Tehran University of Medical Sciences Frontiers in Biomedical Technologies 2345-5837 10 3 2023 06 01 339 348 Marzieh Nabikhani Medical Physics Department, School of Medicine, International Campus-Iran of Medical Sciences, Tehran, IRAN Samideh Khoei Iran University of Medical Sciences Seied Rabi Mahdavi Department of Medical Physics, School of Medicine, Iran University of Medical Sciences, Tehran Jila Rajaee Department of Medical Physics, School of Medicine, Iran University of Medical Sciences, Tehran Sakine Shirvalilou Finetech in Medicine Research Center, Iran University of Medical Sciences, Tehran, Iran 2022 06 16 2022 09 05 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 < 0.05). While increasing the incubation time after exposure to an electron beam, it had no significant effect on cell survival fraction (P > 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. https://fbt.tums.ac.ir/index.php/fbt/article/view/508 https://fbt.tums.ac.ir/index.php/fbt/article/download/508/344