Comparison of dose dependence of chromosome aberrations in peripheral lymphocytes at low levels of acute in vitro irradiation with 250 kV X-rays and 14 MeV neutrons

Two studies carried out by 14 different laboratories under the auspices of the IAEA are described. In separate experiments peripheral blood of two donors each was irradiated in vitro with 250 kV X-rays and with 14.8 MeV neutrons at seven dose levels between 3.5 and 300 mGy. The methods of irradiation, culture and scoring techniques are presented and several considerations regarding the data processing are described. The results from the first experiment showed that chromosomal aberration frequencies induced by X-irradiation at dose levels between 10 and 30 mGy are not significantly different from the control values, whereas a significant decrease at 4 mGy was seen. At higher doses the dose effect follows a linear-quadratic relationship with the coefficients α=6.51+-0.72x10-5 and β=11.9+-2.0x10-8 for the total number of chromosome aberrations. From the preliminary results of the second experiment it cannot yet be decided whether the dose effect at 3.4 mGy deviates significantly from the linear dose relationship dominating between 16.4 and 244 mGy with α=41.7+-1.4x10-5 for the totals. The RBE in the upper dose levels is estimated to be between 5.5 and 7.5 for the totals and between 4 and 9 for the dicentrics. (author)