title: In silico investigation of factors affecting the MV imaging performance of a novel water-equivalent EPID.
abstract: OBJECTIVE
  A Geant4 model of a novel, water-equivalent electronic portal imaging device (EPID) prototype for radiotherapy imaging and dosimetry utilising an array of plastic scintillating fibres (PSFs) has been developed. Monte Carlo (MC) simulations were performed to quantify the PSF-EPID imaging performance and to investigate design aspects affecting performance for optimisation.
  
  
  METHODS
  Using the Geant4 model, the PSF-EPID's imaging performance for 6 MV photon beams was quantified in terms of its modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE). Model parameters, including fibre dimensions, optical cladding reflectivity and scintillation yield, were varied to investigate impact on imaging performance.
  
  
  RESULTS
  The MC-calculated DQE(0) for the reference PSF-EPID geometry employing 30mm fibres was approximately nine times greater than values reported for commercial EPIDs. When using 10mm long fibres, the PSF-EPID DQE(0) was still approximately three times greater than that of a commercial EPID. Increased fibre length, cladding reflectivity and scintillation yield produced the greatest decreases in NPS and increases in DQE.
  
  
  CONCLUSIONS
  The potential to develop an optimised next-generation water-equivalent EPID with MV imaging performance at least comparable to commercial EPIDs has been demonstrated. Factors most important for optimising prototype design include fibre length, cladding reflectivity and scintillation yield.
authors.affiliation: Institute of Medical Physics, School of Physics, University of Sydney, Sydney, NSW 2006, Australia; Ingham Institute for Applied Medical Research, Sydney, NSW 2170, Australia. Electronic address: samuel.blake@sydney.edu.au.
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Blake
authors.affiliation: Institute of Medical Physics, School of Physics, University of Sydney, Sydney, NSW 2006, Australia; Ingham Institute for Applied Medical Research, Sydney, NSW 2170, Australia. Electronic address: j.cheng@physics.usyd.edu.au.
authors.forename: Zhangkai
authors.initials: Z
authors.lastname: Cheng
authors.affiliation: Institute of Photonics and Optical Science, School of Physics, University of Sydney, Sydney, NSW 2006, Australia. Electronic address: shaghik.atakaramians@sydney.edu.au.
authors.forename: Shaghik
authors.initials: S
authors.lastname: Atakaramians
authors.affiliation: Faculty of Health Sciences & Brain and Mind Centre, University of Sydney, Sydney, NSW 2006, Australia. Electronic address: steven.meikle@sydney.edu.au.
authors.forename: Steven
authors.initials: S
authors.lastname: Meikle
authors.affiliation: PerkinElmer Medical Imaging, Santa Clara, USA. Electronic address: minghui.lu@perkinelmer.com.
authors.forename: Minghui
authors.initials: M
authors.lastname: Lu
authors.affiliation: Institute of Medical Physics, School of Physics, University of Sydney, Sydney, NSW 2006, Australia; Ingham Institute for Applied Medical Research, Sydney, NSW 2170, Australia; Liverpool and Macarthur Cancer Therapy Centres, Sydney, NSW 2170, Australia. Electronic address: philip.vial@sswahs.nsw.gov.au.
authors.forename: Philip
authors.initials: P
authors.lastname: Vial
authors.affiliation: Institute of Medical Physics, School of Physics, University of Sydney, Sydney, NSW 2006, Australia. Electronic address: zdenka.kuncic@sydney.edu.au.
authors.forename: Zdenka
authors.initials: Z
authors.lastname: Kuncic
mesh_terms: D003198:Computer Simulation; D003952:Diagnostic Imaging / Q000295:instrumentation*; D055615:Electrical Equipment and Supplies; D009010:Monte Carlo Method; D055620:Optical Phenomena; D011874:Radiometry; D059629:Signal-To-Noise Ratio; D014867:Water
chemical_list: D014867:Water
keywords: EPID; Geant4; Monte Carlo