A copy of the former Ministry of Health and Welfare notice stating that the ministry did not object to using irradiation by X-rays for eugenic sterilization as long as it was for academic research purposes is seen. (Mainichi, image partially modified)

While using X-ray radiation for sterilizations was prohibited under the now-defunct eugenics protection law (1948-1996), the former Ministry of Health and Welfare decided in 1949 that it had "no objections" to the practice if it was for research purposes, it has been learned.

The decision notice was kept at the Kyoto Institute, Library and Archives, and copies of documents including the notice bearing the name of the then head of the health ministry's sanitation department were obtained by the Mainichi Shimbun.

It is current medical knowledge that if testes or ovaries are exposed to a certain amount of X-rays, they are rendered impotent. However, the radiation also poses the danger of damaging nearby organs as well. There is suspicion that those individuals with disabilities, mental illnesses or hereditary disorders that underwent forced sterilization surgeries under the eugenics law may have been used as subjects for dangerous research, and experts are calling for a need to clarify what actually occurred.

The notice was a reply to the Kyoto Prefectural Government, after the latter received an inquiry from the Faculty of Medicine at Kyoto University about the pros and cons of X-ray irradiation for research purposes. Because the eugenics protection law did not allow for the use of X-ray irradiation for sterilization, the prefectural government added that there was "a question as to whether it can be allowed in the special case of academic research."

The head of the ministry's sanitation department then sent a notice to the Kyoto governor that while sterilization by irradiation was "outlawed by Article 28 of the eugenics protection law," it would be allowed as the ministry was "not opposed to it being carried out for the purpose of academic research at university (medical departments) and other institutions."

In the same archives, there are also documents that show that the Kyoto Prefectural Government then relayed the ministry's verdict to Kyoto University and Kyoto Prefectural University of Medicine, but there were no records confirming that the institutions actually carried out the research.

According to professor Koji Tsuboi, a physician at the University of Tsukuba Hospital Photon Beam Therapy Center in Ibaraki Prefecture, it is known that undifferentiated egg and sperm cells lose the ability to undergo cell division when exposed to X-ray radiation, and this leads to a person becoming sterile, but such a procedure is currently not utilized for the purpose of sterilization.

This is because it comes with an extremely high risk to the patient, such as the development of cancer or inflammation of the intestine due to the relatively high dose of radiation -- in order to sterilize a human, at least 250 to 600 times the radiation of a regular X-ray for ovaries and 350 to 600 times for testes is needed, according to the International Commission on Radiological Protection.

The Ministry of Health, Labor and Welfare's Maternal and Child Health Division issued a statement saying, "As we cannot confirm relevant documents, we will refrain from commenting," while a public relations representative from Kyoto Prefectural University of Medicine also declined to comment on the matter.