide and features 1.51mm pixel pitch with 20µm separation (glue+septa). The LKH‐5 array was mounted on the active matrix flat panel imager (AMPFI) of an AS‐1200 (Varian) with the GdO2S2:Tb removed. A second AS‐1200 was utilized as reference detector. The prototype EPID was characterized in terms of CNR, modulation transfer function (MTF) and DQE. Additionally, the visibility of various fiducial markers typically used in the clinic as well as a realistic 3D‐printed lung tumor model was assessed. All items were placed in a 12cm thick solid water phantom. CNR is estimated using a Las Vegas contrast phantom, presampled MTF is estimated using a slanted slit technique and the DQE is calculated from measured normalized noise power spectra (NPS) and the MTF.Results:DQE(0) for the LKH‐5 prototype increased by a factor of 8× to about 10%, compared to the AS‐1200 equipped with its standard GdO2S2:Tb scintillator. CNR increased by a factor of 5.3×. Due to the pixel size the MTF50 decreased by about 55% to 0.23lp/mm. The visibility of all fiducial markers as well as the tumor model were however markedly improved in comparison to an acquisition with the same parameters using the GdO2S2:Tb scintillator.Conclusion:LKH‐5 scintillating glasses allow the cost effective construction of thick pixelated scintillators for portal imaging which can yield a substantial increase in DQE and CNR. Soft tissue and fiducial marker visibility was found to be markedly improved.The project was supported in part by NIH grant R01CA188446‐01 and a grant from Varian Medical Systems.