Low levels of medical radiation can cause cancer, HKU study warns

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A chest X-ray is equivalent to 10 days' absorption of Americans' annual average intake of naturally occurring ionising radiation. Photo: Xinhua

Worries have been raised about the overuse of radiation in medicine after a study shows that even low levels of radiation - such as those emitted by X-rays and CT scans - can cause cancer.
The risk of soft-tissue sarcoma is doubled if a person receives an amount of radiation equivalent to two CT head scans, University of Hong Kong researchers say.

This means that people who join a growing trend of getting frequent whole-body checks including X-rays and scans are putting themselves at risk, the researchers say, adding that authorities should also reconsider the risks of nuclear power.
"The study has highlighted that even low to moderate levels of exposure are enough to cause genetic mutation," study leader Dino Samartzis said.
While it was difficult to project the risk of cancer precisely, "the conclusion is simple - we should avoid all unnecessary exposure to radiation as much as we can", said Samartzis, a research assistant professor in HKU's department of orthopaedics and traumatology.
The researchers used data from a lifespan study of more than 80,000 Hiroshima and Nagasaki atomic-bomb survivors.
Recent studies show the amount of radiation released for medical use in America surged fourfold from the 1980s to 2006, and is higher than the amount released by the two nuclear bombs in 1945.
There is also increased use of radiation in Hong Kong as annual body checks became popular among adults and even children, Samartzis said. Individuals and medical practitioners have to rethink the risk from ionising radiation, which is used in procedures such as radiographs, CT scans and fluoroscopy, he said.
The American College of Radiology says Americans on average each year absorb about 3 millisieverts (mSv) - a measure of the concentration of ionising radiation absorbed per unit of a material's mass - from naturally occurring radioactive matter and outer space.
A chest X-ray is equivalent to 10 days' absorption of this amount and a CT scan is equivalent to three to seven years' absorption.
The report notes that in assessing the harm of radiation in the human body, atomic-bomb survivors in Japan are the world's largest source of information.
The victims were exposed to whole-body ionising radiation at the time of the bombings in 1945.
It is known that the group develops cancers and other diseases at a higher rate than the general population, but this study confirms a more delicate condition in sarcomas.
Among the 80,180 people being assessed for cancer, the disease was identified in 104 of them. It suggests that the risk of having soft-tissue sarcoma will be doubled under an exposure equal to radiation from two CT head scans.
"If a low level of exposure is enough to affect bone and soft tissue, it will most definitely affect other parts of the body," Samartzis said.
"With increased public awareness, hopefully we can also see a change in government policy in areas such as handling nuclear power."