In 1982, several Co-60 sources were accidentally recycled by the steel scrap industry in northern Taiwan and resulted in contaminated steel products that were used to construct many apartment buildings. The residents of the apartment buildings received exposure to low-level radiation due to the contaminated steel in the buildings for many years.
A few reports have been published regarding the cancer rates in this population group.
The first report by Hwang et al. (Hwang et al., 2006), reported that the standardized incidence ratio (SIR) for all cancers (for males and females) of the irradiated population was reduced, in comparison to an age-gender matched Taiwanese population (see Part of Table III shown below):
In two later reports on the same cohort, (Hwang et al., 2008) and (Hsieh et al., 2017), the authors reported that some additional cancers were observed with the increased follow-up in the population group. However, instead of comparing the cancer rates in the irradiated group with the age-sex matched control population in Taiwan, as was done in the 2006 report, they fitted the incidence data for a few cancers as a function of radiation dose and concluded that there was increased risk for a few cancer types following low radiation exposures in this population group. The problem with this approach is that there would be large statistical errors because of the poor statistics when individual cancers are considered. Statistical fluctuations can make a few cancers have statistically significant increase in the irradiated population, and so results of such analysis can be misleading. When there are poor statistics, an analysis that includes all cancers has the best chance of providing a valid conclusion.
An analysis of the additional cancer data presented in these two publications has been performed to estimate the SIR in the irradiated population group (Doss, 2018).
Based on the data presented in (Hwang et al., 2008), the number of observed cancer cases is 95. The expected cancer cases up to the end of 2002 has been estimated to be 114.9, resulting in a SIR for all cancers of 0.83 (95% CI: 0.66–0.99).
For the data presented in (Hsieh et al., 2017), the number of observed cancer cases is 246. The expected cancer cases up to the end of 2012 has been estimated to be 296.4, resulting in a SIR for all cancers of 0.84 (95% CI: 0.74–0.95).
Thus, the reduction of cancer rate reported for the irradiated population in (Hwang et al., 2006) publication is observed to be present in the later updates also. These data are consistent with radiation hormesis and contradict the LNT model.
References
DOSS, M. Comment on '30 years follow-up and increased risks of breast cancer and leukaemia after long-term low-dose-rate radiation exposure'. Br J Cancer, v. 118, n. 5, p. e9, Mar 6 2018. https://www.ncbi.nlm.nih.gov/pubmed/29438374
HSIEH, W. H. et al. 30 years follow-up and increased risks of breast cancer and leukaemia after long-term low-dose-rate radiation exposure. Br J Cancer, v. 117, n. 12, p. 1883-1887, Dec 5 2017. https://www.ncbi.nlm.nih.gov/pubmed/28972968
HWANG, S. L. et al. Cancer risks in a population with prolonged low dose-rate gamma-radiation exposure in radiocontaminated buildings, 1983-2002. Int J Radiat Biol, v. 82, n. 12, p. 849-58, Dec 2006. http://www.ncbi.nlm.nih.gov/pubmed/17178625
HWANG, S. L. et al. 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 Res, v. 170, n. 2, p. 143-8, Aug 2008. http://www.ncbi.nlm.nih.gov/pubmed/18666807