US researchers say that the cancer risks of Computed Tomography (CT) scans may be greater than previously estimated.

The Press Association reports that lead researcher Professor Rebecca Smith-Bindman – from the University of California at San Francisco – found that doses of radiation given during CT scans were generally higher than thought.

CT scans are used to take cross-sectional X-rays that offer a detailed 3D image of internal organs, blood vessels and bones. They are most commonly used to detect tumours developing in the body.

All X-ray technology carries a slight risk of radiation, but CT scans are known to offer a greater risk than X-rays such as mammograms – and doses of radiation from CT scans were ‘generally higher than reported’. The researchers found that there was a 13-fold ‘variation’ between the lowest doses of radiation, compared with the highest doses.

Prof Smith-Bindman said:

‘If a physician sent a patient for a particular CT procedure, the dose that patient would have received varied by this much.

‘The risk associated with obtaining a CT is routinely quoted as around one in 1,000 patients who undergo CT will get cancer. In our study, the risk of getting cancer in certain groups of patients for certain kinds of scans was as high as one in 80.’

Prof Smith-Bindman added that one CT scan was – in terms of radiation dosage – the equivalent of undergoing ‘74 mammograms or 442 chest X-rays’.

In a separate study published in the same journal, another team of researchers found that in the US, around 29,000 cases of cancer could be linked to CT scans performed in 2007 – including approximately 14,000 cancers resulting from abdominal and pelvic scans, a total of 4,100 developing after chest scans, 4,000 from head scans and 2,700 from heart and blood vessel scans.

The second study found that two-thirds of the predicted cancers would occur in women, thought to be more sensitive to radiation than men.

Both studies are published in the ‘Archives of Internal Medicine’.

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