Radiation-induced bystander effect following hypo- fraction technique of grid therapy by use of sensitive molecular markers

Introduction: Radiation-induced bystander effect (RIBE) is a well-known response associated with the induction of radiation effects in non-irradiated cells via signaling of hit ones. As this so-called phenomenon has been largely investigated in low dose levels, few studies focused on higher dose levels such as grid therapy. Grid therapy or spatially fractionated grid radiation therapy (SFGRT) is a hypo-fraction technique for treatment of advance and bulky malignant tumors. Different advantages of SFGRT including minimal skin side effects and effective tumor control despite the small portion of exposure based on grid pattern, made it as an attractive therapy approach. SO the aim of this research was determination of bystander response following the mentioned therapy method. Materials and Methods: In this study, we evaluated RIBE via distinct protocols of media transfer and cell to cell contact following grid therapy. Two different human cell lines (SCC and Hela) were irradiated by challenging dose of ۱۰ Gy with available grid block attached to the linac head in single radiation field. Irradiation with Grid pattern of ۱۴۵ circular fields, ۱۳mm in diameter with ۱۷mm center to center distance created the cell to cell contact of directly irradiated and bystander cells. To fulfill the aim of media transfer of our study, bystander cells or grid adjacent cells were irradiated by ۱.۵Gy receiving the conditioned medium of hit cells. Based on RIBE DNA damage and DSB formation, phosphorylation of histone H۲AX could be the novel sensitive marker for early detection of DSBs in intact cells. So Bystander effect has been assessed by use of sensitive molecular biomarkers of gamma h۲ax as well as gene expression. Results& Conclusion: Our results indicated the occurrence of RIBE following the high dose hypo-fraction technique of grid therapy and emphasized on the role of sensitive molecular biomarkers in bystander DNA damage mechanism.