Radiation-Induced Bystander Effect via GRID Radiotherapy and Medium Transfer in the A-375 Human Melanoma Cancer Cell Line: An In-vitro Study

Purpose: The goal of this research was to investigate the bystander effect in the A-375 cell line under the spatially fractionated radiation therapy (GRID therapy technique). In GRID therapy, due to direct and indirect cell damage after high-dose radiation, evaluation of Radiation-Induced Bystander Effects (RIBE) is of the most importance for investigating the risk of therapy. Materials and Methods: The potential role of RIBE was evaluated with different doses of 6 MeV electron radiation and different incubation times after irradiation using two methods; GRID therapy and medium transfer. Colony Formation Assay (CFA) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) test were used to detect the mentioned effects. Alpha and beta parameters were calculated from the cell survival curve by the quadratic-linear model. Results: The result showed that the survival fraction significantly decreases by increasing the radiation dose for both bystander and irradiated cells. However, a decrease in the number of colony-forming cells caused by electron radiation greater than 4MeV to target cells was significantly increased compared with bystander cells (P lt; 0.05). While increasing the incubation time after exposure to an electron beam, it had no significant effect on cell survival fraction (P gt; 0.05). Furthermore, the RIBE level in non-target cells increased up to a dose of 4Gy, but decreased significantly at doses higher than 4Gy. This result in high doses confirmed that a negative feedback mechanism was responsible for reducing the RIBE response. Conclusion: Based on the results, we can state there are classic radiation-induced bystander effects in A-375 monolayer exposed by GRID therapy and medium transfer technique, which can play an important role in pre-clinical and clinical studies.