Comparison of microdosimetric simulations using PENELOPE and PITS for a 25 keV electron microbeam in water

The calculations presented compare the performances of two Monte Carlo codes used for the estimation of microdosimetric quantities: Positive Ion Track Structure code (PITS) and a main user-code based on the PENetration and Energy LOss of Positrons and Electrons code (PENELOPE-2000). Event by event track-structure codes like PITS are considered superior for microdosimetric applications and they are written for this purpose. PITS tracks electrons in water down to 10 eV. PENELOPE is one of the few, among widely available general purpose codes, that can simulate random electron-photon showers in any material for energies from 100eV to 1GeV. The model for the comparison is a large water cylinder with an internal scoring geometry of spheres with 1(micro)m diameter where the scoring quantities are calculated. The source is a 25 keV electron pencil beam impinging normally on the sphere surface. This work shows only the lineal energy as a function of position and lineal energy spectra at a given location since for microdosimetry and biology applications, and for discussion of radiation quality in general, these answers are more appropriate. The computed PENELOPE results are in agreement with those obtained with the PITS code and previously published in this journal. This paper demonstrates PENELOPE's usefulness at low energies and for small geometries. What is still needed are experimental results to confirm these analyses