Dosimetry and risk from low- versus high-LET radiation of Auger events and the role of nuclide carriers

Purpose: To analyse the lethality to mammalian cells of 125I-decays in DNA, in antipyrine in the whole cell and in oligodeoxynucleotides in the nucleus outside DNA as a function of Auger event-site and number. Materials and methods: Auger events cause both low- and high-linear energy transfer energy depositions including charge neutralization at the daughter nuclide. Microdosimetry allows the expression of absorbed dose to a defined micromass and the number of such events at given sites. Published data were used to relate micromass dose and event number to the dose to reduce survival to 37% of the initial survival (D37). Results: The D37 of 125I-decays in DNA was 0.1 Gy in terms of absorbed dose to the cell nucleus and about 30 in terms of average decays per nucleus or whole cell. The D37 of 125I-decays in antipyrine was 1.5 Gy for absorbed dose to the cell nucleus, about 250 in terms of average decays per nucleus and about 2×103 for average decays per whole cell. 125I-decays in oligodeoxynucleotides were much less toxic than 125I-decays in antipyrine by a factor of about 25 in terms of average absorbed dose to the cell nucleus, by a factor or about 40 in terms of average decays per cell nucleus and by a factor of six in terms of average decays per whole cell. Conclusion: The unexpected low toxicity of 125I-decays in nuclear oligodeoxynucleotides outside the DNA in comparison with 125I-decays in antipyrine in the nucleus or the whole cell demands further attention on the role of oligodeoxynucleotides in altering cellular radiation sensitivity.