Source-linked AI summary
The Geant4-DNA project
S. Incerti, G. Baldacchino, M. Bernal, R. Capra, C. Champion, Z. Francis, S. Guatelli, P. Gueye, A. Mantero, B. Mascialino, P. Moretto, P. Nieminen, A. Rosenfeld, C. Villagrasa, C. Zacharatou
TL;DR
Geant4-DNA targets the need for validated simulation of radiation-induced biological damage at cellular and sub-cellular scales. It extends Geant4 with discrete particle-interaction processes and models, alongside detailed DNA geometries, to support simulations of direct DNA damage. The project presents available physics developments and identifies validation, geometrical refinement, and broader physics coverage as next steps.
Problem
Understanding and simulating ionising-radiation effects at cellular and sub-cellular scales remains challenging, while validated tools are important for radioprotection.
Method
Geant4-DNA extends the open-source Geant4 Monte Carlo toolkit with discrete, step-by-step physical-interaction processes and complementary or alternative model classes.
Results
The paper presents available Geant4-DNA physics processes and models and expects detailed DNA geometries to enable simulations of direct single- and double-strand breaks.
Takeaways & Limitations
Validated predictions will be compared with single-ion microbeam experiments, supporting potential applications in radioprotection, space radiation, microdosimetry, and radiotherapy.
Takeaways & Limitations
Quantitative conclusions about DNA single- and double-strand-break estimates require finer geometrical models and higher-statistics simulations.
Abstract
from arXiv · showhide
The Geant4-DNA project proposes to develop an open-source simulation software based and fully included in the general-purpose Geant4 Monte Carlo simulation toolkit. The main objective of this software is to simulate biological damages induced by ionising radiation at the cellular and sub-cellular scale. This project was originally initiated by the European Space Agency for the prediction of deleterious effects of radiation that may affect astronauts during future long duration space exploration missions. In this paper, the Geant4-DNA collaboration presents an overview of the whole ongoing project, including its most recent developments already available in the last Geant4 public release (9.3 BETA), as well as an illustration example simulating the direct irradiation of a chromatin fibre. Expected extensions involving several research domains, such as particle physics, chemistry and cellular and molecular biology, within a fully interdiciplinary activity of the Geant4 collaboration are also discussed.
1 Introduction
Geant4-DNA addresses the challenge of simulating ionising-radiation effects at cellular and sub-cellular scales, where validated tools are important for radioprotection and biological research. It extends the open-source Geant4 Monte Carlo toolkit through interdisciplinary development rather than creating a separate biological-damage code.
- Validated simulation tools are important for studying ionising-radiation effects at cellular and sub-cellular scales, particularly for human radioprotection.
- Geant4-DNA proposes an experimentally validated platform for modelling DNA damage induced by ionising radiation.
- The project combines expertise in particle physics, chemistry, biophysics, molecular and cellular biology, and computer science.
- Monte Carlo simulation uses random number generators to reproduce the stochastic nature of particle–matter interactions, although complex simulations may require substantial computing power.
- The project extends the general-purpose, open-source Geant4 Monte Carlo toolkit with capabilities for microdosimetry and biological-damage simulation.
- Geant4-DNA began at the European Space Agency in 2001, with early liquid-water microdosimetry processes delivered into Geant4 in December 2007.
2 The Geant4-DNA physics processes and models
Geant4-DNA provides discrete, step-by-step simulation of light-particle interactions in liquid water, with models spanning electrons, protons, hydrogen, helium, and charged helium states. The release includes cross-section models, nanometer-scale track visualizations, and user controls for energy limits and step sizes.
- Available physics processes and models: Geant4-DNA models electron, proton, hydrogen, helium, and charged-helium interactions in liquid water using purely discrete, step-by-step tracking.Process classes compute interaction cross sections and describe products, kinematics, secondary particles, and energy deposits.
- Available physics processes and models: The Geant4-DNA process and model classes were redesigned for Geant4 9.3 BETA, adding features such as direct access to cross-section values at a given energy.The redesign adopted a coherent approach across Geant4 electromagnetic interactions.
- Available physics processes and models: The extension includes elastic scattering, ionisation, excitation, and charge-changing processes across particle-specific energy ranges, with applicability listed in Table 1.Excitation and charge increase/decrease are specific to Geant4-DNA and are absent from Geant4 Standard and Low Energy electromagnetic packages.
- Available physics processes and models: Below 100 eV, electron elastic scattering dominates; at higher energies, elastic scattering and ionisation dominate in the reported 8.23 eV–30 keV range.The electron models include Screened Rutherford and Champion elastic-scattering models, alongside ionisation and excitation models.
- Available physics processes and models: For protons, charge decrease dominates at low energy, while hydrogen ionisation dominates throughout its reported energy range.The figures plot proton and hydrogen process cross sections from 100 eV to 10 MeV.
- Track structure modelling: A 1 keV electron track is resolved in liquid water by tracking primary and secondary electrons to 8.23 eV, with each elastic scattering, excitation, and ionisation interaction represented.Below 8.23 eV, electrons stop and deposit their energy locally; users can also impose volume-specific maximum step sizes with G4StepLimiter.
3 Modelling direct radiation damages to DNA
Geant4-DNA combines detailed biological geometries with particle tracking to model direct radiation damage in DNA, from cellular structures to atomistic chromatin models. A 500 keV He+ example illustrates how simulated energy deposits can be converted into strand-break estimates, although higher granularity and statistics are needed before quantitative validation.
- 3 Modelling direct radiation damages to DNA: Geant4-DNA integrates with Geant4 geometry tools to represent biological targets at sub-micrometre resolution using voxellized or atomistic approaches.The integration supports detailed particle tracking within these geometries.
- 3.2 An atomistic DNA geometrical model: The atomistic model represents DNA at nanometre scale through four levels: deoxynucleotide pairs, the DNA double helix, nucleosomes, and the chromatin fibre.Its dimensions and positions follow the B-DNA molecular configuration.
- 3.2 An atomistic DNA geometrical model: A chromatin fibre is built from repeated slices of 6 nucleosomes, with a 10-slice example measuring about 100 nm long, 30 nm in diameter, and containing 1.2×10^4 base pairs.The model volumes are filled with liquid water, matching the domain of the Geant4-DNA processes.
- 3.2 An atomistic DNA geometrical model: Geant4 tracks particles through the model with a 0.1 nm user step limit, allowing individual energy deposits to be located and DNA bases to be identified by their structural positions.Geometrical symmetries support top-to-bottom implementation without explicitly defining every deoxynucleotide pair.
- 3.2 An atomistic DNA geometrical model: Using a 10.79 eV energy-deposit threshold for SSBs and a spacing rule for DSBs, one 500 keV He+ particle could generate 9 SSBs and 2 DSBs in the fibre model.A DSB requires two SSBs on opposite strands separated by no more than 10 base pairs.
- 3.2 An atomistic DNA geometrical model: The authors caution that the geometry needs finer granularity and higher-statistics simulations before quantitative conclusions about strand-break validity can be drawn.They nevertheless present the combined approach as promising for nanometre-scale modelling.
4 Modelling chemistry with Geant4-DNA
The project addresses direct DNA damage while extending Geant4 toward chemical-stage modelling. Reactive radical species and their interactions were still being implemented, so this capability remained under development.
- 4 Modelling chemistry with Geant4-DNA: Direct ionising-radiation damage can transfer sufficient energy to DNA to generate strand breaks, but it is not dominant for low-LET radiation.The direct-damage stage occurs between cellular penetration and about 10^-15 s after irradiation.
- 4 Modelling chemistry with Geant4-DNA: Geant4 could model particle interactions with matter, but not interactions between particles such as collective effects.This limitation motivated work on reactive radical species.
- 4 Modelling chemistry with Geant4-DNA: Reactive radical species and their interactions were planned as new Geant4 classes to add chemical-stage functionality.Their implementation was described as currently in progress.
5 The microdosimetry example for Geant4 users
The microdosimetry advanced example shows users how to configure Geant4-DNA physics lists within Geant4’s redesigned electromagnetic-process framework.
- 5 The microdosimetry example for Geant4 users: The microdosimetry advanced example adapts its physics list to Geant4-DNA’s redesigned processes and models in version 9.3 BETA.It demonstrates specifying the particles and processes available through the Geant4-DNA physics list.
6 Geant4 for VMware™
Geant4-DNA was distributed as part of Geant4’s low-energy electromagnetic package, with a ready-to-use virtualized software suite intended to ease installation for novice users.
- 6 Geant4 for VMware™: All Geant4-DNA processes and models were accessible in Geant4, alongside a free Windows™ or Macintosh™ VMware™ suite containing the complete toolkit and examples.The suite emulates a Scientific Linux™ machine after download.
7 Conclusion and perspectives
Geant4-DNA is being extended into an integrated platform for simulating radiation-induced DNA damage across physical, chemical, and biological scales. The project emphasizes high-resolution modelling, experimental validation, and future application in radioprotection and radiotherapy.
- Current platform: Geant4-DNA extends Geant4 with sub-micrometer particle-interaction modelling and detailed DNA geometries to simulate direct SSBs and DSBs.The project combines physical processes with preliminary molecular-scale DNA models.
- Future physics: Additional physics models are planned for photons, carbon and oxygen ions, biological materials, and energies down to 0.025 eV.Planned additions include vibrational excitation models and extended energy ranges.
- Future chemistry: Chemistry modelling is planned to represent oxidative radicals, their diffusion, and interactions, enabling simulation of non-direct DNA damage.
- Limitations and validation: High-resolution molecular geometries remain an open requirement, and DNA models need greater granularity and higher statistics before quantitative strand-break conclusions are drawn.The authors specifically identify atomic descriptions of phosphodiester groups as a possible refinement.
- Limitations and validation: Predictions will be compared with dedicated single-ion microbeam experiments and other simulation codes to validate DNA-damage modelling.Single-cell irradiation facilities can precisely quantify SSBs and DSBs after irradiation.
- Applications: As an open-source Geant4 component, the platform is intended for transparent use in radioprotection, space-radiation studies, microdosimetry, and radiotherapy.