title: RBE of X rays of different energies: a cytogenetic evaluation by FISH.
abstract: Mammography using 26-30 kVp X rays is routinely used in breast cancer screening. Discussion about the radiation-related risk associated with this methodology is ongoing. For radioprotection purposes, a quality factor of 1 has been assigned for all photon energies. However, the relative biological effectiveness (RBE) could increase as the photon energy decreases. Analyzing different biological parameters, for 30 kVp X rays, RBE values from 1 to 8 have been estimated. In the present study, a cytogenetic FISH evaluation of the RBE of 30, 80 and 120 kVp X rays has been done. Blood samples were irradiated with 10 doses from 0.05 to 3 Gy for each energy studied. The yields of translocations and dicentrics were determined by fluorescence in situ hybridization (FISH) using whole chromosome probes for chromosomes 1, 4 and 11 together with a pancentromeric probe. The alpha coefficients of the dose-effect curves for dicentrics, minimum number of breaks needed to produce exchange-type aberrations, and apparently simple translocations were used to estimate the RBE. Using the curves obtained for 120 kVp as a reference, the RBE values for dicentrics were 1.08+/-0.43 and 1.73+/-0.59 for 80 and 30 kVp X rays, respectively; for minimum number of breaks these values were 1.38+/-0.39 and 1.42+/-0.41, and for apparently simple translocations they were 1.26+/-0.40 and 1.51+/-0.47, respectively. Moreover, the induction of complex aberrations by these energies was compared. The percentage of complex aberrations relative to total aberrations showed a significant tendency to increase as X-ray energy decreased: 7.8+/-1.19, 9.8+/-1.6 and 14.1+/-1.9 for 120, 80 and 30 kVp, respectively (P<0.02).
authors.affiliation: Unitat d'Antropologia Biològica, Departament de Biologia Animal, Biologia Vegetal i Ecologia, Universitat Autònoma de Barcelona, E-08193, Bellaterra, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Mestres
authors.forename: M R
authors.initials: MR
authors.lastname: Caballín
authors.forename: L
authors.initials: L
authors.lastname: Barrios
authors.forename: M
authors.initials: M
authors.lastname: Ribas
authors.forename: J F
authors.initials: JF
authors.lastname: Barquinero
mesh_terms: D000328:Adult; D002478:Cells, Cultured; D003582:Cytogenetics; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008297:Male; D012062:Relative Biological Effectiveness; D014965:X-Rays