The Irradiation of V79 Mammalian Cells by Protons with Energies below 2 MeV. Part II. Measurement of Oxygen Enhancement Ratios and DNA Damage

Summary

The effectiveness of low-energy (below 2 MeV) protons at inducing DNA damage in the form of single- and double-strand breaks has been determined. Protons with mean energies of 1·90 MeV, 1·15 MeV and 0·76 MeV corresponding to track average LETs of 17 keV/μm, 24 keV/μm and 32 keV/μm, respectively, have been used and compared with 250 kVp X-rays and 3·8 MeV ²³⁸Pu α-particles. Although there was variation in the RBE for DNA ssb induction with LET, the RBEs for dsb induction at all three proton energies and for 3·8 MeV α-particles were all around 1·0. This suggests that, if DNA dsb are important in radiation-induced cell lethality, the probability of an induced dsb leading to a lethal event increases with increasing LET of radiation. Oxygen enhancement ratios were measured for both cell survival and DNA dsb induction, and in both cases a decrease in OER with increasing LET was observed.