Relative biological effectiveness of mammography X-rays at the level of DNA and chromosomes in lymphocytes

Abstract

Purpose: In many countries, breast cancer screening programs based on periodic mammography exist, giving a large group of women regularly a small dose of ionizing radiation. In order to assess the benefit/risk ratio of those programs the relative biological effectiveness (RBE) of mammography X-rays needs to be determined.

Materials and methods: Blood of five healthy donors was irradiated in vitro with 30 kV X-rays and ⁶⁰Co γ-rays with doses between 5 and 2000 mGy. The phosphorylated histone subtype H2A isoform X-foci (γH2AX-foci) technique was used to quantify the number of DNA double-strand breaks (DSB) after irradiation. Chromosomal damage resulting from non- or misrepaired DNA DSB was quantified with the micronucleus (MN)-assay and the sensitivity was improved by counting only centromere negative micronuclei (MNCM−).

Results: The threshold detection dose obtained with the γH2AX-foci test was 10 mGy for mammography X-rays compared to 50 mGy for γ-rays. With the MN-assay respectively MN-centromere-assay threshold detection doses of 100, respectively, 50 mGy were obtained for mammography X-rays compared to 200 respectively 100 mGy for γ-rays. An RBE of 1.4 was obtained with the γH2AX-foci assay. With the MN-assays low-dose RBE values between 3 and 4 were determined.

Conclusion: Our results indicate that exposure to mammography X-rays resulted in a modest increase in the induction of DSB compared to γ-rays. However, due to the higher linear energy transfer (LET) of mammography X-rays more clustered DNA damage is produced that is more difficult to repair and results in a more pronounced increase in micronucleus formation.

Keywords::

• Micronucleus
• γH2AX-foci
• RBE
• mammography X-rays
• breast cancer

Acknowledgements

The authors are grateful to the volunteers who donated the blood samples.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

The work was supported by a University Development Cooperation ‘VLIR Own Initiative Programme’ between Belgium and South Africa (ZEIN 2005PR309, ZEIN2011PR387).