Danut Ilas, Mark L. Williams, Douglas E. Peplow, and Bernadette L. Kirk
Oak Ridge National Laboratory, Oak Ridge, TN


"Multidimensional Coupled Photon-Electron Transport Simulations using Neutral Particle SN Codes"

in the CD-ROM proceedings of the
American Nuclear Society's
Computational Medical Physics Working Group Workshop II
University of Florida, Gainesville, FL, September 30 -October 3, 2007.


View PDF, Abstract PDF, Ilas's Presentation Slides, OSTI Information Bridge



ABSTRACT

During the past two years, a study has been under way at Oak Ridge National Laboratory to assess the suitability of the popular SN neutral particle codes ANISN, DORT, and TORT for coupled photon-electron calculations specific to external beam therapy for medical physics applications. The CEPXS-BFP code was used to generate the cross sections. The computational tests were performed on phantoms typical of those used in medical physics for external beam therapy, with materials simulated by water at different densities, and the comparisons were made against Monte Carlo simulations that served as benchmarks.

Although the results for one-dimensional calculations were encouraging, it appeared that the higher-dimensional transport codes had fundamental difficulties in handling the electron transport. The results of two-dimensional simulations using the code DORT with an S16 fully symmetric quadrature set agree fairly with the reference Monte Carlo results but not well enough for clinical applications. While the photon fluxes are in better agreement (generally, within less than 5% from the reference), the discrepancy increases, sometimes very significantly, for the electron fluxes. The paper, however, focuses on the results obtained with the three-dimensional code TORT, which had convergence difficulties for the electron groups. Numerical instabilities occurred in these groups. These instabilities were more pronounced with the degree of anisotropy of the problem.

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