|In the Japan Radiation Research Society a working group was established to review and discuss the Draft Recommendation of ICRP. Comments on the Draft Recommendation were prepared based on the discussion among the member of the working group.
1. “Deterministic Effects” to “Tissue Reactions”
The substitution of the generic term with more specific term is reasonable to avoid a term not familiar to those outside of the radiological protection. However, “tissue reaction” does not seem to mean adverse effects, which are the concern in the radiological protection. A more appropriate term should be chosen.
In Paragraph (76), the term “risk” is used for the tissue reactions. In ICRP publications “risk” has been used for stochastic effects. Therefore, another term, such as “incidence” should be used here instead of “risk”.
2. “Stochastic Effects” to “Cancers and Heritable Effects”
This substitution is also reasonable to avoid an unfamiliar technical term. However, the single category of “cancer and heritable effects” would give an impression that cancer and heritable effects are of equal significance in the radiological protection. In reality, an increase in cancer risk has been observed in a dose range higher than 100 mSv. On the other hand, the heritable effects have never been observed in human beings. To avoid the confusion, “cancer” and “heritable effects” should be classified into separate categories.
3 . LNT hypothesis
It is understandable to adopt the LNT hypothesis to estimate the potential risks in low dose range, where accurate estimation is essentially impossible due to uncertainties, for the purpose of radiological protection. However, due to the LNT hypothesis the general public tends to believe that ionizing radiation is harmful no matter how low thee dose is. Therefore, the Commission should clearly mention that the LNT hypothesis is a tool for radiological protection and is not a description of the actual risk from ionizing radiation of low doses. In this sense, it is appreciated that the Paragraphs 57,143,and 147 describe the caution for inappropriate use of the LNT hypothesis itself, and effective dose and collective dose, which are based on the LNT hypothesis. In addition to these statements, a caution should be added in the Paragraph 55, where the appropriateness of LNT hypothesis is claimed. Also, in the Paragraph 55, “scientifically reasonable” should be replaced by “practically reasonable” or “operationally reasonable”.
Projection of biological effects of radiation of high doses to low doses and high dos-rate to low dose-rate has been discussed with a single coefficient, DDREF. This is because in the situation where a single cell is traversed by a single track of radiation, a dose effect and a dose-rate effect are supposed to be equivalent. This seems appropriate only when a single cell is considered; Turn over of cells and cell-to-cell interaction taken into consideration, situation should be different; the dose effect and the dose rate effect should be discussed separately.
Furthermore, the concept of DDREF is contradictory to the concept of LNT. If one assumes a linear dose response relationship, DDREF should automatically 1; the Commission should more clearly explain the relationship between DDREF and LNT.
5. Impact of Cancer Susceptibility Genes
If the Commission recognises that variant cancer genes of low penetrance may be sufficiently common (Paragraph 85), it does not seem reasonable to state that “the information available is in sufficient to provide a meaningful quantitative judgement”; because, the common variation should be already included in the estimates which are based on the epidemiological estimation.
6. Non-cancer disease
For the inclusion of the non-cancer diseases in the radiological protection (Paragraph 87), discussion should be made not only on the availability of data, but also on the impact of these diseases on the total detriment, which would be smaller than that of cancer.
7. Radiation Weighting Factors
The radiation weighting factors are given as a continuous function to the energy of neutrons. The energy dependence of photons should also be considered, because low energy X-rays, which have been used for in medical and dental diagnosis, show higher RBE.
8. Styles and Structure
Throughout the text of the Recommendation, the Appendices are referred many times. In these cases, not only the Appendix A or B, but also sections, pages, or lines in the Appendices should be cited. In some cases it should be helpful to summarise the description of the referred section. For instance, in Paragraph 49, a brief description of the reasons why the deterministic effect is inappropriate would help the reader understand the argument.
The Recommendation should be the worldwide principle of the radiological protection. It would be translated into many languages. The English language should be as simple as possible and plain words/expression should be used.
The Working Group for Comments on the Draft Recommendation of ICRP
Kazuo Sakai: National Institute of Radiological Sciences
Seiji Kodama: Osaka Prefecture University
Nobuhiko Ban: Oita University of Nursing and Health Sciences
Akinori Yokoya: Japan Atomic Energy Agency