Doctors have assumed that standard x-ray technology, including CT (computed tomography) and angiograms, were safe because they used very low levels of radiation.
As a result, they are regularly used for routine screening and scans, and when you are recovering from a health problem.
But they are not safe at all, as researchers from McGill University Health Centre in Montreal discovered when they tracked 82,861 heart patients who had been assigned at least one scan following a heart attack.
Of these, 12,020 - around 15 per cent of the total - went on to develop cancer, with two-thirds of these being cancers around the abdomen and chest areas, where they had been screened.
The researchers say that doctors need to rethink the way they screen patients as current practices "may pose a population risk".
(Source: Canadian Medical Association Journal, 2011; doi: 10.1503/cmaj.101885).