Radiation-induced chromosomal aberrations in human lymphocytes. I. Dependence on the dose of gamma-rays and an anomaly at low doses.

Cultures of human lymphocytes obtained from blood of healthy adult donors were irradiated with different doses of 60Co gamma-rays and the irradiated cells were analysed in metaphase 50 h after irradiation. The effect (total yield of aberrations of chromosome type, or total yield of exchange type aberrations) produced by the lowest dose (5 rad) appears to be statistically significant in a sample of 1500 cells. In the usual dose range (25-400 rad), both parabolic and linear-quadratic equations give a satisfactory fit of experimental data (dicetrics, fragments, or all aberrations of chromosome type). Low doses of gamma-rays, however, produced more aberrations than expected, if one extrapolates dose-effect curves from higher doses. Both relations should be considered, therefore, merely as empirical equations. Dicentrics show at low doses (10-30 rad) a plateau which appears to be statistically significant. Some indications are obtained that the total number of chromosome-type aberrations is a more reliable criterion of cytogenetic damage than the usually accepted yield of dicentrics and rings.