Low dose radiation and cancer in A-bomb survivors: latency and non-linear dose-response in the 1950-90 mortality cohort.
BACKGROUND
Analyses of Japanese A-bomb survivors' cancer mortality risks are used to establish recommended annual dose limits, currently set at 1 mSv (public) and 20 mSv (occupational). Do radiation doses below 20 mSv have significant impact on cancer mortality in Japanese A-bomb survivors, and is the dose-response linear?


METHODS
I analyse stomach, liver, lung, colon, uterus, and all-solid cancer mortality in the 0-20 mSv colon dose subcohort of the 1950-90 (grouped) mortality cohort, by Poisson regression using a time-lagged colon dose to detect latency, while controlling for gender, attained age, and age-at-exposure. I compare linear and non-linear models, including one adapted from the cellular bystander effect for alpha particles.


RESULTS
With a lagged linear model, Excess Relative Risk (ERR) for the liver and all-solid cancers is significantly positive and several orders of magnitude above extrapolations from the Life Span Study Report 12 analysis of the full cohort. Non-linear models are strongly superior to the linear model for the stomach (latency 11.89 years), liver (36.90), lung (13.60) and all-solid (43.86) in fitting the 0-20 mSv data and show significant positive ERR at 0.25 mSv and 10 mSv lagged dose. The slope of the dose-response near zero is several orders of magnitude above the slope at high doses.


CONCLUSIONS
The standard linear model applied to the full 1950-90 cohort greatly underestimates the risks at low doses, which are significant when the 0-20 mSv subcohort is modelled with latency. Non-linear models give a much better fit and are compatible with a bystander effect.
Dropkin
Greg
G
Flat 5, 32 Sheil Rd, Liverpool L6 3AE, UK. gregd@gn.apc.org
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D007223:Infant; D007564:Japan; D008297:Male; D008875:Middle Aged; D009381:Neoplasms, Radiation-Induced / Q000401:mortality*; D009689:Nuclear Warfare; D012044:Regression Analysis; D012307:Risk Factors; D017741:Survivors; D013997:Time Factors; D047789:World War II