9 Octobre 2015
October 8, 2015
A study examining thyroid cancer among children 18 years and younger when the Fukushima nuclear catastrophe began, found an increase in thyroid cancers, as predicted by World Health Organization (WHO) initial dose assessments.
However, lead researcher, Toshihide Tsuda an epidemiologist at Okayama University, says “[t]his is more than expected and emerging faster than expected…” by either WHO predictions (slide 4) or studies of thyroid cancers after the Chernobyl nuclear explosion in 1986 (slide 31). Tsuda was urged by international experts, and the publishing journal, to publish his study as early as possible, due to its potential implications for public health.
There were no precise measurements of internal or external radiation exposure, so researchers used residential addresses at the time the catastrophe began in 2011 as a surrogate for dose.
A second round of screening, to be completed in March 2016, will include those who were in utero in 2011. Data already show an additional 25 thyroid cancers.
The highest incidence rate ratio was among people whose district was not evacuated, 50 to 60 km (30 to 40 miles approximately) west from the Fukushima nuclear reactors. Data show 605 thyroid cancer cases per million examinees. The expected cases of thyroid cancer for children is 1-2 per year per million.
Ground contamination does not necessarily reflect exposure. Some of the most exposed people came from areas where radionuclide deposition was minimal, but radioactive iodine in the air as a result of the catastrophe still exposed them.
The magnitude of the increase is too great to be explained by increased screening since available data show a 2 to 3- and at most a 6 to 7–fold increase would be attributable to enhanced screening efforts. The data examined by Tsuda show cancer cases an order of magnitude higher.
The cancers found by this screening in Fukushima prefecture had metastasized to lymph nodes in 74% of cases (40 cases out of 54), meaning these cancers were not in early stages of development. Therefore, when interpreting the data, overtreatment is also not an issue; a conclusion shared by doctors who helped treat these patients.
Contrary to claims that we would not be seeing an increase in cancers this early (within a year after exposure to radioactivity), radioactivity from Fukushima could have caused this increase in thyroid cancers because excess cancers were observed subsequent to Chernobyl in the earlier years. Further, the US CDC recognizes (slide 8) a minimum empirical induction time for thyroid cancer of 2.5 years in adults; and 1 year in kids for all cancers including thyroid. The minimum latency for leukemia is 0.4 years (146 days).
Residents who were older than 18 years in 2011 should also be monitored for thyroid cancers.
In addition to predicting increases in thyroid cancers, the WHO also predicted increases in leukemias and breast cancer among others. The WHO acceded to demands by the government of Japan to reduce estimated doses (slide 5 and also this link). As a result, doses listed in the WHO’s report are 1/3 to 1/10th lower than initially drafted.
The study concludes: “In Chernobyl, excesses of thyroid cancer became more remarkable 4 or 5 years after the accident in Belarus and Ukraine, so the observed excess alerts us to prepare for more potential cases within a few years. Furthermore, we could infer a possibility that exposure doses for residents were higher than the official report or the dose estimation by the World Health Organization, because the number of thyroid cancer cases grew faster than predicted in the World Health Organization’s health assessment report.”