Abstract
Accumulating evidence indicates that the biological effects of low-dose and low-dose-rate radiation are different from those of high-dose and high-dose-rate radiation. Radiation-induced bystander response is defined as a radiation-induced response in cells that have not been directly targeted by radiation but have been in the neighborhood of cells that have been directly exposed to radiation. Therefore, it is important to elucidate the bystander response to evaluate the risk of low-dose radiation. Many studies have reported bystander responses induced by high-linear energy transfer (LET) charged particle radiations. However, few studies have reported the effects of low-LET photons.
The microbeam X-ray irradiation system at the Central Research Institute of Electric Power Industry (CRIEPI) is a powerful tool to investigate the cellular response to low-dose and low-dose-rate radiation. This X-ray microbeam irradiation system was developed in March 2007. Our system is characterized by a tabletop X-ray focusing system that uses a Fresnel zone plate (FZP), and an on-line confocal laser microscope. A characteristic X-ray of aluminum (1.49 keV) was generated by focused electron bombardment on an aluminum target. The FZP is designed to focus aluminum K-shell X-rays. The diameter of the X-ray beam is 2–3 microns.
Using our irradiation system, 5 cell nuclei in confluent normal human WI-38 cells were irradiated with X-ray microbeams. It was found that the bystander cell-killing effect showed a parabolic relationship with the irradiation dose. In addition, nitric oxide was shown to be a strong candidate for the initiation/mediation of the bystander response induced by soft X-rays. Recent developments in our system are presented in our poster.
