Radiobiological comparison of flattening filter (FF) and flattening filter-free (FFF) beam in rat laryngeal tissue.

Purpose: The purpose of this study is to investigate the radioprotective effect of melatonin by analyzing histopathological changes and serum biochemical levels on experimental rat models exposed to flattening filter (FF) and flattening filter-free (FFF) beam.

Materials And Methods: Forty-eight healthy adult Sprague Dawley rats were randomly divided into six groups. The control (Group 1) was given no treatment, the melatonin (Group 2) was given 10 mg/kg melatonin only, the FF (Group 3) and FFF (Group 5) were given fractionated dose (Total 32 Gy, 5 consecutive days) radiotherapy only, and the FF plus melatonin (Group 4) and FFF plus melatonin (Group 6) were given 10 mg/kg melatonin 15 minutes prior to irradiation. Rats were examined for histopathology and biochemical analysis 10 days after irradiation.

Results: When results of FF and FFF radiotherapy only groups are compared to control group, statistically significant difference in histopathological and biochemical parameters are observed; however, melatonin administration in radiotherapy plus melatonin groups improved these parameters ( <.05). In addition, there was no statistically significant difference between FF and FFF beams ( > .05).

Conclusions: The effect of low- and high-dose beams on the rat larynx and serum samples were investigated histopathologically and biochemically for the first time. We observed that melatonin supplemented before FF and FFF radiotherapy protected early period radiotherapy-induced laryngeal mucosal damage. Since the radiobiological results of FF and FFF beams are similar, FFF beams can be safely applied in laryngeal irradiation. However, more experimental rat and clinical studies are needed to clarify the radiobiological uncertainy concerning dose rate on cancerous and healthy tissue.