title: Characteristic 8 keV X rays possess radiobiological properties of higher-LET radiation.
abstract: Electronic brachytherapy systems are being developed that can deliver X rays of varying energy depending on the material of a secondary target. A copper target produces characteristic 8 keV X rays. Our aim was to determine whether 8 keV X rays might deliver greater biological effectiveness than megavoltage photons. Cells of the U251 human glioma cell line were used to compare the biological effects of 8 keV X rays and (60)Co gamma rays in terms of relative biological effectiveness (RBE), oxygen enhancement ratio (OER), and DNA damage. The RBE at 50% and 10% survival was 2.6 and 1.9, respectively. At 50% survival, the OER for cells treated with 8 keV X rays was 1.6 compared with 3.0 for (60)Co gamma rays. The numbers of H2AX foci per Gy after treatment with 8 keV X rays and (60)Co gamma rays were similar; however, the size of the foci generated at 8 keV was significantly larger, possibly indicating more complex DNA damage. The mean area of H2AX foci generated by 8 keV X rays was 0.785 microm(2) (95% CI: 0.756-0.814) compared with 0.491 microm(2) (95% CI: 0.462-0.520) for (60)Co gamma rays (P < 0.0001). Characteristic 8 keV X rays produce two to three times the biological effectiveness of megavoltage photons, with a radiobiological profile similar to higher-LET radiations.
authors.affiliation: Wayne State University, Detroit, Michigan 48201-2013, USA.
authors.forename: Ravi
authors.initials: R
authors.lastname: Shridhar
authors.forename: William
authors.initials: W
authors.lastname: Estabrook
authors.forename: Mark
authors.initials: M
authors.lastname: Yudelev
authors.forename: Joseph
authors.initials: J
authors.lastname: Rakowski
authors.forename: Jay
authors.initials: J
authors.lastname: Burmeister
authors.forename: George D
authors.initials: GD
authors.lastname: Wilson
authors.forename: Michael C
authors.initials: MC
authors.lastname: Joiner
mesh_terms: D001918:Brachytherapy; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000528:radiation effects; D003037:Cobalt Radioisotopes; D004249:DNA Damage; D005720:Gamma Rays; D005909:Glioblastoma / Q000473:pathology / Q000532:radiotherapy; D006801:Humans; D018499:Linear Energy Transfer; D010100:Oxygen / Q000378:metabolism; D012062:Relative Biological Effectiveness; D014965:X-Rays
chemical_list: D003037:Cobalt Radioisotopes; D010100:Oxygen