RADIATION INCDUCED BYSTANDER EFFECT

Abstract

Introduction: Radiation effects observed in cells that are not irradiated are known as non-targeted effects. Radiation induced bystander effect (RIBE) as a kind of non-targeted effect has been introduced in recent years. RIBE occurs in unexposed cells which are related to adjacent or distant irradiated cells. RIBE contradict with target theory which necessitates radiation traversal through the nucleus for affecting cells. Methods: To understand this phenomenon, some investigations and review articles which deal with this subject were studied. Most investigators have applied in vitro experimental methods to investigate RIBE in animal or human cells, but in vivo experiments are also increased in recent years. Results: Both low and high LET radiation cause RIBE. Cell responses to RIBE are including: cell death, chromosomal damage, mutagenesis, neoplastic transformation, genomic instability, cell cycle delay, modification of gene expression and radiosensitivity alteration. At low doses that only some cells are irradiated this phenomenon is significant. However RIBE exists at high doses, due to predomination of direct radiation effects it is less considered. There is link between RIBE and other non-targeted effects such as adaption and genomic instability. Conclusion: At low doses, there is no linear relationship between outcome and the number of cells hit by radiation. Thus this will affect the basic principle of defining dose limits which have been initiated by linear no threshold curve. There is a scope to exploit RIBE in radiotherapy, and also it is important to avoid undesirable bystander effects in normal tissues.