For many years, photobiomodulation in cancer patients has been used empirically, based on the positive clinical experience. When using PBM for the prevention and treatment of early radiation toxicity, exposure can occur directly in the area of the tumor site. For that reason, the data is need about a potential influence of low-intensity red light as on the normal as well on the tumor cells exposed to ionizing radiation. The aim of the work was to study the effects of photobiomodulation (PBM) in the red spectrum (640 nm) with fluences from 3 mJ/cm2 to 2 J/cm2 in combination with ionizing radiation at doses of 2–6 Gy against human BJ-5ta-hTERT cells – postnatal fibroblasts. The cells were exposed to low-intensity red light before or after their exposure to IR, the viability of the cells was determined by MTT-test 24 hours after the last exposure. The effects of PBM depend on the fluence of PBM, the dose of IR and the sequence of the actions of these physical factors on cells. The adaptive effect of PBM was observed only for high fluences – 1 and 2 J/cm2 when exposed to PBM and subsequent irradiation of IR. At the same time, the stimulating effect of PBM was observed only for low fluences from 3 to 300 mJ/cm2 under IR irradiation and subsequent (after 1 hour) exposure to PBM. These data should be taken into account when using PBM for the correction of adverse events of radiation therapy in a clinic.
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