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CT scan raises cancer risk

June 7, 2012

Children subjected to CT scans with high radiation doses face a three-times increased risk of suffering from leukaemia and brain cancer during their lifetime.
In the most conclusive evidence till date, a study published in the Lancet on Wednesday says radiation exposure received from two to three CT scans of the head in childhood (aged under 15) — giving a cumulative dose of around 60 milli-Grays (mGy) can triple the risk of later developing brain cancer. On the other hand, around 5 to 10 such scans (cumulative dose of around 50 mGy) could triple the risk of developing leukaemia.
The authors from Newcastle University studied 180,000 patients who underwent a CT scan between 1985 and 2002 from 70% of UK hospitals.
They extracted the number and types of CT scan from the records and estimated the dose absorbed in mGy by the brain and bone marrow in patients for each scan. These data were then linked to cancer incidence and mortality reports in the UK National Health Service Registry between 1985 and 2008.
From this, they calculated excess incidence of leukaemia and brain tumours. The dose of radiation received by the brain and bone marrow varied by age and body part scanned.
Atotal of 74 from 178,604 patients were diagnosed with leukaemia and 135 of 176,587 were diagnosed with brain cancer.
The authors say that, of every 10,000 people between the ages of 0-20 receiving 10 mGy from a CT scan, there would be about one expected excess leukaemia case, whereas there were would be one excess case of brain cancer for every 30,000 people.
Applying the dose estimates for one head CT scan before the age of 10, this would translate into approximately one excess case of leukaemia and one excess brain tumour per 10,000 patients in the decade after the first exposure.
Lead author Dr Mark Pearce Pearce says, in the UK, the Ionising Radiation (Medical Exposure) Regulations mean that a CT scan should only be done when clinically justified.Reacting to the study, eminent radiologist Dr Harsh Mahajan said: “I agree with the findings of the study. Unnecessary CT scans and radiation exposure has been found to cause cancer. However, such high radiation doses were more common in CT machines used a decade ago. The present multi-slice CT scans expose patients to extremely low radiation levels.”

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Categories: Radiology
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