Radioprotective effect of melatonin against flattening filter-free irradiation-induced rat parotid gland damage

The purpose of the present study is to investigate the protective effect of melatonin against early period parotid gland damage, caused by low- and high-dose rate beams in different dose plans, by using experimental rat models. Eighty Sprague Dawley rats were divided into ten randomized groups, each group being different in terms of dose plan and dose rate. Subjects in the control group were given only sodium chloride. Subjects in the melatonin-only group received 10 mg/kg melatonin. The head and neck region of each rat in radiotherapy only and radiotherapy plus melatonin group was irradiated with single dose (SD) and fractional dose (FD) Flattening Filter (FF) and Flattening Filter-Free (FFF) beams. Radiotherapy plus melatonin group subjects were administered 10 mg/kg melatonin 15 min before radiotherapy, radiotherapy only group did not receive melatonin treatment. Ten days after radiotherapy, the parotid gland of rats was examined for histopathological changes and blood samples were collected for biochemical analysis. When radiotherapy only groups and the control group are compared, for both FF, FFF beam modes and single, fractional dose plans, we observed statistically significant difference in histopathology and biochemical parameters due to irradiation. Melatonin administration in radiotherapy plus melatonin groups contributed to conserving these parameters (p < 0.05). In conclusion, melatonin acts as a significant protective agent against early rat parotid gland damage in varying dose plans for both FF and FFF beams. A difference in radiation-induced damage was not observed between FF and FFF beams using in vivo rat model.