Single- and Double-Strand Breaks of Dry DNA Exposed to Protons at Bragg-Peak Energies

Abstract

Ultrathin layers (<20 nm) of pBR322 plasmid DNA were deposited onto 2.5 μm thick polyester films and exposed to proton Bragg-peak energies (90-3000 keV) at various fluences. A quantitative analysis of radio-induced DNA damage is reported here in terms of single- and double-strand breaks (SSB and DSB, respectively). The corresponding yields as well as G-values and the cross sections exhibit fairly good agreement with the rare available data, stemming from close experimental conditions, namely, based on α particle irradiation. SSB/DSB rates appear to be linear when plotted against linear energy transfer (LET) in the whole energy range studied. All the data present a maximum in the 150-200 keV energy range; as for LET, it peaks at 90 keV. We also show that fragmentation starts to be significant for proton fluences greater than 1 × 10 cm at the Bragg-peak energies. Finally, we determine the average proton track radial extension, r, corresponding to an occupation probability of 100% DSB in the Bragg-peak region. The r values determined are in excellent agreement with the radial extensions of proton tracks determined by simulation approaches in water. When plotted as a function of LET, both SSB and DSB cross sections bend back at high LETs.

Clinically relevant nanodosimetric simulation of DNA damage complexity from photons and protons

“…However, there is considerable variability in the experimental data. For example, the data from Vyšín et al 65 and Souici et al 66 are from experiments with the same plasmid (pBR322) and under similar conditions. Although the studies do not investigate the same LET t range, extrapolation of the results would suggest disagreement in measured strand break yields.…”

“…To assess the simulation's predictive accuracy of DNA damage over a greater range of LET t , three further studies were included. Similarly, Souici et al 66 irradiated dry pBR322 with proton LET t relevant to the Bragg peak region. Urushibara et al 67 and Ushigome et al 68 studied the direct DNA damage yields by irradiating hydrated pUC18 plasmids with alpha particles.…”

Inactivation cross section induced by heavy ions of different energies in Bacterial cells of E. coli: An analytical approach

“…Heavy ions induced inactivation and mutagenic effect in microorganisms such as yeast cells which provide astronauts needs in active space exploration was studied (Wang el al., 2010). Quantitative analysis of radio-induced DNA damage exposed to protons at Bragg-peak energy was given by Souici et al, (Souici et al, 2017).…”

Calculation of survival probabilities for cells exposed to high ion fluences

“…These doses are not very large, which means that the fluences of protons or heavier ions are small enough so that the ion tracks do not overlap with each other. However, in many in vitro experiments, larger doses are used [10,11,12,13]. Then such an overlap is expected.…”