A method of calculating initial DNA strand breakage following the decay of incorporated 125I.

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.