Validation of a Monte Carlo Model of a Dual-Layer Flat-Panel Detector
Abstract
Purpose
To develop and validate a Monte Carlo model of a dual-layer flat-panel detector for image-guided radiotherapy applications; to optimize the design and material composition to improve spectral separation while maintaining clinically acceptable image quality.
Methods
A dual-layer flat-panel detector is modelled in TOPAS, an extension wrapping GEANT4. The detector stack includes top and bottom scintillation and readout layers separated by structural supports and adhesives. A focused anti-scatter grid is also modelled. The model is validated against simulation results from the literature. Multiple detector configurations are simulated by varying the materials and thicknesses of the bottom scintillator. Detector performance is evaluated using the MTF50 and the DQE(0), which establishes a multiparameter space for detector optimization. The MTF is derived from a slanted edge technique and a precomputed incident spectrum consistent with RQA 9. The DQE(0) is computed using the Swank formalism.
Results
Validation against previous literature yielded NRMSEs over frequencies from 0 to 3.5 mm-1 of 0.007 and 0.016 for the MTF curves of the top and bottom layers, respectively. Varying the bottom scintillator thickness from 400 to 800 μm increased the DQE(0) from 0.09 to 0.13 and decreased the MTF50 from 1.01 to 0.74 mm-1. A comparative analysis of the MTF, DQE, and energy separation is in progress.
Conclusion
This work developed and preliminarily validated a Monte Carlo model of a dual-layer flat-panel detector and simulated DQE and MTF spaces to optimize spectral separation on the bottom detector layer. Using these parameters, this work identified opportunities for further optimizing the material and thickness configurations of the two scintillation layers. The detector simulation framework will be used in future investigations, including the evaluation of anatomical phantoms and the reduction of imaging artifacts.