Analysis of chromosome aberrations in human peripheral lymphocytes induced by in vitro alpha-particle irradiation

Irradiation of human lymphocytes by alpha-particles under different conditions has been seen to be substantially more effective in the induction of dicentric chromosomes than irradiation by gamma-rays. However, the relative biological effectiveness (RBE) determined in these studies differed by a factor of more than 10. These variations in RBE are likely to be due in part to differing exposure conditions. Therefore, a technique designed to insure uniformity of irradiation was developed in the present study, and complications due to the cell cycle kinetics were controlled. After stimulation with phytohaemaglutinin (PHA), separated lymphocytes were allowed to attach for 3 h to the thin foil bottom of an irradiation chamber. Cell monolayers were exposed with alpha-particles from Am-241. Strong over-dispersion was noted for the cell-to-cell variance of the number of dicentrics, The dose response of dicentrics was linear, with a yield of 0.27 dicentrics per cell and per Gy. This corresponds to a low dose RBE of 15 relative to Cs-137 gamma-ray exposure under the same experimental conditions.