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Dr. Tsubokura's Radiation Lecture Vol.27

Author: Masaharu Tsubokura

Editors: Akihiko Ozaki M.D., Yuki Senoo

53. Shipping restriction limits internal radiation exposure

The health effects of radiation exposure, namely increased risk of cancer, are related to the level of exposure. As such, the risk of thyroid cancer depends on the extent of a person’s exposure to radioactive iodine.

Reportedly, the biggest contamination pathway induced by radioactive iodine after the Chernobyl accident was as follows: cows in the affected area ate grass contaminated by radioactive iodine, which became condensed in the milk the cows produced. People continued to drink this milk not knowing that it was contaminated.

In contrast, in the case of Fukushima, the reference value for “radioactive iodine” was implemented just six days after the accident (March 17, 2011), and food inspections and shipping restrictions began. This reference value was designed with an emphasis on safety: a person who consumes food which contains radioactive iodine within the reference value on a daily basis for one year will not exceed the upper limit of annual radiation exposure.

This is one reason the level of thyroid exposure to radioactive iodine in Fukushima was significantly lower than after the Chernobyl accident.

54. Lumps on the thyroid could be benign

In Fukushima Prefecture, ultrasound screenings are conducted to check for the presence of encapsulated liquid sacs (cysts) and lumps (nodules) on thyroid glands.

A cyst is a reservoir of thyroid hormonal material that may appear and vanish over time. It is therefore not precancerous.

Does this mean a nodule is precancerous?

Well, that is also not true.

In some cases, nodules may be diagnosed as cancer, but in many cases, such lumps are benign. They do not change in size over time and may even become smaller.

Furthermore, some people are born with a thymus that inverts into the thyroid gland, which appears to be a nodule-like structure during an ultrasound examination.

Whatever the case, just because there is a nodule (a lump), you should not jump to the conclusion that it is cancer. The decision to conduct further examinations is made based on the size and appearance of nodules found during an ultrasound examination.


The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, on January 10th 2016 and January 17th 2016 was reproduced for MRIC Global under the author's permission.

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