Regular Article

Initial radiation DNA damage observed in prematurely condensed chromosomes of G2-phase human lymphocytes and analytical model of ion tracks^⋆

¹ Department of Physics and Chemistry, Maritime University of Szczecin, Wały Chrobrego 1-2, 70-500 Szczecin, Poland
² Institute of Physics, University of Szczecin ul. Wielkopolska 15, 70-451 Szczecin, Poland
³ Joint Institute for Nuclear Research, Joliot-Curie 6, 141980 Dubna, Russia

^a e-mail: a.kowalska@am.szczecin.pl

Received: 28 February 2019
Received in final form: 20 November 2019
Published online: 28 January 2020

Abstract

In the present work, we have adopted the premature chromosome condensation (PCC) technique to study the initial DNA damage in order to distinguish between the biological and physical components of the dose-effect curves. We have studied G₂-chromatid breaks in human lymphocytes, isochromatid-type breaks as well as chromatid exchanges at two different sampling times: directly after irradiation (t₀) and 12 hours later (t₁₂). The lymphocyte samples have been exposed to 150 MeV and spread out Bragg peak (SOBP) proton beams, 22 MeV/u ¹¹B ions and for comparison to ⁶⁰Co γ rays. Dose-response curves for both types of breaks have been determined. We have shown that t₀ G₂-chromatid breaks follow linear-quadratic dependence for all studied cases and could be used for estimation of the effective ion track radius. A comparison to the expected physical track radii leads to the conclusion that the biological repair mechanism considerably prevails the physical effect of the overlapping ion tracks even at the time t₀. The results have been also compared to the dose-effect curves previously obtained in our chromosome aberrations study.