title: Double-strand break induction and repair in V79-4 hamster cells: the role of core ionisations, as probed by ultrasoft X-rays.
abstract: OBJECTIVE
  To compare the induction of double-strand breaks (DSB) in cells irradiated by 250 and 350 eV ultrasoft X-rays and assess the residual yield of breaks 2 hours post irradiation in order to unravel the correlation between the sharp increase in cell-killing efficiency of ultrasoft X-rays above versus below the carbon-K threshold (284 eV) and the induction of core events in DNA atoms.
  
  
  METHODS
  V79-4 hamster cells were irradiated with synchrotron ultrasoft X-rays at isoattenuating energies of 250 eV and 350 eV. DSB were quantified using pulse field gel electrophoresis.
  
  
  RESULTS
  A significant increase in DSB induction was observed for 350 eV ultrasoft X-rays above the carbon-K threshold, compared to 250 eV below the threshold, per unit dose to the cell. The DSB induced by the 350 eV ultrasoft X-rays were less repaired 2 h after irradiation.
  
  
  CONCLUSIONS
  The increased DSB induction at 350 eV is attributed to the increase in the relative proportion of photon interactions in DNA resulting in significant dose inhomogeneity across the cell with a local increase in dose to DNA. It results from an increase in carbon-K shell interactions and the short range of the electrons produced. Core ionisations in DNA, through core-hole relaxation in conjunction with localised effects of spatially correlated low-energy photo- and Auger-electrons lead to an increase in number and the complexity of DSB.
authors.affiliation: Institut de Minéralogie et de Physique des Milieux Condensés, Université Pierre et Marie Curie-Paris6, UMR-CNRS 7590, Paris, France. penhoat@impmc.jussieu.fr
authors.forename: Marie-Anne Hervé
authors.initials: MA
authors.lastname: du Penhoat
authors.forename: Anne
authors.initials: A
authors.lastname: Eschenbrenner
authors.forename: François
authors.initials: F
authors.lastname: Abel
authors.forename: Arnaud
authors.initials: A
authors.lastname: Boissiere
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Guigner
authors.forename: Annie
authors.initials: A
authors.lastname: Chetioui
authors.forename: Marie-Françoise
authors.initials: MF
authors.lastname: Politis
authors.forename: Alain
authors.initials: A
authors.lastname: Touati
authors.forename: Evelyne
authors.initials: E
authors.lastname: Sage
authors.forename: Terry J
authors.initials: TJ
authors.lastname: Jenner
authors.forename: David L
authors.initials: DL
authors.lastname: Stevens
authors.forename: Mark A
authors.initials: MA
authors.lastname: Hill
mesh_terms: D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects*; D004260:DNA Repair / Q000502:physiology / Q000528:radiation effects*; D004586:Electrophoresis; D011874:Radiometry; D013997:Time Factors; D014965:X-Rays