@misc{oai:repo.qst.go.jp:00079014, author = {Sakata, Dousatsu and Sakata, Dousatsu}, month = {Feb}, note = {Introduction: Monte Carlo (MC) mechanistic simulations are a promising tool for the modeling of early DNA damage induction by ionizing radiation. They allow to simulate not only physical interactions but also chemical processes in combination with sim- plified geometries of biological targets for the prediction of such damage. In the last decades, several MC codes were developed to predict DNA damage, like KURBUC PARTRAC and Geant4-DNA. Recently, Geant4-DNA has demonstrated the possibility to evaluate early DNA damage in an E. coli bacterium and in a fibroblast cell nucleus irradiated by protons [4]. We have presented for the first time the combination of such features (physics, chemistry and biological geometry) in a single Geant4-DNA application for the modelling of early DNA damage induction in a cell nucleus [5]. In this talk, we present progress of the modelling in Geant4-DNA of biological DNA damage. Material and Methods: As used in the previous work, we built fractal based cell nucleus geometry composed by double-helix DNA fiber and histone. We simulated physical particle transportation followed by radiolysis chemical product productions, diffusion of free radicals and chemical reactions in gamma and proton radiation fields. Early DNA damage is calculated as either direct damage or indirect damage. Then the damage clusters are classified according to the damage type definition proposed by Nikjoo. Results: In this talk, mainly DSB yields and fraction of indirect damage and biological repair will be presented. For instance, the simulated repair prediction shows a good agreement with experimental data. Conclusion: We have developed for the first time a Monte Carlo simulation based on Geant4-DNA that calculates not only early DNA damage but also late DNA damage prediction such as foci accumulation like γH2AX., Mini- Micro- Nano- Dosimetry (MMND)-Innovative Technologies in Radiation Oncology (ITRO) 2020}, title = {Evaluation of ionizing radiation induced DNA damage on a cell nucleus by integrated track structure Monte Carlo simulations using Geant4-DNA}, year = {2020} }