Health risks attributable to radiation

Draft document: Health risks attributable to radiation
Submitted by Keij Oda, Faculty of Maritime Science, Kobe University
Commenting as an individual

Comments on the ICRP foundation document draft: "Health Risks Attributable to Radiation" has been reviewed by Working Group of International Issues, the Japan Health Physics Society 1. The LNT Hypothesis (p.5, Lines.188~190 / pp.58~60, Chapter4, 4.4.5) It should be appreciated that the Document states that the LNT hypothesis is for the purposes of radiological protection, due to the uncertainty associated with the estimation of the risk from low dose/dose-rate irradiation. A fear or unreasonable concern about low level radiation/radioactivity of general public is based on the LNT hypothesis; the statement of ICRP that the LNT hypothesis is only for the purpose of radiological protection and does not necessarily reflect the actual effect of very low dose would reduce the anxiety of the public. However, in this regard, the statement that the use of LNT hypothesis is a gscientifically plausible assumptionh (p.5, Lines 188~190) may be misleading. gPracticalh rather than gscientifically plausibleh should be used. 2. Dose related to tissue injury (p.28 Chapter 3, Section 3.1.7) It is discussed whether to apply equivalent dose (Sv) or radiation weighted dose (Gy) as the dose to express dose limits for specific tissues (p28, Chapter 3). The use of equivalent dose is recommended. However, there seems to be confusion regarding the name of the dose unit. Radiation weighting factors for calculating the equivalent dose from the absorbed dose is a factor intended for low-dose stochastic effects. Therefore, it should not be used for the dose limits regarding tissue injury. It should be confusing to use gGyh for both radiation-weighted dose and absorbed dose. A name of the unit of the dose gGy-Eqh was proposed in the draft 2005 Recommendations; this name may be appropriate. 3. Source of Epidemiological Data for estimating the human risk (pp.40~, Chapter 4, Section 4.4) It is appreciated that the Committee 1 considered epidemiological data on medical exposure, occupational exposure, and environmental exposure as well as A-bomb survivors. However, we have another set of data which should be taken into consideration from research on health effects of those living in high natural background radiation area. The strength of these data are as follows; (1) they cover both males and females, (2) they cover all ages, (3) the exposure is protracted one at low dose rate, (4) the exposure was under non-stressful situation compared to medical exposures and A-bomb survivors. These data have accumulated and a number of qualified papers have been published to demonstrate that there was no increase in cancer mortality in those areas where the natural background radiation is 3 times as high as the average (J. Radiat. Res., 41 Suppl., 31-41, 2000). 4. Change in the tissue weighting factors (p.56, Chapter 4, Table 4.3) The tissue weighting factor has been changed from 0.2 to 0.08 and 0.05 to 0.08 for the gonad and the breast, respectively. In the draft 2005 recommendation, however, it was 0.05 for the gonad and 0.12 for the breast. The explanation for the change given in the draft 2005 recommendation was reasonable: the decreased contribution of hereditary effects and the increased contribution of breast cancer in the detriment. Detailed explanation should be necessary for the further change of the tissue weighting factors. 5. Hereditary Effect (p.76, Chapter 6) Historically, the hereditary effects were one of the greatest concerns in radiological protection. However, under the situation that no hereditary effect has been detected in human beings, it should not be reasonable to estimate the risk based on the spontaneous mutation rate in humans and the doubling dose obtained from animal experiments. Assessing the hereditary risk in this way seem not in accordance with the conclusion that gEven in the absence of a true dose-threshold, any effects on IQ following in-utero doses of a few tens of mGy would be undetectable and therefore of no practical significanceh (Lines 1211-1213, p29). The Committee could mention that there is gno practical significanceh in the hereditary effects for low dose/dose-rate radiation, while the historical review on the hereditary effects would be very informative. 6. Table7.1 (pp.102~103) This table is concise summary of the present Document. If the differences in the conclusions or numerical judgements from those in the previous recommendations are listed, it would be more informative.