Comparing water to DNA for simulation of Auger electron direct damage to DNA using Geant4

Typically water is used as an analog material for Deoxyribonucleic Acid (DNA) in Monte Carlo simulations of biological radiation interactions. Prior to this work, it was unclear whether water is an appropriate stand-in for DNA when simulating direct radiation damage on the nano scale. The increased interest in targeted tumor therapy using Auger electrons has requires an understand of the radiobological effectiveness of low energy electrons. A chromatin fiber was constructed within the Geant4 simulation toolkit down to the molecular level. The Binary Encounter Bethe (BEB) model for electron impact ionization was added to the Geant4 Toolkit so the cross sections of molecules could be more accurately modeled. Validation was performed by comparing the BEB model to the ab initio Born model already implemented in Geant4. The BEB produces less ionization events but is effective at comparing DNA to water in this context by providing order-of-magnitude similarities in the results. Using the BEB model the number of double strand breaks for DNA was shown to be much greater than for water, indicating that water is not an effective analog for DNA.