Dr. Tsubokura's Radiation Lecture Vol.52
Author: Masaharu Tsubokura
Editors: Akihiko Ozaki M.D., Yuki Senoo
103. Medical radiation does not increase lung cancer risk
The impact of radiation on health is determined by the extent of the exposure dose, not by whether one has experienced any exposure in the past. In that case, what level of radiation exposure is deemed dangerous? Numerous investigations have been conducted to find answers to this question, including those for medical radiation,1 natural background radiation,2 and occupational radiation exposure.3
Well-known previous research papers on the topic of medical radiation are ones that investigated the risks of breast and lung cancer due to radiation exposure during chest examinations for pulmonary tuberculosis. In the first half of the 20th century, it was common practice to artificially induce a pneumothorax (collapse a part of the lungs) as a surgical treatment for pulmonary tuberculosis. During this operation, it was necessary to apply radiation to the patient’s chest to guide the procedure by constantly monitoring (seeing through) the lung.
Because it was necessary to repeat this procedure several times a month for several years, the patients received a high level of radiation exposure, which was equivalent to more than 100 times the dose received during a chest CT and more than 1000 times the dose received during a chest X-ray. Although this procedure was necessary for medical purposes, the radiation level was still considerable.
Although the patients received a considerably high level of radiation exposure, no significant increase in lung cancer among these patients was found. On the other hand, it was reported that breast cancer among younger patients increased. Furthermore, the relationship between risk of solid cancer deaths and the level of radiation exposure calculated from these tuberculosis studies was found to be almost identical to that reported in research on radiation-related health effects after the atomic bombing of Hiroshima and Nagasaki.
104. Natural background radiation does not increase cancer risk
The impact of radiation on health is determined by the extent of the exposure, not by whether one has experienced any exposure in the past. In that case, what level of radiation exposure is deemed dangerous? Numerous investigations have been conducted to find answers to this question, including studies on medical radiation,1 natural background radiation,2 and occupational radiation exposure.3
In previous research on natural background radiation, several studies were conducted in areas with high natural background radiation: one of the most well-known areas on the southeastern coast of Brazil (Ganapati), Kerala in India, and Ramsar in Iran. In these regions, high levels of radioactive substances such as thorium and radium are present in the environment. Moreover, the levels of natural background radiation are approximately 2 to 10 times higher than the average level in Japan.
For example, in Kerala (India), the average and maximum levels of annual external radiation exposure are 4 millisieverts and several tens of millisieverts, respectively. Since the 1990s, various research on radiation-related health effects has been conducted in this region, and no significant increase in cancer incidence or mortality has been reported up to the present.
In addition, it was reported that in high natural background radiation areas, there was no significant difference in the sex ratio of newborn babies, congenital disabilities, miscarriages, stillbirths, or infant mortality compared to other countries.In addition, although Guarapari used to be one of the most well-known high natural background radiation areas, the current level of radiation has decreased due to asphalt paving, which is working as a shield.
----------------------------------------------------------------------------------------------------------
The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, on December 25th 2016 and on January 8 2017 was reproduced for MRIC Global under the author's permission.