Original paperIn silico investigation of factors affecting the MV imaging performance of a novel water-equivalent EPID

- Image performance of a novel EPID model was quantified in terms of MTF, NPS and DQE.
- Geometry and physical properties were varied to quantify impact on above metrics.
- DQE(0) for reference geometry was 9%, nine times greater than for commercial EPID.
- Detector sensitivity increased with reflective components surrounding fibre cores.
- Increasing scintillation yield decreased NPS and increased DQE.

PurposeA 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.MethodsUsing 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.ResultsThe MC-calculated DQE(0) for the reference PSF-EPID geometry employing 30 mm fibres was approximately nine times greater than values reported for commercial EPIDs. When using 10 mm 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.ConclusionsThe 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.