Small cancer risk following CT scans in childhood confirmed

New research has found a small increase in cancer risk following exposure to CT scans in children and young people.
The study used anonymised medical records for 11 million young Australians, including 680,000 who were exposed to CT scans between 1985 and 2005.
The Australian researchers, with colleagues at Oxford University and the International Agency for Research on Cancer in France, found that for every 1,400 CT scans before the age of 20 there was one extra case of cancer over the following 10 years.
This small increase in cancer risk must be weighed against the undoubted benefits from CT scans in diagnosing and monitoring many different health conditions.
In most cases, the benefits of having a scan clearly outweigh the risk. But these new findings will remind doctors to order CT scans only when there is a definite medical reason and to insist that CT scans use the lowest possible X-ray dose, say the researchers.
The research team was led by Professor John Mathews at the University of Melbourne.
Professor Mathews says: ‘CT scans have great medical benefits. In the same way that standard X-rays are helpful in bone fractures, CT scans can provide detailed three-dimensional pictures to diagnose or exclude disease in any suspect part of the body.
‘As an individual patient, your risk of cancer from a CT scan is very low. In the vast majority of cases the benefits of a CT scan in diagnosing a condition or guiding treatment will outweigh the risks. I’d certainly have a CT scan if a doctor said ‘I think you should have a scan’ and explained why I needed it.
‘Nevertheless, it is clear from our study that it is important for doctors to use CT scans only where they are necessary. By reducing the number of scans performed in a large population, there will be a small but corresponding reduction in the number of cancers in later years.’
CT scans use multiple X-ray images to produce detailed images of structures inside the body including the internal organs, blood vessels, bones and tumours.
It is already well known that large doses of radiation can damage DNA and increase the risk of a later cancer. However, the radiation doses from CT scans are very small, and there has been uncertainty about whether such small doses would really cause cancer, and whether any small increase in risk could be measured reliably.
This new Australian study was able to answer this question by linking anonymised Medicare records of CT exposures for the entire population of young Australians, aged 0-19 years between 1985 and 2005, to cancers diagnosed up to the end of 2007. It is not yet known what will be seen with longer follow-up. Oxford University