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Comparison of Microdosimetric Quantities Calculated Using the Track Structure Monte Carlo Algorithms Geant4-DNA and NOREC

J Lucido

J Lucido1*, I Popescu2 , V Moiseenko3 , (1) University of Colorado School of Medicine, Aurora, CO, (2) British Columbia Cancer Agency, Vancouver, BC, (3) University of California, San Diego, La Jolla, CA


SU-E-T-81 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Microdosimetric quantities, such as the lineal energy, have been shown to correlate with the biological response to radiation and the relative biological effect of different radiation types. Track-structure Monte Carlo simulations are an important tool for investigating these responses and for developing mechanistic models to explain them. However, some of the cross-sectional data used in these algorithms has large uncertainties; thus, it is important to investigate how the implementation of the different codes affects the quantities of interest.

Two of the most widely-used publicly available track-structure Monte Carlo codes, Geant4-DNA and NOREC, were used generate electron tracks for two particle sources. One source was a mono-energetic parallel beam of electrons with energies from 5 to 500-keV, and the lineal energy for each track was calculated in 1-mm-spheres arranged in planar arrays at multiple distances from the source. The second source was mono-energetic, uniformly-distributed, and isotropic source, and the lineal energy was scored in a single 30-mm-sphere for energies between 300-eV and 5-keV.

The dose-mean lineal energy for the parallel-beam simulations almost all agreed within 5%. For the uniformly-distributed source, at the lowest energies there was strong agreement between the algorithms, but the Geant4-DNA simulations showed slightly more high-energy events for more energetic electrons, but the dose-mean lineal energy agreed to within 4% for all energies.

While there were slight differences in the results between the codes, these were consistent with previous studies of the stopping power and angular scattering distributions. Importantly, the computation time for Geant4-DNA was larger than for NOREC, largely due to approximations used in the NOREC for energies below 10-eV. This study shows that these approximation does not have a major impact on the microdosimetry on the energy and length scales investigated.

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