Human Cytogenetic Dosimetry

Abstract

Cytogenetic dosimetry estimates to guide treatment of persons internally contaminated with transuranic elements were not previously 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 for 241Am .alpha. particle (5.49 and 5.44 MeV) radiation of Go lymphocytes was generated. Cells were exposed to 43.8, 87.7, 175.3 or 350.6 nCi/ml 241Am for 1.7 h giving doses of 0.85, 1.71, 3.42 or 6.84 rad. Based on dicentric chromosome yield, an equation describing the linear dose-response rate (Y = 4.90(.+-. 0.42) .times. 10-2 X, where Y = dicentrics per cell, X = dose in rads) was derived. The 2-break asymmetrical exchanges in cells damaged by .alpha. particle radiation are overdispersed when compared to a Poisson distribution. An example shows 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 [relative biological effectiveness] value of 118 at 0.85 rad is calculated for the efficiency of 241Am .alpha. particle induction of dicentric chromosomes in human Go lymphocytes as compared with the efficiency of 60Co .gamma. radiation. The maximum theoretical value for the RBE for cytogenetic damage from .alpha. irradiation was 278 at 0.1 rad or less which is in marked contrast to previously reported RBE values of .apprx. 20.