An Analysis of Cancer Incidence in Taiwan Apartment Residents Subjected to Low Dose Radiation

Misleading Conclusion in Taiwan Apartment Dwellers Study

In 1982, a number of buildings were constructed in Taiwan using steel unknowingly contaminated with Co-60, exposing thousands of residents to low dose radiation for a number of years.  The health of this group has been monitored and the results have been presented in a couple of papers (Hwang et al., 2006; Hwang et al., 2008).

 The Abstract of (Hwang et al., 2006) presents the results and conclusion thus:

The Abstract of (Hwang et al., 2008) mentions the following conclusion.

On reading these abstracts, it becomes clear that radiation dose of ~50 mSv increases the risk of cancer.  Let us now examine the data presented in these papers to see if such a conclusion is supported by the data.

The paper (Hwang et al., 2006) compared the cancer incidence among the radiated residents of Taiwan apartments with an equivalent matched cohort from Taiwan and determined the Standardized Incidence Ratios (SIRs) for cancer. The SIRs for the exposed population are summarized in Table III on page 854 of the paper. 

Whereas the most significant result (with most statistics) was that the overall cancer rate (or solid cancer rate) was significantly lower in the radiated population, the abstract does not even mention it! By slicing the data into smaller subgroups (with poorer statistics), the authors pointed out in the abstract whenever the cancer rates were elevated. 

In the follow-up paper (Hwang et al 2008), SIRs are no longer calculated and shown, but the LNT model is assumed, and a proportional hazards model is used to calculate excess risk of cancer from the low dose radiation. Let us now analyze the results in some detail to see if the observed reduction of cancers in Hwang 2006 paper continues in the data of Hwang 2008 paper.

On page 852 of  (Hwang et al., 2006) it says:

The average age at the end of the follow-up period was therefore: 17.2 + 16.1 = 33.3

On page 852 of  (Hwang et al., 2006) it says:

In Page 144 of the follow-up paper (Hwang et al., 2008) it says:

In three more years (end of 2002 to end of 2005), average age of the cohort would be 36.3.

Let us now estimate the Expected Cancer incidence in the cohort after 3 additional years of follow up.

 To do this, cancer incidence numbers for age groups in 5 year intervals was obtained from Taiwan Cancer Registry:

      http://tcr.cph.ntu.edu.tw/uploadimages/CI5_V9_Site_e.pdf

The average of male and female cancer incidence on the 20- to 45- range was fitted to an exponential function of age, and the cancer incidence for age of 33.3 and 36.3 was calculated, using the fit.

Cancer incidence rates per 100,000 in Taiwan, using above table from Taiwan cancer registry:
Age Group	20-	25-	30-	35-	40-	45-
Mean Age	22.5	27.5	32.5	37.5	42.5	47.5
All Sites Male	21	32.7	65.8	117	196	307
All Sites, Female	24.4	46.3	86.1	150	232	322
Average Cancer Rate	22.7	39.5	76.0	134	214	314
Using Fit to Power function	21.0	43.3	79.0	132	208	311

From the fit, the cancer incidence at 33.3 and 36.3 was calculated:

Cancer Incidence at age:
	Age	Cancer Incidence
	33.3	86.3
	36.3	117.7

 Expected factor increase in 3 years in cancer incidence = 117.7/86.3 = 1.36    

All Cancers expected was                                                      114.9 in Hwang 2006 paper (See Table III above)

All Cancers expected 3 years later would be 114.9*1.36 =          156

Page 145 of follow-up paper (Hwang et al., 2008) says:

All Cancers observed 3 years later was             128  (in Hwang 2008 paper)

Observed/Expected     (128/158):                       0.82

 Thus, there is a 18% reduction in cancers observed in the follow-up paper                                                        

The reduced overall cancer incidence continues, but this information is not mentioned in the paper, as they did not repeat the SIR calculation for cancers.  On the other hand, they used proportional hazard (LNT) model to estimate excess cancer risk, as described on page  144 of the Hwang 2008 paper.

                                               

The paper's conclusions are misleading in depicting the carcinogenic effects of low dose radiation.     

References:

Hwang SL, Guo HR, Hsieh WA, Hwang JS, Lee SD, Tang JL,Chen CC, Chang TC, Wang JD and Chang WP. 2006. Cancer risks in a populationwith prolonged low dose-rate gamma-radiation exposure in radiocontaminatedbuildings, 1983-2002. Int J Radiat Biol 82: 849-58.

Hwang SL, Hwang JS, Yang YT, Hsieh WA, Chang TC, GuoHR, Tsai MH, Tang JL, Lin IF and Chang WP. 2008. Estimates of relative risksfor cancers in a population after prolonged low-dose-rate radiation exposure: afollow-up assessment from 1983 to 2005. Radiat Res  170: 143-8.