Comparison of transformation, chromosome aberrations, and reproductive death induced in cultured mammalian cells by neutrons of different energies.

Dose-effect relations for cell transformation and reproductive death induced in C3H/10T1/2 cells, NBCH-3 cells, and WAGR-2 cells by 300 kV X rays and monoenergetic fast neutrons of 0.5, 4.2, and 15 MeV energy have been analyzed on the basis of the relations F(D) = t1D + t2D2 and S(D)/S(0) = exp - (a1D + a2D2), respectively. Values of a1 are a factor of about 10(3) larger than corresponding values of t1, while the dependence on neutron energy is similar for both effects. RBE values and relations between the a1 and t1 values are compared with characteristics, derived from corresponding parameters for chromosome aberrations and reproductive death, induced in other cell lines after irradiation with the same neutron beams. A hypothesis is developed assuming that nonrandom structural changes at a restricted number of sites on one or more chromosomes are the primary causes of transformation of cultured mammalian cells by ionizing radiations, whereas similar but randomly distributed chromosomal changes, which are induced at many sites on all chromosomes, cause observable aberrations and reproductive death. Flow cytometry of chromosome suspensions has been used to demonstrate nonrandom changes of chromosomes in selected clones of transformed cells and of random changes of chromosomes in cells inactivated by X rays and neutrons.