Monte Carlo simulations of energy deposition and DNA damage using TOPAS-nBio

Abstract

Purpose. Monte Carlo (MC) track structure codes are commonly used for predicting energy deposition and radiation-induced DNA damage at the nanometer scale. Various simulation parameters such as physics model, DNA model, and direct damage threshold have been developed. The differences in adopted parameters lead to disparity in calculation results, which requires quantitative evaluation. Methods. Three simulation configurations were implemented in TOPAS-nBio MC toolkit to investigate the impact of physics models, DNA model, and direct damage threshold on the prediction of energy deposition and DNA damage. Dose point kernels (DPKs) of electrons and nanometer-sized volumes irradiated with electrons, protons, and alpha particles were utilized to evaluate the impact of physics models on energy deposition. Proton irradiation of plasmid DNA was used to investigate the disparity in single-strand break and double-strand break (DSB) yields caused by differences in physics models, DNA models, and direct damage thresholds. Results. Electron DPKs obtained with different physics models show similar trends but different diffusiveness and maximums. Energy deposition distributions in nanometer-sized volumes irradiated with electrons, protons, and alpha particles calculated using different physics models have the same trend although discrepancies can be observed at the lowest and highest energy deposits. Strand breaks from incident protons in DNA plasmids vary with adopted parameters. For the configurations in this study, changing physics model, DNA model, and direct damage threshold can cause differences of up to 57%, 69%, and 15% in DSB yields, respectively. All these simulation results are essentially in agreement with previously published simulation or experimental studies. Conclusion. All the physics models, DNA models, and direct damage thresholds investigated in this study are applicable to predict energy deposition and DNA damage. Although the choice of parameters can lead to disparity in simulation results, which serves as a reference for future studies.

Monte Carlo study of TG‐43 dosimetry parameters of GammaMed Plus high dose rate 192Ir brachytherapy source using TOPAS

“…MC calculated TG‐43 dosimetry parameters using new configurations were carried out in this study and compared with previously published data, thus validated the proposed MC model and provided a new TG‐43 dataset. Implemented in TOPAS, an easier‐to‐use application of Geant4 MC code for the medical physicist, this model can be easily utilized in further studies regarding MC calculations such as IMBT and microdosimetric studies (along with the TOPAS‐nBio extension) 29,30 …”

“…In this study, the TG-43 dosimetry parameters for Varian Gam- microdosimetric studies (along with the TOPAS-nBio extension). 29,30 The deviation between calculations could be attributed to different source spectra and cross sections. A previous research 31 indicated that different 192 Ir source spectra can cause S k differences up to 2%.…”

Contemporary biomedical engineering perspective on volitional evolution for human radiotolerance enhancement beyond low-earth orbit

“…Although probabilistic scenarios may be estimated for an individual’s radiation exposure on a mission (for example, with Monte Carlo methodology), true physiological consequences remain ultimately unknown, especially combined with other effects from phenomena like microgravity and isolated environments ( 143 ). Without a comprehensive understanding of the phenotypic response of Homo sapiens to space radiation, a genotypic solution may misidentify or omit essential or corollary transcription pathways.…”

Estimation of the relative biological effectiveness for double strand break induction of clinical kilovoltage beams using Monte Carlo simulations

“…The ionization energy of liquid water was set at 12.6 eV 20 and any interaction depositing energy equal to or greater than that value was assumed to cause ionization, with any excess energy transferred to the free radicals as kinetic energy. The DNA damage threshold was taken as 17.5 eV 21 and if a free radical kinetic energy was greater than or equal to this value, an indirect SSB was assumed. If any two indirect SSB occurred within 3.4 nm of each other (the average separation of 10 DNA base pairs) this was classified as an indirect DSB 22 .…”