The ICRP’s System of radiological protection has been changing over time, and while it is robust enough, there is a need to add new knowledge and further improvement. Radiological protection is based on a combination of scientific knowledge, experience, and values; however, experience and values would be flexible and change with time and region. Radiation biology strives for universality based on biological mechanisms. At low dose and low dose rate, which is the main area of radiation protection, carcinogenesis is regarded as the main risk and its knowledge need to be elucidated. The DDREF is considered separately as LDEF and DREF nowadays. The key question is how to apply them to radiation risk inference. In terms of risk estimation by epidemiology, the paper of an extended observation period for cancer incidence for high natural radiation areas in Kerala, India, is recently published. It shows that there is no increase in cancer risk with increasing cumulative dose with greater confidence. The involvement of stem cell competition, as proposed in ICRP Publ. 131, in the dose rate effect has also been clarified by recent biological studies. On the other hand, in the implementation of the system of radiological protection, it is necessary to clearly show how to deal with uncertainty when protection measures are taken for small doses. It would be a departure from the principle of optimisation to require additional conservatism based on the precautionary principle when radiation safety standards established with sufficiently conservative assumptions are complied with. Another important issue for the application of optimisation will be waste management, which requires different actions depending on the exposure situation; although there is very little on waste management in the ICRP papers, it is necessary to discuss whether the guidance in the existing publications should be basically effective or not. The concept of waste disposal in existing exposure situations could be a point of discussion. Although, it is understandable that simplification and clarification are useful for the application of protection, due consideration should be taken to avoid misunderstanding and confusion. It is hoped that the process of reaching a decision on the basic approach and arrangements for the System of RP will be carried out with open doors involving stakeholders.
Keywords: low dose and low dose rate; carcinogenesis; risk inference; application of optimization
Thanks, Michiya, for your presentation. In particular, I appreciate that you pointed out that RP in waste management is an area that might need to be reviewed, something which we did not mention in the 'Fit for Purpose' paper. I look forward to hearing from CRIEPI and others what aspects might need attention.
I also appreciate your caution about simplification. Clarification is important, and some simplification may help achieve this, but as you say we must also avoid misunderstanding and confusion. In addition, the System needs to handle complex and unforeseen problems, so oversimplification should be avoided. This will be a challenge!