The Lethality of Radiation-Induced DNA Double-Strand Breaks for Radiations of Differing LET

Abstract

Using the filter elution technique it is possible to measure DNA double-strand breaks (dsb) in the same dose range as cell survival measurements. Unlike other techniques for measuring dsb, the dose-effect relationship for dsb induction with low LET radiation is non-linear with dose. The shape of the induction curve mirrors that of the cell survival curve such that a plot of lethal lesions (-ln[surviving fraction]) versus dsb produces a linear relationship (Radford, 1985). We have repeated these measurements for radiations of differing linear energy transfer (LET) and for breaks induced chemically by H₂O₂ treatment. The yield of DNA dsb and cell survival in Chinese hamster V79 cells were measured after irradiation at 4°C by 400 keV electrons, 250 kVp X-rays, 1.90 MeV, 1.15 MeV, 0.76 MeV protons, 2.3 MeV neutrons and 3.8 MeV ²³⁸Pu α-particles. For H₂O₂ treatment, cells were incubated with the drug (10^–5–10^–2M) for 20 minutes also at 4°C. Depending on the source used, cells were irradiated in suspension (X-rays and neutrons), attached on 13mm diameter Thermanox coverslips (electrons) or collected onto polyvinylidine difluoride membrane filters (protons, α-particles and H₂O₂). Immediately after irradiation, cells were assayed for DNA dsb using the filter elution technique (pH9.6) or assayed for their colony-forming ability.