Study into radiation exposure finds alarming results

A long-term study of survivors of the atomic bombings of Hiroshima and Nagasaki has found that even modest exposure to radiation increases the long-term risk of developing tumours of the nervous system.

Researchers at the Radiation Effects Research Foundation in Hiroshima, Japan, have assessed survivors of the atomic bombings since the Second World War, issuing regular reports on the effects of radiation exposure in this population. Dale Preston and colleagues from the foundation has published this report in the October 16 issue of the Journal of the National Cancer Institute.

Radiation up to 10,000 times that produced by a chest x-ray was exposed to these people which is more than 50 times the yearly exposure considered safe for people who work with radioactive materials.

The medical records of 80,160 atomic bomb survivors were analysed in this current study. Investigators found a significant relationships between the amount of radiation exposure during the bombings and a person’s risk for developing tumors of the nervous system.

A total of 467 primary nervous system tumors and pituitary gland tumors were found among the group.

“The study provides new information on the effects of radiation on specific types of brain tumors and suggests that increased nervous system tumor risks are seen at moderate radiation doses… in the range of 0.5 to 50 roentgen equivalent man (rem),” Preston said.

Schwannomas, a benign tumour of the cells insulating nerve fibres, were seen as being the highest risk of developing, which according to Preston, “have very good prognosis”. For other tumours (than Schwannomas) there is a suggestion that risks may be higher for men than women and for those exposed as children.

“As with other radiation-associated solid cancers the increase appears to persist throughout life following exposure,” added Preston.

Preston also noted that although there are clearly increased risks of nervous system tumours associated radiation exposure, the risks are proportional to dose, so risks associated most risks associated with most radiation exposures are not large.

About 15% of the 228 nervous system tumors among the atomic bomb survivors in the study who were exposed to an average dose of about 12.5 rem could be attributed to their radiation exposure, according to Preston.

“In total, more than 12,000 cancers developed among cohort members during the study follow-up period and about 6% of these were associated with radiation exposure from the bombings,” the researcher said. “Because nervous system tumors are rare, the chance of developing a radiation-related tumor of the nervous system is small”.

“Since radiation can cause cancer, even at low doses, unnecessary exposure should be avoided,” Preston concluded. “However, the well-established benefits from appropriate diagnostic and therapeutic radiation outweigh the risks.”

(Source: Reuters Health & ASCO)