People who pay for whole-body CT scans, in the hope of finding tumours at their earliest stages, may ironically be raising their overall risk of cancer, according to a new study. The radiation from a single whole-body scan is equal to that from 100 mammograms and is similar to that received by survivors of the atomic bombings of Hiroshima and Nagasaki - about 2.4km from the explosions - according to radiation biologist David Brenner of Columbia University. The radiation from one scan is enough to produce one tumour in every 1,200 people who undergo the procedure, say Mr Brenner and co-author Carl Elliston in the journal Radiology. For those who have annual scans, the risk goes up to as high as one tumour in every 50 people. 'The risks for a single scan are not huge,' Mr Brenner says. 'But if you have them repeatedly, the risk starts to build up quite a lot and becomes significant.' He cautions that his results apply only to healthy individuals who choose to receive the scans. 'The risk-benefit equation changes dramatically for adults who are referred for CT exams for medical diagnosis,' he says. 'Diagnostic benefits far outweigh the risks', informs the Straits Times. According to New Scientist,Patients undergoing a full-body computed tomography (CT) scan are exposed to a radiation dose equivalent to that received by some survivors of the Hiroshima and Nagasaki atomic bombs, say US researchers. This exposure has been linked with a significant rise in cancer mortality and younger patients are especially at risk. CT scanners rotate around the body taking a series of cross-sectional X-ray “slices”, which are compiled by computer to produce a 3D portrait of internal organs and structure. The radiation dose received is often 500 times that of a conventional and nearly 100 times that of a mammogram. While those patients referred for diagnostic CT scans by medical practitioners should see benefits that far outweigh the risks, those who self-refer may be increasing their risk of cancer unduly. X-rays from a single full-body CT scan give a dose of radiation similar to cancer-associated radiation doses in A-bomb survivors, finds David J. Brenner, PhD, director of Columbia University's center for radiological research. It's not a huge risk, especially for someone with symptoms of a dangerous condition. But when used to screen healthy people for hidden evidence of disease, the risk may outweigh the benefit. And if a healthy person gets repeated full-body scans, cancer risks multiply, Brenner and colleague Carl D. Elliston report in the September issue of Radiology. "The risks from a single full-body CT scan are not large: If 1,200 45-year-old people got one, you might expect one to die from radiation-induced cancer," Brenner tells WebMD. "But if you are thinking of doing this on a regular basis, as a routine screening modality, then the radiation doses start to add up and the risks then start to get quite high." A single full-body CT scan gives a person a total radiation dose of about 12 mSv. That's close to the 20-mSv dose linked to cancer in Japanese survivors of atomic bombs. And each of these scans adds another 12 mSv to a person's total lifetime exposure. An mSv is a unit for measuring radiation dose, observes CBS News.