Radiation-induced bystander effects: Mechanisms, biological implications, and current investigations at the Leipzig LIPSION facility

The bystander effect is a relatively new area of radiobiological research, which is aimed at studying post-radiation changes in neighboring non-hit cells or tissues. The bystander effect of ionizing irradiation is important after low-dose irradiation in the range of up to 0.2 Gy, where a higher incidence of stochastic damage was observed than was expected from a linear-quadratic model. It is also important when the irradiation of a cell population is highly non-uniform. This review summarizes most of the important results and proposed bystander effect mechanisms as well as their impact on theory and clinical practice. The literature, in parts contradictory, is collected, the main topics are outlined, and some basic papers are described in more detail. In order to illustrate the microbeam technique, which is considered relevant for the bystander effect research, the state of the Leipzig LIPSION nanoprobe facility is described. The resistance of a radiation-induced bystander effect is now generally accepted. The current state of knowledge on it is summarized here. Several groups worldwide are working on understanding its different aspects and its impact on radiobiology and radiation protection. The observation of a bystander effect has posed many questions, and answering them is a challenging topic for radiobiology in the future.