Radiation-Induced Rescue Effect: Insights from Microbeam Experiments

SIMPLE SUMMARY: The present paper introduces a radiobiological phenomenon known as the Radiation-Induced Rescue Effect (RIRE), where the radiobiological effects developed in cells irradiated with ionizing radiations are mitigated by non-irradiated cells. The primary objective of a radiotherapy treatment is to kill cancer cells with ionizing radiation while at the same time sparing the normal cells. However, RIRE was found capable of saving some of the irradiated cancer cells, so the efficacy and outcome of radiotherapy might be undermined. As such, it would be pertinent to have a better understanding of RIRE, including its underlying mechanisms and its relationships with other non-traditional radiobiological phenomena. Microbeam irradiations have some unique features that could help research on RIRE, which are explained. The paper also reviews the insights gained from previous microbeam experiments on RIRE. Some thoughts on future priorities and directions of research on RIRE exploiting unique features of microbeam radiations are presented in the last section. ABSTRACT: The present paper reviews a non-targeted effect in radiobiology known as the Radiation-Induced Rescue Effect (RIRE) and insights gained from previous microbeam experiments on RIRE. RIRE describes the mitigation of radiobiological effects in targeted irradiated cells after they receive feedback signals from co-cultured non-irradiated bystander cells, or from the medium previously conditioning those co-cultured non-irradiated bystander cells. RIRE has established or has the potential of establishing relationships with other non-traditional new developments in the fields of radiobiology, including Radiation-Induced Bystander Effect (RIBE), Radiation-Induced Field Size Effect (RIFSE) and ultra-high dose rate (FLASH) effect, which are explained. The paper first introduces RIRE, summarizes previous findings, and surveys the mechanisms proposed for observations. Unique opportunities offered by microbeam irradiations for RIRE research and some previous microbeam studies on RIRE are then described. Some thoughts on future priorities and directions of research on RIRE exploiting unique features of microbeam radiations are presented in the last section.