Comet assay to sense neutron 'fingerprint'

The suitability of comet assay to identify DNA damage induced by neutrons o f varying energy was tested. For this purpose, monoenergetic neutrons from Hiroshima University Radiobiological Research Accelerator (HIRRAC) were use d to induce DNA damage in irradiated human peripheral blood lymphocytes. Th e level of damage was computed as tail moment for different doses (0.125-1 Gy) and compared with the effects resulting from irradiation with Co-60 gam ma. The neutron-irradiated cells exhibited longer comet tails consisting of tiny pieces of broken DNA in contrast to the streaking tails generated by 60Co gamma. The peak biological effectiveness occurred at 0.37 and 0.57 MeV ; a further increase or decrease in neutron energy led to a reduced RBE val ue. The RBE values, as measured by the comet assay, were 6.3, 5.4, 4.7, 4.3 , 2.6, and 1.7 for 0.37, 0.57, 0.79, 0.186, 1, and 2.3 MeV neutrons. The lo wer RBE value obtained by the comet assay when compared to that for other b iological end points is discussed. This study reports the usefulness of the alkaline comet assay for identifying DNA damage induced by neutrons of the same radiation weighting factor. The comet assay is a potential tool for u se in neutron therapy, as well as a method for the rapid screening of sampl es from individuals accidentally exposed to radiation. (C) 2000 Elsevier Sc ience B.V. All rights reserved.