Dependence of the Yield of DNA Double-Strand Breaks in Chinese Hamster V79-4 Cells on the Photon Energy of Ultrasoft X Rays
2001; Radiation Research Society; Volume: 155; Issue: 3 Linguagem: Inglês
10.1667/0033-7587(2001)155[0440
ISSN1938-5404
AutoresC. Malavé Lara, Mark A. Hill, T.J. Jenner, D.G. Papworth, P. O’Neill,
Tópico(s)Radiation Effects and Dosimetry
Resumode Lara, C. M., Hill, M. A., Jenner, T. J., Papworth, D. and O'Neill, P. Dependence of the Yield of DNA Double-Strand Breaks in Chinese Hamster V79-4 Cells on the Photon Energy of Ultrasoft X Rays.Induction of DNA DSBs by low-LET radiations reflects clustered damage produced predominantly by low-energy, secondary electron "track ends". Cell inactivation and induction of DSBs and their rejoining, assayed using pulsed-field gel electrophoresis, were determined in Chinese hamster V79-4 cells irradiated as a monolayer with characteristic carbon K-shell (CK) (0.28 keV), aluminum K-shell (AlK) (1.49 keV), and titanium K-shell (TiK) (4.55 keV) ultrasoft X rays under aerobic and anaerobic conditions. Relative to 60Co γ rays, the relative biological effectiveness (RBE) for cell inactivation at 10% survival and for induction of DSBs increases as the photon energy of the ultrasoft X rays decreases. The RBE values for cell inactivation and for induction of DSBs by CK ultrasoft X rays are 2.8 ± 0.3 and 2.7 ± 0.3, respectively, and by TiK ultrasoft X rays are 1.5 ± 0.1 and 1.4 ± 0.1, respectively. Oxygen enhancement ratios (OERs) of ∼2 for cell inactivation and induction of DSBs by ultrasoft X rays are independent of the photon energy. The time scale for rejoining of DNA DSBs is similar for both ultrasoft X rays and 60Co γ rays. From the size distribution of small DNA fragments down to 0.48 kbp, we concluded that DSBs are induced randomly by CK and AlK ultrasoft X rays. Therefore, ultrasoft X rays are more efficient per unit dose than γ radiation at inducing DNA DSBs, the yield of which increases with decreasing photon energy.
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