Radiation Effects Research Foundation (RERF) is the successor organization of the Atomic Bomb Casualty Commission (ABCC) to conduct investigations of the late effects of radiation among the atomic-bomb survivors in Hiroshima and Nagasaki.
In its 14th report on mortality in the Life Span Study (LSS) cohort of atomic bomb survivors published in March this year in the "Radiation Research" magazine, the official journal of the US Radiation Research Society, the researchers at RERF say there was no "threshold":
Importantly, for solid cancers the additive radiation risk (i.e., excess cancer cases per 104 person-years per Gy) continues to increase throughout life with a linear dose–response relationship.
The estimated lowest dose range with a significant ERR [excess relative risk] for all solid cancer was 0 to 0.20 Gy, and a formal dose-threshold analysis indicated no threshold; i.e., zero dose was the best estimate of the threshold.
According to the blogger who posted the link to the paper says he/she called the Ministry of Health and Welfare on May 1 and asked: "Ministry of Health and Ministry of Foreign Affairs oversee the RERF. I understand from this report that it has now been epidemiologically proven that even a low-dose radiation exposure resulted in negative health effect such as dose-dependent increase in cancer. This is contrary to the position of the Japanese government which is based on the IRCP assertion that there is no epidemiological proof that there is a health risk in low-dose radiation exposure but the radiation protection standards are set assuming there is such a risk. Is there any press release planned by the Ministry of Health? Is my understanding correct?" The answer from the official in charge at the Ministry was, according to him/her, "Your understanding is correct. The Ministry doesn't have a plan for any press release, because the RERF has already done so."
There is hardly any coverage of this paper by the mainstream media in Japan.
While the RERF continues to study (and not treat) the effect of atomic bombs on human health, there is a worthy successor in Fukushima Medical University, headed by Dr. Shunichi Yamashita. He has been mostly quite successful in convincing the residents in Fukushima Prefecture to continue to live in Fukushima. That gives him close to 2 million subjects to study. By the way, Dr. Yamashita's stance is that "unless you are exposed to radiation at 100 millisieverts or more in a single episode, there is no increase in cancer risks". Well the RERF study seems to finally disprove that.
The abstract part of the paper by Ozasa, K., Shimizu, Y., Suyama, A., Kasagi, F., Soda, M., Grant, E. J., Sakata, R., Sugiyama, H. and Kodama, K. "Studies of the Mortality of Atomic Bomb Survivors, Report 14, 1950–2003: An Overview of Cancer and Noncancer Diseases. Radiat. Res. 177, 229–243 (2012)":
This is the 14th report in a series of periodic general reports on mortality in the Life Span Study (LSS) cohort of atomic bomb survivors followed by the Radiation Effects Research Foundation to investigate the late health effects of the radiation from the atomic bombs. During the period 1950–2003, 58% of the 86,611 LSS cohort members with DS02 dose estimates have died. The 6 years of additional follow-up since the previous report provide substantially more information at longer periods after radiation exposure (17% more cancer deaths), especially among those under age 10 at exposure (58% more deaths). Poisson regression methods were used to investigate the magnitude of the radiation-associated risks, the shape of the dose response, and effect modification by gender, age at exposure, and attained age. The risk of all causes of death was positively associated with radiation dose. Importantly, for solid cancers the additive radiation risk (i.e., excess cancer cases per 104 person-years per Gy) continues to increase throughout life with a linear dose–response relationship. The sex-averaged excess relative risk per Gy was 0.42 [95% confidence interval (CI): 0.32, 0.53] for all solid cancer at age 70 years after exposure at age 30 based on a linear model. The risk increased by about 29% per decade decrease in age at exposure (95% CI: 17%, 41%). The estimated lowest dose range with a significant ERR for all solid cancer was 0 to 0.20 Gy, and a formal dose-threshold analysis indicated no threshold; i.e., zero dose was the best estimate of the threshold. The risk of cancer mortality increased significantly for most major sites, including stomach, lung, liver, colon, breast, gallbladder, esophagus, bladder and ovary, whereas rectum, pancreas, uterus, prostate and kidney parenchyma did not have significantly increased risks. An increased risk of non-neoplastic diseases including the circulatory, respiratory and digestive systems was observed, but whether these are causal relationships requires further investigation. There was no evidence of a radiation effect for infectious or external causes of death.