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Rediff.com  » News » CT scan could cause cancer, but hey, don't worry

CT scan could cause cancer, but hey, don't worry

November 29, 2007 14:52 IST

A study in the New England Journal of Medicine, now getting considerable play across the international press, says two diametrically opposite things: One, that radiation from the computed tomography scanning (CT scan) machines that are widely used as a diagnostic aid can cause cancer; and, two, that this risk shouldn't stop you from using such machines anyway.

The study, done by researchers at the Columbia University Medical Center in New York, suggests that CT scans already done will cause a good two per cent of all cancers in the US over the next 20 to 30 years.

The researchers, and other experts, add that while they are comfortable tracing a link between CT scans and cancer, they don't have sufficient empirical evidence to go out on a limb and quantify the magnitude of that risk.

'It has been pretty clearly demonstrated that [radiation] doses in CT scans have increased cancer risk,' study author David Brenner, a professor of radiation oncology at Columbia, is quoted as saying. 'Although the risks for any one person are not large, the increasing exposure to radiation in the population may be a public health issue in the future.'

More alarmingly, researchers say children are 10 times as sensitive to the radiation as adults are -- hence the postulate that they are more likely to develop cancers from CT scan-induced radiation, since their longer lifespan means the cancer has a larger time frame to incubate in.

The study based its estimates on a single study showing an excess risk of cancer death among survivors from the Hiroshima and Nagasaki bombings of World War II. The study points out that people miles removed from Ground Zero received radiation doses similar to those you will get from CT scans.

Analysts have trashed the finding, pointing out that you cannot extrapolate atom bomb data to medical radiation since the former is gamma radiation absorbed in one single exposure, whereas the latter is beta radiation that is low-energy and less easily absorbed.

One point of agreement, however, as ABC News notes in its report of the study, is that researchers and radiologists alike agree too many CT Scans are being performed -- in the US alone, that number has increased from 3 million in 1980 to more than 68 million today.

ABC quotes Dr Devra Davis, director of the Center for Environmental Oncology at the University of Pittsburgh Cancer Institute,  as giving two reasons for this increase. 'First, we are tempted to use technology simply because it is available even when it's not necessary,' she says. 'We tend to use this kind of technology without thinking about negative health impacts down the road.

'Second are issues of defensive medicine. The growth in lawsuits has put doctors on high alert to use all technologies at their availability to diagnosis patients.'

The authors of the study point to this same set of figures to underpin their argument: 'If it is true that about one-third of all CT scans are not justified ... perhaps 20 million adults and, crucially, more than 1 million children per year in the United States are being irradiated unnecessarily,' ABC quotes them as saying.

The bottom line is, since there is a real, if unquantified, risk that such scans can trigger cancer, experts say the solution is to cut back on such tests and use other imaging techniques such as MRIs and ultrasound instead.

The Rediff News Bureau