Algorithms for the evaluation of radiation induced chromosome aberration yields per cell from flow karyotypes

CHO-K1 cells were irradiated in G0/G1-phase with 150 kV X-rays. Single chromosomes isolated from metaphase cells and stained with DNA intercalating dye DAPI were analyzed in the ICP 22 with a modified flow chamber. In order to study dose-dependent changes in the flow karyotypes, they were split into peak- and background-portions by an iterative fit algorithm. As in a first approach, estimates of the frequencies of chromosome lesions were derived from an evaluation of the dose-dependent reduction in peak contents. The number of radiation-induced lesions per chromosome was found to be proportional to its length. As a second approach, the number of fluorescence events in the histogram background was corrected for non-chromosomal debris and evaluated interms of chromosome aberration frequency per cell, which was consistent with the yields of dicentric chromosomes and acentric fragments observed in microscopic investigations. As a third approach, lesion frequencies were calculated from the corrected background light sum in the karyotypes, utilizing a Monte Carlo model to simulate the effect of aberration formation on the flow histogram. The results indicate that the number of chromosome lesions observed by flow cytometry can be quantitatively related to the yield of structural chromosome aberrations detected by microscopic analysis. Dose-effect relations and split-dose kinetics are given as examples demonstrating the usefulness of this technique in radiobiology. Time saving compared to microscopic analysis was of the order of 90%.