Sharp rise in CT scans on children and adults
There has been a sharp rise in the number of people having CT scans in the UK, according to experts assessing the risks of radiation on health.
The number of scans on children - who are most at risk - doubled over the past decade to 100,000 a year in 2012.
Concerns centre around evidence radiation can increase the chance of developing cancer.
But the government-appointed Comare group said the benefits of scans usually outweigh the harms.
During a CT (computerised tomography) scan, an X-ray tube rotates around the patient's body to produce detailed images of internal organs and other parts of the body.
The Committee on Medical Aspects of Radiation in the Environment (Comare) estimated that the number of scans carried out each year reached a record of five million in 2013-2014.
Figures were based on data gathered from a third of UK hospitals - but experts warned without more information they could not accurately assess how many cases of cancer this radiation may be linked to.
They urged the government to make it mandatory for hospitals to report the number of scans and the doses of radiation they use.
Prof Alex Elliott, who led the committee, said: "At the moment these (surveys) happen almost on an ad-hoc basis and that means we don't have decent data on which to carry out the epidemiological studies.
"We need to know what the dose to the people was otherwise, we can't work out what the risk might be."
Though the group felt the majority of CTs were justified they warned clinicians need to be aware of certain groups who are more susceptible to the harms of radiation.
Children are at more risk as they have a longer lifespan during which they can accumulate more exposure to radiation.
A 2012 study suggested multiple CT scans (over 10) in childhood could triple the risks of developing brain cancer or leukaemia.
And women who carry the BRAC1 and BRAC1 gene mutations are also more sensitive to radiation, according to the report.
The team emphasised doctors need to minimise risks, by ensuring they use scans that answer clinical questions - not necessarily ones producing the most detailed images.
They estimate 16% of the radiation people are exposed to in the UK comes from non-natural sources. And some 90% of this comes from medical interventions.
They said the UK holds one of the best records in the world.
The Royal College of Radiologists said: "Radiologists are more aware than most of the remarkable growth in the use of CT over the past decade.
"This has undoubtedly brought benefit to patients but carries attendant risks from the radiation dose involved.
"Clinical radiologists have always accepted their responsibilities in the area of radiation safety."