27.Adaptation to Low-Dose Ionizing Radiation: Usefulness in Human Health

摘要

Ionizing radiations are integral part of our life. All living organisms exist in a sea of ionizing radiations showered from cosmic, telluric and internal sources. It was initially thought that very low radiation dose, even to the extent of a single hit, was harmful to the biological system (the so-called linear no-threshold (LNT) hypothesis). However, epidemiological studies show prevalence of low cancer incidents in inhabitants residing in high radiation background areas and radiation occupational workers. Furthermore, the results from various animal experiments cast doubt on this LNT theory especially at doses below 50mSv. Interestingly, the recent genomic, cellular, animal and human data have shown that exposure to low-dose whole body irradiation (LD-WBI) appears to stimulate positive cellular and genomic adaptations like activation of immune functions, antioxidant defense system, DNA repair mechanisms, induction of apoptosis etc. These adaptive responses are considered to be beneficial in the amelioration of various reactive oxygen spices (ROS) and immune deficiency related diseases and also useful in effective cancer prevention. Repeated exposure to LD-WBI with gamma-radiation has been in use in the clinical"treatment of lymphomatous malignancies like chronic lymphocytic leukemia (C?L) and non-Hodgkin's lymphoma (NHL) in patients with long term remissions in majority of the cases. The use of LD-WBI thus appears to be an effective new treatment modality in prevention and cure of certain diseases. This review brings in focus the current epidemiological and experimental data related to the clinical aspects of adaptation to low-dose radiation.