dose-threshold analysis indicated no threshold - zero dose the best estimate of threshold [View all]

[kristopher]

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.

http://www.ncbi.nlm.nih.gov/pubmed/22171960

The gray (symbol: Gy) is the SI derived unit of absorbed radiation dose of ionizing radiation (for example, X-rays), and is defined as the absorption of one joule of ionizing radiation by one kilogram of matter (usually human tissue).[1]
Named after the British physicist Louis Harold Gray, the SI unit replaces the traditional cgs unit, the rad (equivalent to 0.01 Gy), which remains common in industry in the United States, while "strongly discouraged" in the style guide for U.S. National Institute of Standards and Technology authors.[2]

http://en.wikipedia.org/wiki/Gray_(unit)

Paper published by Radiation Research* Studies of the Mortality of Atomic Bomb Survivors, Report 14, 1950–2003: An
Overview of Cancer and Noncancer Diseases

[Findings of this study]
We followed the Life Span Study cohort during the period from 1950 through 2003 and elucidated effects of A-bomb radiation on mortality and causes of death using the DS02 dosimetry system. Excess relative risk (ERR) for all solid cancer mortality showed a linear dose-response relationship over the entire dose range, with no threshold observed, with the lowest dose range with significant risk for all solid cancers 0 to 0.20 Gy. The risk of all solid cancer mortality at the age of 70 years after exposure to 1 Gy at age 30 was 42% higher than that for unexposed individuals, increasing by about 29% per decade decrease in age at exposure. With regard to site-specific cancers, significant increase in cancer risk was observed for stomach, lung, liver, colon, breast, gallbladder, esophagus, bladder, and ovary, whereas rectum, pancreas, uterus, prostate, and kidney parenchyma did not have significantly increased risk. Increased risks of non-cancer diseases including those of the circulatory, respiratory and digestive systems were observed, but whether there was a causal relationship with radiation requires further investigation.

[Explanations]

1) This report covers an additional six years of follow-up since the 13th LSS report was published in 2003. This is the first time the DS02 dosimetry system has been used for estimating individual dose and comprehensively analyzing radiation risk by cause of death. The subject population consisted of 86,611 directly exposed A-bomb survivors with individual dose estimates available, from among the LSS cohort of about 120,000 people. During the follow-up period, 50,620 people died, a number representing 58% of the original population, including 10,929 solid cancer deaths.

2) ERR* at the age of 70 years after exposure at age 30 was 0.42/Gy (95% confidence interval [CI]: 0.32, 0.53), while excess absolute risk** was 26.4 persons/Gy /10,000 person-year.

3) Excess cancer deaths attributable to radiation exposure are estimated to account for more than half of all solid cancer deaths in the dose range of 2 Gy or greater, with the same being the case for about one-fourth in the range of 0.5 Gy-1 Gy and about one-twentieth in the range of 0.1-0.2 Gy.

4) The linear dose-response relationship provided the best fit for the ERR data across the entire dose range, but a concave curve was the best fit for data restricted to dose < 2 Gy. This resulted because risk estimates for exposure to around 0.5 Gy were lower than those in the linear model.

The Radiation Effects Research Foundation has studied A-bomb survivors in Hiroshima and Nagasaki for more than 60 years. RERF’s research achievements are considered the principal scientific basis for assessment of radiation risk by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and recommendations regarding radiation protection standards by the International Commission on Radiological Protection (ICRP).
Radiation Research, the official monthly journal of the US Radiation Research Society, publishes original and review articles dealing with radiation effects and related subjects in the areas of physics, chemistry, biology and medicine (impact factor in 2010: 2.578).