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RESTORATIVE RECOVERY OF IRRADIATED TISSUE

Radiation therapy undoubtedly has an effective anticancer effect and is an integral part of cancer therapy. Approximately 2/3 of all patients receive radiation therapy within the scope of treatment. However, radiation therapy can have an undesirable effect on healthy tissue included in the radiation field, especially on bone tissue. Necrotic bone changes, called osteoradionecrosis, are among the most adverse post-radiation complications. The mechanism of tissue damage is associated with the development of ischemia, cell apoptosis and fibrosis at the site of radiation. Also in patients with a long life span, the risk of developing post-radiation sarcoma is increased, it exceeds 0.8% in comparison with the group that underwent radiation therapy without complications.

RESTORATIVE RECOVERY OF IRRADIATED TISSUE

Clinical observations. Treatment of head and neck tumors allows achieving good oncological results, but in some cases it leads to the development of aesthetic and functional defects. The use and benefits of reconstructive surgery in the treatment of post-radiation injuries are undeniable, especially the technique of the Kole Man, which includes transplantation of adipose tissue into the irradiated areas. We have experience in performing this plastic surgery in 13 patients who have applied to our center for the reconstruction of post-radiation defects of the skin and mucous membranes. Both aesthetic and functional results have been achieved and the quality of life of the patients has been improved. These clinical improvements have been compared with morphological data. Thus, we assumed that the clinical improvement was due to increased blood supply and as a result, improved tissue regeneration. Cellular composition such as fat and me-zenchymal stem cells contained in fat tissue potentiates angiogenesis, which leads to revascularization and improved blood supply in ischemized irradiated tissues. In order to study in more detail the cellular and tissue mechanisms underlying these changes, we conducted a study.

RESTORATIVE RECOVERY OF IRRADIATED TISSUE

Experimental data. In order to simulate post-radiation damage, an experimental model of radio-induced defect using animals was developed. As the object of the study we used rats, which were bilaterally irradiated to the hind limb at a dose of 30 to 50 Gy. The estimation in dynamics was carried out by successive registration of changes with the help of scintigraphy. Histological, immunohistochemical studies and assessment of growth factors (IL-1, IL-2, IL-6, IL-10, IFN-y, TNF-a, VEGF, GM-CSF, TGF-pU by immunoanalysis were also performed. After irradiation, all animals developed acute and distant post-radiation damage, the intensity of these effects was much higher in the group exposed to 50 Gy. Acute foot necrosis was developed, spreading gradually to the whole lower limb. Quantitative analysis was performed by estimating the absorption of 99mTc-ethylcysteine dimer by photon emission computed tomography.

The blood supply in animals irradiated with 30g dose was the same as in the control group. However, when assessing the blood supply in the ischemized limb (2 months later) in animals exposed to a dose of 50g, in comparison with the control group a significant decrease in blood supply was observed. A significant reduction of 99mTC-HDP uptake by bone tissue in both 30g and 50g groups was also noted. In comparison with a normal limb, the rate of reduction of the preparation absorption by bone tissue in the group of animals irradiated with 50gr dose was reduced and made up (-29% for 8 months). In 50g of group, maximum reduction of preparation absorption was observed in 2 months and made (-31%), then the rate of reduction decreased and stabilized by 8 months (-21%). At histological examination of the group irradiated with 30g of dose, such changes as edema and fibrosis, vascular sclerosis and heteration were revealed.