Design Optimization Studies for Active Matrix Flat Panel Imagers Based on Segmented Crystalline Scintillators for Radiotherapy Imaging.

Abstract

In this dissertation, a series of theoretical studies were performed using Monte Carlo simulation to optimize the design of active matrix flat panel imagers (AMFPIs) based on segmented scintillators for radiotherapy imaging. The influence of imager design specifications (such as use of a focused geometry, as well as the physical size and optical properties of scintillator elements) on imaging performance at megavoltage (MV) energies has been systematically investigated.

The first study, involving simulation of radiation transport only, examined focused segmented scintillators as a potential solution to counter the detrimental effect of beam divergence. A focused planar geometry was found to effectively eliminate degradation in spatial resolution and detective quantum efficiency due to beam divergence, and to achieve uniform imaging performance across the entire detection area for thick, large-area, segmented scintillators.

The second study, which involved simulation of both radiation and optical transport using a novel hybrid modeling technique, was performed to examine the influence of optical effects on the imaging performance of segmented scintillators. Based on the theoretical examination of various scintillator designs, an optimization map, which takes into account contrast-to-noise ratio and spatial resolution performance, was generated to guide decision-making in scintillator design.

The final study explored the possibility of extending the clinical application of thick, segmented scintillators to include kilovoltage (kV) imaging using an extended hybrid modeling technique. A methodology was presented for identifying the most favorable design of a dual energy imager based on segmented scintillators. Such a design maintains the desirably high level of imaging performance at MV energies made possible by thick, segmented scintillators, while helping to provide performance comparable to that of commercial imagers at kV energies.

The studies presented in this dissertation, which build upon the results of earlier empirical and theoretical characterizations of engineering prototypes, provide valuable insight for the design of future prototypes. It is anticipated that, through careful design assisted by theoretical modeling and empirical measurements, AMFPIs based on segmented scintillators can provide significantly improved performance compared to that of existing imagers in the treatment room, thereby increasing the clinical utility of in-room kV and MV imaging.