Radiation from X-rays in dentist surgeries and hospitals causes 700 people in Britain to develop cancer each year, researchers say today.
Although medical X-rays help diagnose disease, they have long been known to cause a small increase in the risk of cancer because of the radiation they emit.
X-rays are the largest man-made source of radiation to which the public is exposed, accounting for 14 per cent. Atomic testing and discharges from nuclear power stations account for a fraction of that figure, and most of the rest is natural radiation such as radon from granite rocks.
Researchers from Oxford University and Cancer Research UK estimated the size of the risk based on the number of X-rays carried out in Britain and in 14 other countries. According to their findings, published in the medical journal The Lancet, the results showed that X-rays accounted for six out of every 1,000 cases of cancer up to the age of 75, equivalent to 700 out of the 124,000 cases of cancer diagnosed each year.
The calculations were based on the cancer rates among Japanese survivors of the atomic bombs dropped on Hiroshima and Nagasaki during the Second World War.
The UK had a lower risk from medical X-rays than most of the other areas studied including Scandinavia, the Netherlands, Germany, Australia and Japan. In Japan 30 of every 1,000 cases of cancer are thought to caused by X-rays.
In the UK, the National Radiological Protection Board (NRPB) has monitored the doses of radiation used in X-ray examinations for more than a decade. Advancing technology has halved the dose used in X-ray examinations since the early 1990s but the board found a 20-fold difference between the doses delivered in different hospitals in its latest review.
Concern has focused on the growing use of Computed Tomography (CT) scans which take a series of X-ray pictures through the body and have revolutionised the diagnosis of cancer and other diseases.
But according to the NRPB a single CT scan involves a dose of radiation up to 1,000 times that of a chest X-ray.
Barry Wall, head of medical dosimetry at the NRPB, said: "CT scanning is expanding so rapidly. The images are so fantastic that not a lot of attention is being paid to the doses used."
In a commentary on the findings, two German specialists in radiology said that the authors did not consider the benefits of X-rays in their study and offset those against the risks. "Benefits include the earlier detection of cancers by radiological examinations and the possibility of early treatment," they wrote.
But they said up to 30 per cent of chest X-rays might not be necessary. They also said that unnecessary CT examinations could cause radiation exposure. "Those ordering radiological procedures should think carefully about the benefit for and the risk to their patients for each examination."Reuse content