Analytical model of chemical phase and formation of DSB in chromosomes by ionizing radiation

Abstract

Mathematical analytical model of the processes running in individual radical clusters during the chemical phase (under the presence of radiomodifiers) proposed by us earlier has been further developed and improved. It has been applied to the data presented by Blok and Loman characterizing the oxygen effect in SSB and DSB formation (in water solution and at low-LET radiation) also in the region of very small oxygen concentrations, which cannot be studied with the help of experiments done with living cells. In this new analysis the values of all reaction rates and diffusion parameters known from literature have been made use of. The great increase of SSB and DSB at zero oxygen concentration may follow from the fact that at small oxygen concentrations the oxygen absorbs other radicals while at higher concentrations the formation of oxygen radicals prevails. It explains the double oxygen effect found already earlier by Ewing. The model may be easily extended to include also the effects of other radiomodifiers present in medium during irradiation.

Applying Petri nets to modeling the chemical stage of radiobiological mechanism

“…This value is in good agreement with our earlier fit [6] obtained for clusters forming DSBs in DNA molecules under similar conditions: cluster diameter of approximately 27 nm; and transmitted energy of 300 eV. We have already studied the effect of the chemical phase on the DSB formation on the basis of differential equations (introduced in Section 2) (see [3][4][5][6][7]). In these papers, however, the results have been gained under some substantial simplifications (e.g.…”

“…It has been derived in [6] by fitting experimental data that in the case of Co60 radiation the size of clusters efficient in DSB formation has been approximately t 13 ns 0 ≅ , which has corresponded to r 13.5 nm 0 ≅ . The corresponding value will also be used in our approach.…”

“…As already mentioned our main aim has concerned the influence of processes in chemical phase on the efficiency of DSB formation in DNA molecules. Our basic model has been applied to the data presented by Blok and Loman [9] concerning the formation of DSB in DNA molecules dissolved in water containing different oxygen amounts during irradiation by Co60 radiation [6]. Under the assumption of standard yield radical number ratios (shown higher) the following initial average radical numbers have been obtained for efficient radical clusters: The initial average size of clusters has been 27 nm which has corresponded to t 13 ns 0 = .…”

“…We have started to study the corresponding problem already earlier, the contemporary result of chemical reactions and cluster diffusion having been described with the help of corresponding differential equations (see [3][4][5][6][7]). The average excitation energy of efficient clusters (in the case of Co60 radiation [6]) should be approximately 300 eV (estimated according to results obtained in radiation chemistry studies).…”

“…The average excitation energy of efficient clusters (in the case of Co60 radiation [6]) should be approximately 300 eV (estimated according to results obtained in radiation chemistry studies). We should ask, however, how the efficiency of corresponding individual clusters changes in dependence on their sizes.…”