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 produce a single photoelectron with a track length of < 7 nm, on the production of structural chromosome-type changes. Materials and methods: Untransformed human fibroblasts (HF12) were irradiated in G1 phase. Aberrations were analysed using fluorescence in situ hybridization using multi-coloured chromosome specific DNA probes for chromosomes 1 and 2 and an α-satellite pan-centromeric probe. Results: C(K) X-rays have a high efficiency per unit absorbed dose for producing simple and complex exchanges. Mean absorbed doses of 0.33-1.31 Gy produce simple exchanges with a predominantly linear dose dependency, and visibly complex exchanges increased by more than the power 2 of the dose, with no evidence of a linear component. The proportion of exchanges that are visibly complex ranged from 9% to 46%. Conclusions: The linear response for simple exchanges provides further support to the hypothesis that damaged DNA may be able to interact with undamaged DNA. The high proportion of complex exchanges may be due to the increased efficiency of double-strand break induction and to the high density of tracks per unit absorbed dose targeting pre-existing sites, some of which may be close to the incident nuclear membrane.