Purpose: In order to evaluate DNA damage induced by protons at low and radiotherapeutic doses at the therapeutic proton complex at Ružomberok, Slovak Republic, lymphocytes from umbilical cord blood (UCB) of the same four probands were irradiated in the dose range of 1–200 cGy with γ-rays and protons (200 MeV, irradiation in the Bragg peak). Materials and methods: DNA repair γH2AX/53BP1 foci were analyzed by fluorescent microscopy and flow cytometry. Results: Statistically significant effects of radiations were detected by fluorescent microscopy at all doses higher 1 cGy. Almost all distributions of foci in irradiated cells fitted to the Poisson distribution. In general, there was no difference in the levels of γH2AX and 53BP1 foci in irradiated cells. Flow cytometry was less sensitive and detected radiation induced effects at doses of 50 cGy and higher. Factorial analysis of variance in the whole studied dose range has shown no significant effect of radiation quality on number of γH2AX and 53BP1 foci. The ratio of proton-induced foci to γ-ray-induced foci was 0.86 ± 0.16 (53BP1) and 0.99 ± 0.34 (γH2AX) as measured by fluorescent microscopy and 0.99 ± 0.16 (γH2AX) as measured by flow cytometry at the radiotherapeutic dose of 2 Gy. Conclusions: Both flow cytometry and fluorescent microscopy indicated that the average value of relative biological efficiency (RBE) at radiation doses ≥ 20 cGy was about 1.0. Our data that RBE increased at low doses ≤ 20 cGy are relevant both to the development of treatment modalities and exposures that take place during space exploration and should be verified by further studies.

The early delayed effects of accelerated carbon ions and protons on the cognitive functions of mice using tests of the total activity, spatial learning, and long-term and short-term hippocampal-dependent memory were studied. The obtained results showed that irradiated animals do not develop an altered behavioral pattern: the level of anxiety is not increased, the exploratory model of behavior is clearly pronounced, and there is no deficiency of hippocampal-dependent memory. However, the long-term memory test revealed fewer errors in finding an escape box in a group of animals irradiated with protons compared to the control animals and mice irradiated with carbon ions. The results may indicate a better preservation of memory traces under these conditions.

This work focuses on the study of remote effects (duration of remission, recurrence rate, and average lifespan) in mice with Ehrlich ascites carcinoma exposed to oligofractionated irradiation with a pencil scanning beam of protons depending on the volume of the tissue being irradiated and the interval between dose fractions. The results show higher antitumor efficacy and a considerable increase in the average life span of mice after hypofractionated irradiation with a pencil scanning beam of protons at a total dose of 60 Gy of the gross tumor volume compared with the planning target volume.