Efficacy of Radiation Countermeasures Depends on Radiation Quality

The detonation of a nuclear weapon or a nuclear accident represent possible events with significant exposure to mixed neutron/gamma-radiation fields. Although radiation countermeasures generally have been studied in subjects exposed to pure photons (gamma or X rays), the mechanisms of injury of these low linear energy transfer (LET) radiations are different from those of high-LET radiation such as neutrons, and these differences may affect countermeasure efficacy. We compared 30-day survival in mice after varying doses of pure gamma and mixed neutron/gamma (mixed field) radiation (MF, Dn/Dt = 0.65), and also examined peripheral blood cells, bone marrow cell reconstitution, and cytokine expression. Mixed-field-irradiated mice displayed prolonged defects in T-cell populations compared to mice irradiated with pure gamma photons. In mouse survival assays, the growth factor granulocyte colony-stimulating factor (G-CSF) was effective as a (post-irradiation) mitigator against both gamma-photons and mixed-field radiation, while the thrombopoietin (TPO) mimetic ALXN4100TPO was effective only against gamma irradiation. The results indicate that radiation countermeasures should be tested against radiation qualities appropriate for specific scenarios before inclusion in response plans. (C) 2012 by Radiation Research Society