© 2017 MRIC Global

Dr. Tsubokura's Radiation Lecture Vol.40

May 28, 2019

Author: Masaharu Tsubokura

Editors: Akihiko Ozaki M.D., Yuki Senoo

 

79. The other cells effectively replace the damaged or lost function of the body

The previous articles explained deterministic effects: a significantly high level of radiation exposure definitely causes sets of symptoms such as hair loss, bleeding, diarrhea, and burns (erythema), while a sufficiently low level of exposure will never result in such adverse health effects.

 

This “deterministic effect” is caused by radiation exposure-induced cell death. Furthermore, our bodies are made up of approximately 60 trillion cells, and a certain low percentage of human cells are renewed and effectively replaced every day. Even if we assume that 1% of the entire cells in our bodies are replaced every year, this could be equal to at least 600 billion cell deaths.

 

However, this does not make us feel as if there is something wrong with our bodies. This is because many other remaining cells adequately compensate for the function of lost cells. The “deterministic effect” occurs when the compensation function of surviving cells is not able to support the lost functions of a large number of dead cells due to the damage from radiation exposure.

 

The reason why the “deterministic effect” will never appear in current radiation exposure received in daily life is that the level of radiation exposure is far below the level that would kill a large number of cells.

 

 

80. “Threshold limit value” for deterministic effect

The previous articles explained “deterministic effects”: a significantly high level of radiation exposure every time causes sets of symptoms such as hair loss, bleeding, diarrhea, and burns (erythema), while a sufficiently low level of exposure will never result in such adverse health effects.

 

The impact of radiation on health is determined by the extent of the exposure dose. The level of radiation exposure that would determine whether an affected person would develop or would not develop specific symptoms (such as bleeding) is called the “threshold limit value.” You will not develop any deterministic effects for a lifetime unless you receive a high level of radiation that exceeds this “threshold limit value” all at once.

 

The “threshold limit value” for radiation exposure varies from several hundred to thousands of millisieverts, depending on the types of symptoms. This approximately accounts for the radiation exposure that we would receive in our daily life from the natural environment for 100 years.

 

In contrast, it is believed that we should not speculate that the “threshold limit value” is present for cancer. This means that as the radiation exposure increases, there is an increasing probability of developing cancer in the future. In contrast to the “deterministic effect,” this type of radiation effect is called the “stochastic effect.”

 

 

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

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