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

The yield of chromosome aberrations was studied in Go human peripheral blood lymphocytes following in vitro exposure to 100, 250 and 500 rad of 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 10 rad per h whereas at 100 rad the reduction was only 29%. Reductions were also noted in frequency of acentric aberrations. At the higher dose rates (greater than 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.