A Method of Calculating Initial DNA Strand Breakage Following the Decay of Incorporated¹²⁵I

Abstract

Two sources of individual Auger electron spectra and an electron track code were used with a simple model of the DNA to successfully simulate the single-strand DNA breakage measured by Martin and Haseltine (1981). The conditions of the calculation were then extended to examine patterns of single-strand breaks in both strands of the DNA duplex to score double-strand breaks. The occurrences of five types of break were scored. The total number of double-strand breaks (dsb) per decay at the site of the decay was 0.90 and 0.65 for the different Auger electron spectra. It was shown that for mammalian cells an additional source of double-strand breaks from low LET radiation added approximately 0.17 dsb/decay to each, giving a final total of 1.07 and 0.85 dsb/decay for mammalian cells depending on the electron spectrum. Further is is shown that the energy deposition in the DNA from the iodine decay is very complex, with a broad range of energy depositions and products. Even for a particular energy deposited in the DNA different types of strand break are produced. These are identified and their probabilities calculated.

Review of Geant4-DNA applications for micro and nanoscale simulations

“…The first study investigated the influence of DNA conformation of strand break yields [55]. The three B-, A-and Z-DNA conformations were studied for 34 bp segments of DNA, including the B-DNA description based on the earlier work by Charlton and Humm [59]. They also took into account a liquid water hydration shell around the DNA for the recording of both direct and indirect effects.…”

“…They used the Charlton and Humm model [59] for the calculation of direct and indirect damage, for a total of about 10 6 bp. They obtained predictions similar to theoretical and experimental works demonstrating the efficiency of this simple approach.…”

“…A last study based on a similar geometrical approach has been proposed by Li et al [60]: the geometrical model by Charlton and Humm [59] has been used in combination with six different sets of inelastic cross section data describing the transport of electrons and calculated by the authors. These data were imported into their own Geant4-DNA application.…”

“…In parallel, Xie et al [64] compared estimations obtained using the previously described cylinder volume approach (model from Charlton and Humm [59]) with an atomistic model created from published DNA atomic coordinates; they also studied the effect of doubling Van der Waals radii in the atomistic model in order to take into account DNA hydration shell. In their results, the authors extracted simple and complex damage yields and demonstrated that the yields obtained with the cylinder volume approach were the highest.…”

A computer-generated supercoiled model of the pUC19 plasmid

“…Furthermore, each cylinder was sliced into 80 discs representing the base pairs. The first linear DNA model which allowed a differentiation between base and sugar-phosphate volumes was created by the same author (Charlton and Humm 1988). A solid straight cylinder with a diameter of 2.3 nm was divided into three compartments: an inner cylinder of 1.0 nm diameter along the central axis is occupied by the bases.…”