HUMAN CYTOGENETIC DOSIMETRY - DOSE-RESPONSE RELATIONSHIP FOR ALPHA-PARTICLE RADIATION FROM AM-241

Cytogenetic dosimetry estimates to guide treatment of persons internally contaminated with transuranic elements have not previously been possible because appropriate in vitro dose-response curves specifically for alpha particle irradiation of human lymphocytes do not exist. Using well-controlled cytogenetic methods for human lymphocyte culture, an experimentally derived dose-response curve for241Am alpha particle (5.49 and 5.44 MeV) radiation of G0lymphocytes was generated. Cells were exposed to 43.8, 87.7, 175.3 or 350.6 nCi/ml241Am for 1.7 hr giving doses of 0.85, 1.71, 3.42 or 6.84 rad. Based on dicentric chromosome yield, the linear dose-response equation is Y = 4.90(±0.42) x 10-2X, with Y given as dicentrics per cell and X as dose in rads. The study also shows that the two-break asymmetrical exchanges in cells damaged by alpha particle radiation are overdispersed when compared to a Poisson distribution. An example is presented to show how the derived dose-response equation can be used to estimate the radiation dose for a person internally contaminated with an actinide. An experimentally derived RBE value of 118 at 0.85 rad is calculated for the efficiency of241Am alpha particle induction of dicentric chromosomes in human G0lymphocytes as compared with the efficiency of60Co gamma radiation. The maximum theoretical value for the RBE for cytogenetic damage from alpha irradiation was determined to be 278 at 0.1 rad or less which is in marked contrast to previously reported RBE values of approx. 20. © 1979 Health Physics Society.