title: DNA double-strand break signalling: X-ray energy dependence of residual co-localised foci of gamma-H2AX and 53BP1.
abstract: OBJECTIVE
  The application of ionising radiation for medical purposes requires the investigation of induced and persistent DNA damages, especially for soft X-rays that are assumed to be more effective than higher energy photons. Therefore, we examined the energy dependent time and dose response of residual DNA damage foci for soft X-rays in comparison to 200 kV photons.
  
  
  METHODS
  DNA damage present in cell line 184A1 within 48 h after irradiations with 10 kV, 25 kV and 200 kV photons was analysed by immunochemical detection of co-localised gamma-H2AX (phosphorylated histone H2AX) and 53BP1 (tumour protein 53 binding protein) foci.
  
  
  RESULTS
  The dose dependencies of the colocated foci revealed significant energy dependent differences with increasing amounts of residual foci at decreasing X-ray energy independent on postirradiation time. Dose-dependent RBE (relative biological effectiveness) values ranging from 4 to 7 were determined for 10 kV relative to 200 kV X-rays based on the 24 hour dose responses. For 25 kV photons, ratios considerably higher than one were obtained only for doses above 2 Gy.
  
  
  CONCLUSIONS
  The expected energy dependence with increasing DNA damage at decreasing photon energy was confirmed for the residual co-localised foci measured at different time points after irradiation.
authors.affiliation: Institute of Radiation Physics, Forschungszentrum Dresden-Rossendorf, Dresden, Germany. E.Beyreuther@fzd.de
authors.forename: Elke
authors.initials: E
authors.lastname: Beyreuther
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Lessmann
authors.forename: Jörg
authors.initials: J
authors.lastname: Pawelke
authors.forename: Stefan
authors.initials: S
authors.lastname: Pieck
mesh_terms: D001940:Breast / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects; D002460:Cell Line; D053903:DNA Breaks, Double-Stranded; D004307:Dose-Response Relationship, Radiation; D004847:Epithelial Cells / Q000378:metabolism / Q000528:radiation effects; D005260:Female; D006657:Histones / Q000378:metabolism* / Q000528:radiation effects*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism* / Q000528:radiation effects*; D007700:Kinetics; D008856:Microscopy, Fluorescence; D017785:Photons / Q000009:adverse effects; D015398:Signal Transduction / Q000528:radiation effects; D000071857:Tumor Suppressor p53-Binding Protein 1
chemical_list: C468783:H2AX protein, human; D006657:Histones; D047908:Intracellular Signaling Peptides and Proteins; C498301:TP53BP1 protein, human; D000071857:Tumor Suppressor p53-Binding Protein 1