Two types of double-strand breaks in electron and photon tracks and their relation to exchange-type chromosome aberrations |
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Authors: | V Michalik D Frankenberg |
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Institution: | 1. Radiation Dosimetry Department, Nuclear Physics Institute, Na Truhlárce 39, CZ-18086, Praha 8, Czech Republic 2. Abteilung Klinische Strahlenbiologie und Klinische Strahlenphysik, Zentrum Radiologie, Universit?t G?ttingen, Von Siebold Strasse 3, D-37075, G?ttingen, Germany
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Abstract: | Yields of DNA double-strand breaks (dsb), i. e. the average number of dsb, N–, per relative molar mass, M
r
, and dose, D, produced by electrons and photons in the energy range 50 eV – 1 MeV were calculated. The experimental data of dsb induction
by ultrasoft x-rays and by photons agree well with the calculated yields of dsb as a function of photon energy. The dsb are
classified into simple and complex ones. Energy transfers of less than about 200 eV producing at least two ionizations generate
mainly simple dsb, while low-energy electrons with an initial energy between 200 and 500 eV induce preferentially complex
dsb. Assuming that dsb is the main DNA lesion leading to exchange-type chromosome aberrations (etca), three different mechanisms
have to be considered: 1) complex dsb on its own; 2) interaction between two dsb induced by the same primary particle; and
3) interaction between two dsb induced by different primary particles. Mechanisms 1) and 2) produce a linear term, whereas
mechanism 3) leads to a quadratic term for the yield of etca. The sum of contributions 1) and 2) to the yield of dicentrics
describes fairly well the non-trivial structure of the experimental data. The results suggest that interaction between complex
dsb does not contribute significantly to the formation of dicentrics via mechanism 3).
Received: 30 July 1995 / Accepted in revised form: 28 March 1996 |
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