PARIS: Children exposed to multiple CT scans could
be up to three times likelier to contract cancer of the blood, brain or bone
marrow later in life, according to research published on Thursday.
Writing
in The Lancet medical journal, a team of scientists in Canada, Britain and the
United States said the cancer risk, in absolute terms, appears to be small.
But
they appealed for radiation doses from CT scans to be kept at a minimum and for
alternatives to be used where appropriate.
The
researchers claimed their study was the first to provide direct evidence of a
link between exposure from CT radiation in childhood and later cancer risk.
"Of
utmost importance is that where CT is used, it is only used where fully
justified from a clinical perspective," said lead author Mark Pearce of
Newcastle University's Institute of Health and Society.
As a
vital diagnostic technique, use of the CT scan has increased rapidly in the
past 10 years, particularly in the United States, the researchers said.
"However,
potential cancer risks exist due to the ionising radiation used in CT scans,
especially in children who are more radiosensitive than adults."
Computerised
tomography - commonly known as CT - is an X-ray technique that produces images
of the body's internal structures in cross sections.
The
researchers studied nearly 180,000 people who underwent a CT scan as children
or young adults (under 22) in Britain between 1985 and 2002.
Of
these, 74 were subsequently diagnosed with leukaemia and 135 with brain cancer
according to data for the period 1985 to 2008.
The
team calculated that compared to patients who received a radiation dose of less
than five milli-Grays (mGy), those who were given a cumulative dose of 30 mGy
had about three times the risk of developing leukaemia (cancer of the blood or
marrow) later in life.
Those
who received 50 to 74 mGy had thrice the risk of brain tumours.
The
study did not compare children who had been scanned against those who had not
been scanned.
Put
into context, this means that among every 10,000 patients who received one CT
scan before the age of 10, there would be one extra case of leukaemia and one
extra brain tumour per 10 mGy of radiation in the 10 years after exposure.
"Further
refinements to allow reduction in CT doses should be a priority, not only for
the radiology community, but also for manufacturers," said Pearce.
"Alternative
diagnostic procedures that do not involve ionising radiation exposure, such as
ultrasound and MRI (magnetic resonance imaging) might be appropriate in some
clinical settings."
Commenting
on the study, Andrew Einstein of the Columbia University Medical Centre in New
York said Pearce and his colleagues' work confirmed that CT scans "almost
certainly produce a small cancer risk".
"Use
of CT scans continues to rise, generally with good clinical reasons, so we must
redouble our efforts to justify and optimise every CT scan."
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AFP/de
