Quantitative analysis of the chromosome damage at first division of human lymphocytes after60CO?-Irradiation

Abstract

Chromosome analyses in human peripheral lymphocytes provide a means of estimating equivalent whole-body doses after actual or suspected over-exposure to ionizing radiations [2,7,10,14]. As a prerequisite representative calibration curves have to be established from standardized in vitro experiments.For an adequate consideration of cell proliferation kinetics on aberration yield, chromosome analyses should be carried out on cultures treated with 5-bromodeoxyuridine (BrdU) in only first-division cells (M1) , identified by fluorescence plus Giemsa staining (FPG) [8,19].For experiments with 220-keV X-rays [23] and 14.5-MeV neutrons [6] we could recently demonstrate that distinct different dose-effect curves for dicentrics and acentrics may result depending on the application of FPG-staining or conventional staining.Additionally, for calibration purposes an appropriate statistical analysis of dose-response functions must be Carried out. For an estimation of regression parameters of common models of dose-response mainly the least squares method is used. Since the variances of observed aberration yields are different at different doses, one has to account for statistical weights (reciprocal sample variance) for each observation [12].The present study reports on experiments with human lymphocytes exposed to 6°Co 7-rays at dose rates of 0.017 and 0.5 G y -m i n -1. Chromosome aberrations were scored exclusively in Ml-cells and the dose-response was analysed by applying a weighted least squares approximation.Irradiation conditions for whole blood from a healthy male donor were identical to our earlier experiments with 6°Co 7-rays [5]. A detailed description of culture conditions is given elsewhere [1,13]. A total of 29,200 Ml-cells was analysed for both experiments and the dose response for dicentrics and excess acentrics (sum of terminal and interstitial deletions + acentric rings) was determined. Since ringchromosomes were always observed in a frequency of only about one tenth of total dicentrics they were not included in the quantitative analysis. The control data are pooled from 24,000 Ml-cells of 47 unexposed persons analysed in our laboratory (0.38 dicentrics and 3.0 acentrics per 103 cells).

The effect of 220 kVp X-rays with different spectra on the dose response of chromosome aberrations in human lymphocytes

“…However, when compared to our recent findings with 6°Co y-rays no strong influence should be expected. In the gamma-experiments the dose rate differed by about a factor 30 (0.5 and 0.017 Gy • min -1) and b(2)D 2 for dicentric production was found to decrease by 25%, whereas the linear component remained unchanged [3]. It seems unlikely that a dose rate effect of the same order of magnitude should result from the exposure times used in exp.…”

On target cell numbers in radiation-induced H4 - RET mediated papillary thyroid cancer

“…Default assumptions for α HRγ and β HR might then have been the literature values for dicentrics, α dγ =0.01-0.025 Gy -1 and β dγ =0.05-0.06 Gy -2 [41,43]. Knowing, however, that H4 and RET are 30 Mb apart on chromosome 10, a relationship between inter-loci geometric distances and inter-loci genomic distances [35] suggests that S hr (r) be given by Eq.…”

Rbe of 200 Mev Neutron Radiation for the Induction of Chromosomal Abberation in Human Lymphocytes

“…For the experiments, fresh peripheral blood was drawn from the same healthy male donor, as already used in our previous irradiation experiments with monoenergetic neutrons with energies between 0.036 MeV and 14.6 MeV [1], quasi-monoenergetic 60 MeV neutrons [2] and with 60 Co γ-rays [2,3] as reference radiation. The neutron irradiation was carried out at the neutron beam facility [4] of the iThemba Laboratory for Accelerator Based Sciences (iTL) in Somerset West, South Africa using a quasi-monoenergetic neutron beam with a peak neutron energy of 192 MeV.…”

“…These culture conditions ensured that the chromosome analysis could be performed exclusively in complete metaphases of the first cell cycle in vitro. Chromosome preparation and Giemsa staining were carried out according to our earlier experiments [1][2][3]. All slides were coded.…”