Room: Exhibit Hall | Forum 9
Purpose: Monte Carlo (MC) studies of electronic portal imaging devices (EPIDs) have been hindered by the intensive computation time required. A novel method, based on energy deposition efficiency (Î·) and optical photon spread function (OSF), has been introduced to speed up the simulation while maintaining the same fidelity of the results.
Methods: A validated EPID model was built with Geant4 application for tomographic emission (GATE), including radiative and optical photon transport, as well as electronic noise. The â€œfast methodâ€? replaces optical transport with predetermined optical point spread functions. During fast simulation, the EPID model is replaced by a pixelated air slab. Detection of an incident X-ray with energy, E, is based on a random number generation (smaller than Î·(E)). If detected, OSF(E), the optical point spread function, was added to the final image. This fast method was validated against measurement and conventional (slow) simulation with modulation transfer function (MTF), measured with a collimated slit, and with signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and contrast measured with a Las Vegas phantom. Normalized mean-root-squared error (NMRSE) was calculated for MTF comparison, and percentage difference for SNR, CNR, and contrast. Computational time was compared between conventional and fast methods. Clinical application of the fast method was demonstrated using an anthropomorphic pelvis phantom.
Results: MTF of the fast method matches well with measurement (NMRSE 0.0165) and conventional method (NMRSE 0.0278). SNR, CNR, and contrast show good agreement, with differences of 0.64%-8.98% between fast method and measurement, and 2.24%-9.96% difference between fast and conventional methods. The fast method has shortened simulation time by a factor of 60.
Conclusion: A novel method, based on Î· and OSF, has been validated for fast and accurate MC simulation of EPID images. This method has the potential to accelerate novel imager development and evaluation, especially for multiple projection imaging.
Funding Support, Disclosures, and Conflict of Interest: This work was supported, in part, by award number R01CA188446 from the National Institutes of Health and a research grant from Varian Medical Systems, Inc.