In vitro dose-response curves of unstable chromosome aberrations in human lymphocytes have been obtained for 250 kV X-rays and cobalt-60γradiation. The aberration yields have been fitted to the quadratic function Y = αD + βD2, which is consistent with the single-track and two-track model for aberration formation. The values of the coefficients α and β support the hypothesis that the dose-rate effect is limited to the D2 term. The main difference between the coefficients for X- and γradiation is in the α values, indicating that X-rays are slightly more efficient, at lower doses, in producing two lesions with a single ionizing track. The lower limits of dose estimate, with 500 cells analysed, are 4 rad for X-rays and 10 rad γradiation. Further evidence is presented confirming that, for cytogenetic dosimetry, in vitro dose-response curves should be prepared by irradiating whole blood maintained at 37°C and prior to PHA stimulation. Curves were plotted showing the variation of the number of cells without aberrations with radiation dose and the shape of these curves were compared with those from human cell survival experiments.
Bibliographical noteFunding Information:
Medical Research Council, Radiobiology Unit, Harwell, Didcot, Oxon . OX11 ORD, U .K .