EFFECTIVENESS OF 0.28 KEV CARBON K ULTRASOFT X-RAYS AT PRODUCING SIMPLE AND COMPLEX CHROMOSOME EXCHANGES IN HUMAN FIBROBLASTS IN-VITRO DETECTED USING FISH

Purpose: To study the effects of carbon K ultrasoft X-rays, which prod uce a single phoroelectron with a track length of <7 nm, on the produc tion of structural chromosome-type changes. Materials and methods: Unt ransformed human fibroblasts (HF12) were irradiated in G1 phase. Aberr ations were analysed using fluorescence in situ hybridization using mu lti-coloured chromosome specific DNA probes for chromosomes 1 and 2 an d an alpha-satellite pan-centromeric probe. Results: C-K X-rays have a high efficiency per unit absorbed dose for producing simple and compl ex exchanges. Mean absorbed doses of 0.33-1.31 Gy produce simple excha nges with a predominantly linear dose dependency, and visibly complex exchanges increased by more than the power 2 of the dose, with no evid ence of a linear component. The proportion of exchanges that are visib ly complex ranged from 9% to 46%. Conclusions: The linear response for simple exchanges provides further support to the hypothesis that dama ged DNA may be able to interact with undamaged DNA. The high proportio n of complex exchanges may be due to the increased efficiency of doubl e-strand break induction and to the high density of tracks per unit ab sorbed dose targeting pre-existing sites, some of which may be close t o the incident nuclear membrane.