Radiotherapy (RT) is still a golden procedure for brain tumour therapy. Ionizing radiation (IR) is IARC carcinogen of group 1 and the use of novel RT techniques increased the precise targeting, dose delivery, localized dose exposure and lowered the number of necessary IR exposures. The use of volatile anaesthetics (VA) in RT helped in patients’ immobility and RT targeting either due to the type of the procedure or due to different patients’ conditions (claustrophobia, anxiety, etc.), considering the increase in brain tumour incidence among adults and children. Isoflurane (ISO) among VA is commonly used due to fast sedation and stable patients’ conditions. Although considered safe, there are reports about its genotoxicity and mutagenicity in vitro, in vivo and in clinical studies but with no consistent and even contradictory results, mostly considering the toxic and protective effects in brain cells. Combined VA-IR effects have not been examined so far, so we decided to test single exposure on brain cells in vivo. 120 Swiss albino male mice, were exposed to 2.4 % ISO® for 2 hours or to 1 or 2 Gy whole body γ-IR ( ⁶⁰ Co, dose rate 1.88 Gy/min) or their combination. Frontal lobe brain samples (as the most sensitive IR damaging parts) were taken immediately (0h), 2, 6 and 24h from the exposure and primary DNA damage was evaluated using alkaline comet assay. In non-irradiated ISO samples slightly higher damage level did not significantly differ from control in all time points. IR only samples had significantly higher damage, with the dose increase. In both combined exposures, after 24 hours, ISO significantly decreased damage levels, compared to IR samples and demonstrated its influence on increased velocity repair of the rest of IR damage. Adaptive response, by activating DNA repair mechanisms and the levels of reactive free oxygen radicals’ scavengers are possible mechanism of isoflurane protective effect but further research should be focused on determining the exact mechanisms.

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