Thermal effect of ir radiation at 1273 nm during direct photogeneration of singlet oxygen for solid tumors therapy

Singlet oxygen is an electronically excited state of normal triplet oxygen that has cytotoxic effects. The generation of singlet oxygen as a result of photodynamic therapy is used for the treatment of solid tumors. Methods of singlet oxygen direct photogeneration in tissues using infrared lasers can become an effective alternative to photodynamic therapy. The use of pulsed laser irradiation at 1273 nm with high peak power density is a promising direction. Such modes minimize thermal effects and allow for high peak rates of singlet oxygen generation. In this study, a physical-mathematical model was used to describe the generation of singlet oxygen, taking into account the distribution of radiation intensity and temperature in biological tissues. As a result of numerical modeling, modes of direct photogeneration of singlet oxygen by a 1273 nm laser were calculated when irradiating a wide beam (radius 5 mm) of biological tissue, which did not lead to heating above the biocritical temperature of 42.5°C, but allowed for the generation of cytotoxic amounts of singlet oxygen. On a bio-mimicking gel, it was shown that the irradiation modes used (average power density ~1 W/cm2) did not lead to heating of the site of exposure above biocritical temperatures. The obtained results are a necessary basis for further research on direct photogeneration of singlet oxygen in living systems with the aim of developing innovative methods for the therapy of solid tumors and their implementation in practical oncology.