Estimates of relative risks for cancers in a population after prolonged low-dose-rate radiation exposure: a follow-up assessment from 1983 to 2005.

Radiation effects on cancer risks in a cohort of Taiwanese residents who received protracted low-dose-rate gamma-radiation exposures from (60)Co-contaminated reinforcing steel used to build their apartments were studied, and risks were compared to those in other radiation-exposed cohorts. Analyses were based on a more extended follow-up of the cohort population in which 117 cancer cases diagnosed between 1983 and 2005 among 6,242 people with an average excess cumulative exposure estimate of about 48 mGy. Cases were identified from Taiwan's National Cancer Registry. Radiation effects on cancer risk were estimated using proportional hazards models and were summarized in terms of the hazard ratio associated with a 100-mGy increase in dose (HR(100mGy)). A significant radiation risk was observed for leukemia excluding chronic lymphocytic leukemia (HR(100mGy) 1.19, 90% CI 1.01-1.31). Breast cancer exhibited a marginally significant dose response (HR(100mGy) 1.12, 90% CI 0.99-1.21). The results further strengthen the association between protracted low-dose radiation and cancer risks, especially for breast cancers and leukemia, in this unique cohort population.

Evaluation of the frequencies of chromosomal aberrations in a population exposed to prolonged low dose-rate 60Co gamma-irradiation.

PURPOSE: Chromosomal aberration analysis in peripheral blood lymphocytes was performed to evaluate late cytogenetic effects of long-term low dose-rate gamma-irradiation exposure among students and residents exposed in radiocontaminated buildings. MATERIALS AND METHODS: Blood samples were taken from 1913 subjects (age 17.8+/-13.6, mean+/-SD) 5-8 years after their relocation from radioactive environments as well as from 176 non-exposed subjects (age 29.6+/-11.9) from the local community. Their lymphocytes were cultured for 48 h and metaphase spreads were prepared. A total of 208 900 metaphases were analysed for different types of chromosomal aberrations. RESULTS: Relatively higher frequencies of translocations (2.1 x 10(-3)), rings (0.6 x 10(-3)) and dicentrics (0.6 x 10(-3)) were noted in the exposed population as compared with the nonexposed reference populations. Moreover, 356 (78.6%) of the 453 inversions were found on 14q11.2q32 in the exposed population. Among 392 well-demonstrated translocations, 167 (42.6%) and 175 (44.6%) occurred in chromosomes 7 and 14, respectively, while 139 (35.5%) occurred as t(7;14). In particular, the aberrations t(7;14)(p13;q11.2), t(7;14)(p15;q11.2) and t(7;14)(q36;q11.2) were the most prevalent, occurring with frequencies of 19 (13.7%), 20 (14.4%) and 27 (19.4%), respectively. In these, 3205 breakpoints were documented, with chromosomes 7, 9 and 14 shown to carry significantly higher frequencies of breakpoints than expected (chi(2)-test, p<0.0001). A further six hotspots were identified on 7p15 (57, 1.8%), 7q36 (42, 1.3%), 9q12 (244, 7.6%), 9q13 (86, 2.7%), 14q11.2 (509, 15.9%) and 14q32 (387, 12.1%) in the exposed population. CONCLUSION: In comparison with the unexposed population, we observed increased frequencies of various chromosomal aberrations in this human population with previous exposure to prolonged low dose-rate gamma-radiation. Moreover, several hotspot breakpoints and inversions and translocations were observed on chromosomes 7 and 14.