7 June 2012 Last updated at 03:05 GMT
CT scans on children 'could triple brain cancer risk'
By Jane Dreaper
Health correspondent, BBC News
The study looked at the records of nearly 180,000 young patients
Multiple CT scans in childhood can triple the risk of developing brain cancer or leukaemia, a study suggests.
The Newcastle University-led team examined the NHS medical records of almost 180,000 young patients.
But writing in The Lancet the authors emphasised that the benefits of the scans usually outweighed the risks.
They said the study underlined the fact the scans should only be used when necessary and that ways of cutting their radiation should be pursued.
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.
In the first long-term study of its kind, the researchers looked at the records of patients aged under 21 who had CT scans at a range of British hospitals between 1985 and 2002.
Because radiation-related cancer takes time to develop, they examined data on cancer cases and mortality up until 2009.
Brain cancer and leukaemia are rare diseases.
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The important thing is that parents can be reassured that if a doctor in the UK suggests a child should have a CT scan, the radiation and cancer risks will have been taken into account”
Professor Sir Alan Craft
The study estimated that the increased risk translated into one extra case of leukaemia and one extra brain tumour among 10,000 CT head scans of children aged under ten.
Dr Mark Pearce, an epidemiologist from Newcastle University who led the study, said: "We found significant increases in the risk of leukaemia and brain tumours, following CT in childhood and young adulthood.
"The immediate benefits of CT outweigh the risks in many settings.
"Doses have come down dramatically over time - but we need to do more to reduce them. This should be a priority for the clinical community and manufacturers."
CT scans are useful for children because anaesthesia and sedation are not required.
This type of check is often ordered after serious accidents, to look for internal injuries, and for finding out more about possible lung disease.
Regulations on their use in the UK mean CT scans should only be done when clinically justified - and the researchers said their study underlined that point.
Professor Sir Alan Craft, a co-author and leading expert in child health, said: "The important thing is that parents can be reassured that if a doctor in the UK suggests a child should have a CT scan, the radiation and cancer risks will have been taken into account.
"There's a much greater risk of not doing a CT scan when it's suggested.
"This study will push us to be even more circumspect about using it. We have much stricter rules here about using CT than in the United States, for example."
Dr Hilary Cass, the president of the Royal College of Paediatrics and Child Health, said: "We have to take very seriously the link between repeated CT scans and increased risk of these cancers amongst children and young people.
"But with both tumours rare, the absolute risk remains low."
A Department of Health spokesman said: "The UK uses lower levels of radiation in CT scans than other countries.
"We also have clear regulations to ensure a CT scan is only carried out when clinically justified."
The Lancet, Early Online Publication, 7 June 2012
doi:10.1016/S0140-6736(12)60815-0Cite or Link Using DOI
Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study
Dr Mark S Pearce PhD a , Jane A Salotti PhD a, Mark P Little PhD c, Kieran McHugh FRCR d, Choonsik Lee PhD c, Kwang Pyo Kim PhD e, Nicola L Howe MSc a, Cecile M Ronckers PhD c f, Preetha Rajaraman PhD c, Alan W Craft MD b, Louise Parker PhD g, Amy Berrington de Gonzalez DPhil c
Although CT scans are very useful clinically, potential cancer risks exist from associated ionising radiation, in particular for children who are more radiosensitive than adults. We aimed to assess the excess risk of leukaemia and brain tumours after CT scans in a cohort of children and young adults.
In our retrospective cohort study, we included patients without previous cancer diagnoses who were first examined with CT in National Health Service (NHS) centres in England, Wales, or Scotland (Great Britain) between 1985 and 2002, when they were younger than 22 years of age. We obtained data for cancer incidence, mortality, and loss to follow-up from the NHS Central Registry from Jan 1, 1985, to Dec 31, 2008. We estimated absorbed brain and red bone marrow doses per CT scan in mGy and assessed excess incidence of leukaemia and brain tumours cancer with Poisson relative risk models. To avoid inclusion of CT scans related to cancer diagnosis, follow-up for leukaemia began 2 years after the first CT and for brain tumours 5 years after the first CT.
During follow-up, 74 of 178 604 patients were diagnosed with leukaemia and 135 of 176 587 patients were diagnosed with brain tumours. We noted a positive association between radiation dose from CT scans and leukaemia (excess relative risk [ERR] per mGy 0・036, 95% CI 0・005?0・120; p=0・0097) and brain tumours (0・023, 0・010?0・049; p<0・0001). Compared with patients who received a dose of less than 5 mGy, the relative risk of leukaemia for patients who received a cumulative dose of at least 30 mGy (mean dose 51・13 mGy) was 3・18 (95% CI 1・46?6・94) and the relative risk of brain cancer for patients who received a cumulative dose of 50?74 mGy (mean dose 60・42 mGy) was 2・82 (1・33?6・03).
Use of CT scans in children to deliver cumulative doses of about 50 mGy might almost triple the risk of leukaemia and doses of about 60 mGy might triple the risk of brain cancer. Because these cancers are relatively rare, the cumulative absolute risks are small: in the 10 years after the first scan for patients younger than 10 years, one excess case of leukaemia and one excess case of brain tumour per 10 000 head CT scans is estimated to occur. Nevertheless, although clinical benefits should outweigh the small absolute risks, radiation doses from CT scans ought to be kept as low as possible and alternative procedures, which do not involve ionising radiation, should be considered if appropriate.
US National Cancer Institute and UK Department of Health.
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