we have load down down the¡¨ ¡§Low Dose Extrapolation of Radiation-Related Cancer Risk¡¨, and have analyzed it carefully. We are not knowledgeable to completely understand all those technical materials in a limited time, yet we realized that there are many conceptual differences to what we learned from the health effects of radiation observed in the residents living in Co-60 contaminated apartments in Taiwan. So that we would like to render some conceptual comments based on the Taiwan incident to the ¡§low-dose extrapolation of radiation-related cancer risk¡¨ to the task group who are establishing a new ICRP recommendation for radiation protection:
1. The health effects of radiation induced to man with the LNT hypothesis was mainly observed from the acute radiation received in extremely high dose rate from the atomic radiation in Japan, no matter how small the doses received would increase cancer mortality. The LNT hypothesis could appropriately apply to radiation in high doses, particularly for leukemia, but when doses <200 mSv, no harmful effects could be obviously observed both for solid cancer and leukemia, the DDREF factors do not mean any thing.
2. The health effects of chronic radiation received in the low dose rate by the residents in the Co-60 contaminated apartments are always beneficial to man, even doses accumulated to high level. When doses in 50-100 mSv/y it might sharply reduce cancer mortality as vaccine to man. The significant data obtained in the Taiwan incident were that the dose rate in 1 mSv/hr ever detected in 1983 in many key positions in the contaminated apartments, such as at sofas in living room, beds in the bedroom, kitchen, study, etc. The average dose received by the residents in first year 1983 was close to 50 mSv/y. The average accumulated dose in 21 years was close to 0.4 Sv, high up to 6 Sv., which is higher than the average individual doses received by atomic bomb survivors in Japan, and the emergency workers in Chernobyl.
3. As the chronic radiation received in the Taiwan Co-60 contamination incident is quite similar to the radiation received by the workers and general public in the peaceful use of nuclear energy and medical application of radiation, so that the policy and practices of radiation protection should not be based on the LNT hypothesis derived from the atomic bomb explosion, but based on the data observed from the Taiwan Co-60 contamination incident, which might constantly benefit the workers and population. The present tentative dose limits are recommended: 1, Radiation in dose rate < 1mSv/hr is nomenclature chronic radiation, 2, 1mSv/hr might be accessed any time any place any where, 3, 50 mSv/y is encouraged to receive by both workers and population, <10 Sv/y might be still beneficial to man, if doses uniformly received in low dose rate.. .
4. The epidemiological methodology for evaluating of the health effects of radiation is appropriate for study of chronic radiation received by workers and population, as the number of natural cancer death of man is quite high, if chronic radiation could really reduce cancers it is easy to observe. The acute radiation could increase cancers, especially to leukemia, the number predicated with the ICRP cancer risk coefficient is so small that is difficult in discerning with the big number of natural or spontaneous cancer deaths. Leukemia could be easily caused by acute radiation, but leukemia is only a small ratio in total cancers, it is still hard to discern from natural cancers. If chronic radiation is believed could reduce cancer deaths, they should be easily observed in a short time, no long latent period involved. That was why the cancer deaths of residents living the contaminated apartments readily observed in the next year right after they moved in the contaminated apartments.
5. We are not qualified to positively assure that the health effects of chronic radiation serendipitously observed are really beneficial to man, we would strongly recommend the international scientists and communities to reexamine or investigate it. And if the health effects of chronic radiation from the Co-60 incident in Taiwan are really beneficial to man, many uncertainty cases of the cancer mortality whether really increase or decrease could be clarified, such as the lower cancer mortality observed in the high natural backgrounds areas as in Yangjing, China. Kerala, India, and Colorado, USA, the population living in higher concentration of radon whether really beneficial to them. And whether the nuclear energy workers in many countries had really lower cancer mortality, and whether the accidents in the nuclear fuel factory in east Urals and in Chernobyl nuclear power plants had highly reduced the cancer mortality of the workers and population.
6. The higher leukemia mortality of the atomic bomb survivors in Japan created the LNT hypothesis and the cancer risk coefficient, which are presently used for estimation of the cancer mortality of nuclear workers, and used as the basic policy for radiation protection. The Co-60 contamination incident in Taiwan might provide a practical way for evaluating the cancer mortality of nuclear workers whether increased or decreased by chronic radiation, and a new approach for radiation protection. The table 6 in 2005 ICRP recommendation suggested a cancer risk coefficient for the adult workers (age in 20-64, with a lower cancer risk coefficient than that of general population) that could be used for estimating the cancer mortality of the nuclear workers and population. According to the national statistics of death causes in Taiwan, the average cancer mortality of Taiwan population in age 20-64 is lower than that of the whole population, but the workers are most male, the cancer mortality of male is about 1.3~1.4 times higher than the whole population. So that if the workers are most male, uniformly in age 20-64, and the mortality has the male and female ratio as in Taiwan, multiply the whole population by 1.3 or 1.4, then the workers would have the same cancer mortality as the whole population, and then to straight compare the mortality of the workers and population, could readily reveal the mortality of the workers whether reduce or increase. So that the US navy Shipyard workers health should be better to compare directly with the cancer mortality of population near the shipyard, not to analysis their leukemia.
7. The radiation health effects data obtained from atomic survivors in Japan was valuable for the radiation protection used until today, but the health effects observed in the Taiwan incident could provide much better data for radiation protection. It deserves an international and thoroughly review the incident in Taiwan, it might be really benefit the peaceful use of nuclear energy, make the public never fear of radiation, and the chronic radiation itself might be an effective method for immunization of cancers. This is why our research group would like to make such humble recommendation based on the Taiwan Co-60 contamination incident to ICRP for hoping the ICRP would initiate a new system for nuclear energy and radiation application.
Y. C Luan Senior Scientist of the Nuclear Science and Technology Association
Consultant of the Nuclear, Biology and Chemical Society in Taiwan.