A New DNA Target Model for Track Structure Calculations and Its First Application to I-125 Auger Electrons

Abstract

A DNA target model has been developed, based on the geometrical co-ordinates of individual atoms. This model is used to analyse DNA damage produced by Auger electron tracks from the decay of 125I. The high resolution of this target model enables the distinction between direct and indirect electron hits, i.e. hits inside the atomic volumes of the DNA molecule and those hitting the water molecules assumed in the space between the atomic volumes. Three types of calculations have been performed: (1) the evaluation of the energy deposition in the surroundings of the decaying 125I nuclide demonstrating different fractions of direct to indirect hits at different parts of the DNA molecule (phosphate/sugar strand or bases), (2) a detailed energy deposition pattern in the radiolabelled base, indicating that this most burdened molecule is not necessarily destroyed by direct hits, and (3) a calculation of single- and double- strand breaks by using different threshold values for effective direct and indirect hits, resulting in a good correlation with experimental data on strand break efficiency.

Site- and energy-selective slow-electron production through intermolecular Coulombic decay

“…The damage is thought to arise primarily from two sources. The Auger cascade initiated in the high-Z element either spontaneously (in radionuclides) or by absorbing an X-ray photon leads to the emission of genotoxic Auger electrons with energies below 500 eV [34]. Following this cascade, electron transfer to the highly charged high-Z ion from the environment may also result in a Coulomb explosion causing further damage [35].…”

Modelling of Initial Events and Chemical Behaviour of Species Induced in DNA Units by Auger Electrons from125I,123I and Carbon

“…The track structure code used in this work (9) has been continuously improved, e.g., by introducing active DNA sites and, furthermore, the linear DNA plasmid target structure (8) has been developed to a nucleosome model to be closer to cellular DNA conditions. All calculated numbers of single strand breaks (ssb) and double strand breaks (dsb) as well as the spatial distribution of ssb in linear DNA show reasonable values when compared with experimental data (10).…”

“…track structures and target models allowed to trace the fate of single electrons in spatial relation to critical biological structures. Strand break induction had been simulated (7) and by introducing a target model with atomic resolution (8) the distinction between direct and indirect effects in the simulation became possible.…”

Review of Geant4-DNA applications for micro and nanoscale simulations

“…For the first time with Geant4-DNA, they also included a method using a liquid water virtual cylinder around the DNA for the recording of indirect effects, initially proposed by Pomplun [58] and using prototype radiolysis simulation capabilities available in Geant4-DNA. The authors demonstrated the reasonable agreement on the number of strand breaks per radionuclide decay between Geant4-DNA and theoretical and experimental works from the literature, underlining the applicability of Geant4-DNA for nanodosimetry.…”