Track structure simulations of proximity functions in liquid water using the Geant4-DNA toolkit

Abstract

The mechanistic Monte Carlo modeling of biological effects of ionising radiation at sub-cellular and DNA scale requires the accurate simulation of track structures in the biological medium, commonly approximated as liquid water. The formalism of microdosimetry allows one to describe quantitatively the spatial distribution of energy deposition in the irradiated medium, which is known to relate to the deleterious effects in the irradiated cellular targets. The Geant4-DNA extension of the Geant4 opensource and general-purpose Monte Carlo simulation toolkit has been recently evaluated for the simulation of microdosimetry spectra, allowing, in particular, the calculation of lineal energy distributions. In this work, we extend the microdosimetric functionalities of Geant4-DNA by the development of a new Geant4-DNA example dedicated to the simulation of differential proximity functions. Simulation results are presented for the proximity function of electrons, protons, and alpha particles over a wide energy range using the different physical models of electron interactions available in Geant4-DNA. The influence of sub-excitation processes and electron tracking cut is discussed. Results are compared to literature data when available. As an example, a simple calculation of the relative biological effectiveness (RBE) in the context of the Theory of Dual Radiation Action using the present proximity functions yields up to a factor of 2 variation of the electron RBE in the energy range from 100 eV to 100 keV.

Ionizing Radiation and Complex DNA Damage: Quantifying the Radiobiological Damage Using Monte Carlo Simulations

“…This functionality has provided a unique theoretical tool for investigating differences between sparse (or low linear energy transfer (LET)) and dense (or high-LET) ionization radiations at the nanometer level, which is not possible by other means [32]. MCTS codes have been the workhorse of theoretical microdosimetry, enabling systematic calculations of lineal energy spectra (the stochastic analog of LET), proximity functions, ionization cluster distributions, etc., which are used for explaining and predicting the quality factor or the relative biological effectiveness of different ionizing radiations [33][34][35][36][37][38][39]. In addition, quantitative estimates of the early "direct" DNA damage can be obtained by combining the spatial distribution of energy-transfer points (above a certain threshold) with the geometric structure of DNA [40][41][42][43][44][45].…”

Modeling of yield estimation for DNA strand breaks based on Monte Carlo simulations of electron track structure in liquid water

“…[1][2][3] A Monte Carlo code for the track structure simulation at the nanometer scale in liquid water [4][5][6] is a powerful tool for the mechanistic investigation of the DNA damage induction. 7,8 Most of the energy deposition by the ionizing radiation is composed of secondary electrons, 5 thus a reliable code for predicting the track structure of electrons is required for computing the spatial distribution of DNA hits. However, radiation transport qualities in the low energy range below sub-kiloelectron volt remain uncertain.…”

IDDRRA: A novel platform, based on Geant4‐DNA to quantify DNA damage by ionizing radiation

“…Any new updates on the Physics lists by the Geant4-DNA community will be incorporated in IDDRRA tool updates, as soon as they are available in the field. [30][31][32] One consideration is that in their current form, the physics lists treat every structure as water. Thus, whereas all structures have a robust geometrical model, their chemical composition is approximated as being water equivalent.…”