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BEST IN PHYSICS (JOINT IMAGING-THERAPY): Optimizing a Layered Detector Design for Megavoltage Spectral Imaging

M Myronakis

M Myronakis1*, J Rottmann1 , Y Hu2 , P Baturin3 , A Wang3 , P Huber4 , R Fueglistaller4 , D Morf4 , J Star-Lack3 , R Berbeco1 , (1) Brigham and Women's Hospital, Boston, MA, (2) Dana Farber Cancer Institute, Boston, MA, (3) Varian Medical Systems, Palo Alto, California, (4) Varian Medical Systems, Baden, Dattwil


WE-F-605-6 (Wednesday, August 2, 2017) 1:45 PM - 3:45 PM Room: 605

Purpose: The overall goal of this project is spectral imaging by energy separation of clinical MV photon beams accomplished through the use of layered detectors with different energy absorption characteristics. The objectives of this work are a) to determine the energy separation between absorption spectra at each detector layer that maximizes contrast-to-noise (CNR) ratio on a weighted subtracted image and b) to suggest an optimal layered-detector design based on this separation.

Methods: The clinical tasks modeled were bone suppression and gold fiducial enhancement. CNR and contrast (Cs) were evaluated for a digital phantom consisting of 5cm bone and 1mm gold fiducial within 20cm soft-tissue. CNR of bone (CNRb) and bone plus gold (CNRbAu) were estimated assuming two detector layers, each with a mean absorption energy (E1 and E2) and a quantum efficiency (n) of 1.2%. E1 and E2 were iteratively varied; at each iteration CNRb and CNRbAu were calculated on the weighted image of the two layers. The maximum CNR difference (dCNR) between CNRb and CNRbAu while CNRb was minimized, was recorded at each energy. Monte Carlo simulations of various scintillator materials with absorption characteristics within the energy range obtained from the analytical calculations, were carried out to determine the optimal layered detector configuration.

Results: The maximum CNR difference (dCNR) depended on E1, E2 and n. dCNR peaked at E1=0.19MeV, increased exponentially with increasing E1 and E2 separation and reached a plateau of 5.8 at E2=1.25MeV. Monte Carlo simulations of Gd2O2S, BGO, ZnSe and LKH5 showed that a two-layer detector utilizing GOS and LKH5 will have the appropriate absorption characteristics for MV spectral imaging.

Conclusion: An appropriate detector configuration for MV spectral imaging using multi-layer design was determined, based on CNR and energy separation characteristics. Future work will include Monte Carlo and experimental validation of the proposed detector configuration.

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