WNA response to ICRP Consultation on Stem Cell Biology with Respect to Carcinogenesis Aspects of Radiological Protection
The WNA recognises that a robust system for radiological protection relies on firm scientific basis, and that substantial efforts are being made to reduce the many scientific uncertainties relating to the impacts of radiation dose. As part of the demonstration of valid results, it is clear that the scientific community needs to ensure that the results gathered from carefully prepared epidemiological studies are consistent with the results of biological studies on mechanisms. The WNA welcomes this report as it provides a comprehensive review of advances in the knowledge of the biology and radiation response of stem cells in relation to important issues within radiation protection.
This report indicates that there are three levels of quality control systems in a body to maintain genomic integrity; the molecular-level quality control of DNA repair, the cellular-level quality control of apoptosis, and the tissue level quality control of stem cell competition. Looking at the tissue-based considerations, it suggests that the dose effectiveness factor (DEF) and dose rate effectiveness factor (DREF) are conceptually different at the biological level, even though it is captured as a single numerical value for the dose and dose rate effectiveness factor (DDREF). At this level, this report suggests the possibility that the concept of competition between normal and radiation-injured stem cells may result in lower carcinogenic events when doses are provided at low dose rate (similar to Kerala in India), compared with the information after high dose rate irradiation (mainly from epidemiological study of A-bomb survivors). In terms of the relationship between biological mechanisms and epidemiological studies, it suggests that more emphasis should be given to low chronic epidemiological data rather than relying on risk projections from acute higher dose data.
The WNA believes that although the scientific information contained in this present report is not fully conclusive, it begins to clarify the future direction of epidemiological and biological research relevant to risk assessment, and evolution of the existing RP system. In this light, this report is deemed an important document. Further research and discussions within the scientific community would be welcomed on this topic.