title: Relative biological effectiveness of mammography X-rays at the level of DNA and chromosomes in lymphocytes.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  Blood of five healthy donors was irradiated in vitro with 30 kV X-rays and (60)Co 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Basic Medical Sciences, University of Ghent, Belgium.
authors.forename: Julie
authors.initials: J
authors.lastname: Depuydt
authors.forename: Annelot
authors.initials: A
authors.lastname: Baert
authors.forename: Veerle
authors.initials: V
authors.lastname: Vandersickel
authors.forename: Hubert
authors.initials: H
authors.lastname: Thierens
authors.forename: Anne
authors.initials: A
authors.lastname: Vral
mesh_terms: D002478:Cells, Cultured; D019457:Chromosome Breakage / Q000528:radiation effects*; D004247:DNA / Q000235:genetics* / Q000528:radiation effects*; D004249:DNA Damage / Q000502:physiology*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000502:physiology* / Q000528:radiation effects*; D008327:Mammography; D011829:Radiation Dosage; D012062:Relative Biological Effectiveness; D014965:X-Rays
chemical_list: D004247:DNA