A next-generation electronic portal imaging device for simultaneous imaging and dosimetry in radiotherapy

Abstract

The aim of this thesis is to develop a next-generation Electronic Portal Imaging Device (EPID) for simultaneous megavoltage imaging and dosimetry in radiotherapy. The results of this thesis include the identification of a clinically implementable pixel sensitivity correction technique for a water equivalent EPID. This is important for clinical translation of this new technology. The imaging performance of an existing water equivalent EPID prototype previously developed by our group has been measured and characterised for the first time. The zero-frequency detective quantum efficiency (DQE) was found to be ~3%, which is a factor of three better than standard clinical EPIDs, which are not water-equivalent. A new design is proposed for further gains in imaging performance based on an array of air-clad optical fibres, and a fabrication method based on extrusion and fibre drawing has been developed and evaluated. Using finite element modelling simulations, a novel method is investigated for enhancing light output from the plastic scintillator array EPID. This method is based on inserting a nano-structured layer at the scintillator-detector interface, to maximize light transmission through the boundary. Overall, the work presented in this thesis demonstrates the feasibility of a next-generation EPID for clinical radiotherapy, with enhanced performance compared to standard clinical EPIDs.