The effect of changes in dose rate on the yield of chromosome aberrations in human lymphocytes exposed to gamma radiation

Abstract

The yield of chromosome aberrations was studied in G 0 human peripheral blood lymphocytes following in vitro exposure to 100, 250 and 500 rad caesium-137 gamma radiation. The doses were given at various rates up to 400 rad per h with the longest exposures lasting for approx. 50 h. At 500 and 250 rad the dicentric yields fell by 66 and 64% when the dose rate was reduced from 400 to 40 rad per h whereas at 100 rad the reduction was only 29%. Reductions were also noted in the frequency of acentric aberrations. At the higher dose rates (>150 R/h) the aberration yield was constant and agreed with data published elsewhere for 3000 R/h. The dose rate at which the decline in aberration yield became apparent was dose dependent and, for dicentrics, occurred at about 150, 100 and 25 rad/h respectively for the 500-, 250- and 100-rad doses. The data are interpreted in terms of the quadratic model of aberration induction in which the dose-squared term represents dose rate dependent two-track aberrations which constitute an increasingly important component of yield as dose increases. The implications of this work for cytogenetic dosimetry are discussed.