Geant4-DNA vs FLUKA code

Respected Experts,

I have calculated microdosimetric quantity (yF and yD) for 40 keV photon using Geant4-DNA physics (“microyz” input example) in 1 um water sphere and for the same photon with FLUKA code using TEPC filled with TE-propane gas of density required for 1 um. But FLUKA calculated yD values is about 35% higher and yF values is about 40% higher as compared to Geant4-DNA physics based results.

However, for higher energy photon such as 100 keV and above, agreement of yF and yD based on Geant4-DNA and FLUKA is within 2-5 %.

Simulation setup is as below:

  1. For FLUKA, production and transport cuts are set at 1 keV (which is lowest available) and in Geant4-DNA (option_2) these are 10 eV.
  2. In FLUKA, parallel photon beam incident on TEPC placed in air whereas in “microyz” input point-isotropic photon source is placed at the centre of water-box.

What may be the probable cause for this large deviation in 40 keV photon or whether I am doing something wrong?

As you pointed out, you are comparing microdosimetric spectra, using Geant4-DNA which is a Track Structure approach and FLUKA, which is based on Condensed History Approach. The models are different, the cuts are different. So, depending on the radiation field and the size of the sensitive volume, I am not surprised if you get different results! Please, look at this paper:, which shows when track structure and condensed history approach converge to provide the same results: "Investigation of track structure and condensed history physics models " by Peter Lazarakis, Sebastien Incerti et al.