[ RadSafe ] Update on cancer risks due to Co-60 in Taiwanese dwellings

[Monty Charles]

About 3 years ago there was considerable interest in a preliminary 
study of health effects in a Taiwanese cohort of people exposed in 
their homes in Taiwan as a result of Co-60 in the steel structure of 
dwellings.  The initial findings, presented at a Health Physics Society 
meeting, appeared to indicate a cancer deficit.  Considerable interest 
was shown in this study and the Health Physics Society formally 
called for further follow up. A subsequent study which now meets 
conventional epidemiological requirements has now been published 
and concludes - 'The results suggest that prolonged low dose-rate 
radiation exposure appeared to increase risks of developing certain 
cancers in specific subgroups of this population in Taiwan'.

Monty Charles
************************
Volume 82 Number 12/December 2006 of International Journal of 
Radiation Biology. URL of article:
http://journalsonline.tandf.co.uk/link.asp?id=V8662J8R606731L3

Cancer risks in a population with prolonged low dose-rate gamma-
radiation exposure in radiocontaminated buildings,1983-2002, p. 
849	
S. -L. Hwang, H. -R. Guo, W. -A. Hsieh, J. -S. Hwang, S. -D.
Lee, J. -L. Tang, C. -C. Chen, T. -C. Chang, J. -D. Wang, W.
P. Chang
Abstract: 
Purpose: To assess cancer risks in a population that received 
prolonged low dose-rate -irradiation for about 10 years as a result of 
occupying buildings containing 60Co-contaminated steel in Taiwan.
Materials and methods: The cancer risks were compared with those 
populations with the same temporal and geographic characteristics in 
Taiwan by standardized incidence ratios (SIR), adjusted for age and 
gender. The association of cancer risks with excess cumulative 
exposure was further evaluated for their relative risks by the Poisson 
multiple regression analysis.
Result: A total of 7271 people were registered as the exposed 
population, with 101,560 person-years at risk. The average excess 
cumulative exposure was approximately 47.8mSv 
(range<1-2,363mSv). A total of 141 exposed subjects with various 
cancers were observed, while 95 developed leukemia or solid cancers 
after more than 2 or 10 years initial residence in contaminated 
buildings respectively. The SIR were significantly higher for all 
leukemia except chronic lymphocytic leukemia (n=6, SIR=3.6, 
95% confidence interval [CI] 1.2-7.4) in men, and marginally 
significant for thyroid cancers (n=6, SIR=2.6, 95% CI 1.0-5.7) in 
women. On the other hand, all cancers combined, all solid cancers 
combined were shown to exhibit significant exposure-dependent 
increased risks in individuals with the initial exposure before the age 
of 30, but not beyond this age.
Conclusions: The results suggest that prolonged low dose-rate 
radiation exposure appeared to increase risks of developing certain 
cancers in specific subgroups of this population in Taiwan.
********************************************

Dr Monty Charles
Reader in Radiation Physics
Head of Radiation Biophysics
Coordinator of Taught Postgraduate Courses
School of Physics & Astronomy
University of Birmingham
Birmingham B15 2TT
Tel +44 (0)121 414 3483