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Comparison between EGSnrc, GEANT4, MCNP and Penelope for photon and electron beams

Kolloquium der Abteilung 6

A status report on the agreement between four publicly available Monte Carlo simulation packages for situations involving photon and electron beams is presented. Results from the AAPM TG-195 “Monte Carlo Reference Data Sets for Imaging Research” are reviewed. Six different cases involving photon beams were simulated with EGSnrc, GEANT, MCNP and Penelope. Since no experimental validation was undertaken, this comparison allows only an estimation of the level of agreement among these codes. Differences were below 2 % for most of the cases. Most of these differences are due to the use of different incoherent scattering models in the codes. The largest discrepancies were observed in the x-ray production case, where differences ranged between 10 % and 20 %. Using electron pencil beams of 0.5 MeV, 1 MeV and 5 MeV, the accuracy of the electron transport in these codes is tested against their own single scattering mode (SS) for energy deposition in a water sphere. The sphere is in one case in vacuum and in another surrounded by air and the radius is allowed to vary. The choice of such a simple geometry allows the focus to be placed on the physics models. Differences of up to a factor of 7 were found for 0.5 MeV electron beams and the smallest radii when using default settings in some of the best parameters reproducing the SS results demonstrates the varying degrees of electron step-size dependency of these codes.