Frequencies of chromosomal aberrations induced in human blood lymphocytes by low doses of X-rays

The dose-response for radiation-induced chromosome aberrations in human lymphocytes is usually fitted to the quadratic model. This assumes that slope is essentially linear at low doses. Empirical observations of linearity at < 200 mGy are sparse. Some data have been published indicating a non-linear (threshold) response and are reviewed. One X-rays study showed a plateau in response up to 50 mGy, with a significant dip below control level at 4 mGy. The mechanism proposed to explain non-linearity is that low doses stimulate the enzymic repair capability of lymphocytes. Preliminary data are presented from an experiment by six laboratories in which the low dose-response for X-rays has been re-examined. The plateau in the dose-response relationship does not extend to doses above ∼ 10 mGy. No irradiated cells yielded aberration levels significantly below the control. Over the range 0-300 mGy response can be fitted to a linear regression. There are variations in sensitivity between cells from different donors. Some lymphocytes contained > 1 exchange aberrations. This may indicate a small subset of cells especially susceptible to induction of aberrations by low doses. (author)