FISH-based analysis of 10- and 25-kV soft X-ray–induced DNA damage in 184A1 human mammary epithelial cells

Abstract

Over the past years, several in vitro studies have been performed on DNA damage induced by soft X-rays, especially in the energy range below 50 keV. Radiation effects originating from such low-energy photons are relevant in the context of medical diagnostics, for example, mammography, or of accidental exposure to scattered radiation. The present study was initiated to investigate the X-ray energy-dependent induction of stable and unstable chromosomal aberrations in the human mammary epithelial cell line 184A1. Three colour fluorescence in situ hybridisation was applied to identify chromosomal damage in chromosomes 1, 8 and 17, induced by 10-kV or 25-kV soft X-rays as well as by 200-kV X-rays as a reference quality. The overall results confirm the X-ray energy dependencies published for human lymphocytes showing increasing chromosomal aberration frequencies and higher aberration complexity with decreasing X-ray energy and increasing dose. Comparing the obtained dose dependencies, ratios of 0.84 ± 0.09 and 1.22 ± 0.18 were revealed for stable translocations induced by 25- and 10-kV X-rays, respectively, using 200-kV X-rays as reference. Moreover, the analysis of the minimum number of breaks required to form the visible chromosomal damage resulted in similar ratios of 0.93 ± 0.07 for 25-kV X-rays and 1.25 ± 0.10 for 10-kV X-rays relative to 200-kV X-rays. In addition, non-DNA-proportional contributions of chromosomes 8 and 17 to the whole DNA damage and deviations from the expected 1:1 ratio of translocations and dicentrics were observed for cell line 184A1.

Unstable Chromosome Aberrations Do Not Accumulate in Normal Human Fibroblast after Fractionated X-Irradiation

“…The generator was operated at 30 mA and at 90 kV for the delivery of 0.1 Gy or at 18 mA and at 200 kV for the delivery of 0.2, 0.5, or 1 Gy. The quality of X-ray related with kV would not influence the RBE so much since the effect of the quality may be much smaller than of exposure dose [32, 33]. The generator was equipped with a filter system composed of a plate comprising 1-mm copper and 1-mm aluminum for 0.1 Gy or a plate comprising 0.5-mm copper and 0.5-mm aluminum for 0.2 Gy, 0.5 Gy, or 1 Gy.…”

Relative biological effectiveness of low-energy X-rays (25 kV) in mutant p53 cancer cells

“…Likewise, FISH-based examination of complex chromosomal damages in terms of translocations and dicentrics in 184A1 cells revealed increasing frequency and complexity of chromosomal aberrations with decreasing X-ray energy associated with RBE values of 0.84 ± 0.09 at 25 kV and 1.22 ± 0.18 at 10 kV. The minimum number of DNA strand breaks to build a visible chromosomal damage resulted in similar RBE ratios of 0.93 ± 0.07 (25 kV) and 1.25 ± 0.10 (10 kV) (Beyreuther et al 2012). In MCF-10A cells receiving a single mammogram, Mills et al, (2015) calculated an RBE of 29 kV X-rays relative to 137 Cs radiation of 1.1 ± 0.2 for DNA double-strand breaks based on 53BP1 foci assay representing no significant difference between the radiation qualities.…”

“…The International Commission on Radiological Protection recommends a weighting factor w R = 1 for photons of all energies (ICRP 2007). In contrast, in vitro studies suggest that the RBE varies depending on photon energy, cell line and biological end point (Paget et al 2019), with low-energy X-rays being more effective per unit dose than photons of higher energies (Beyreuther et al 2012;Heyes et al 2006). X-ray irradiation of non-tumourigenic breast epithelial cell lines revealed RBE values in MCF-12A cells for clonogenic survival and micronuclei formation of 1.1-1.4 at 25 kV (Lehnert et al 2006) and 1.2-4.1 at 10 kV relative to 200 kV photons (Lehnert et al 2008).…”

Radiobiology experiments with a laser driven x-ray source: Exploring the UHDR regime

“…The setup presented here is characterized by dose concentration in ultra-short pulses. In addition, it allows for studying DNA damage induced by low-energy xrays (<30 keV) which can differ significantly from those at 100-200 keV and beyond [13,14].…”