Radiation from X-rays and CT scans DOESN'T cause cancer

Countless scientific studies have debated the issue - does radiation from X-rays and CT scans cause cancer?

At very high doses the evidence is clear, scientists say - the answer is yes.

But one oncologist from Loyola University in Chicago now points to 'serious flaws' in the theory, when considering everyday exposure to radiation during medical scans.

Dr James Welsh said the reliance of past research on unproven statistical models is important.

'Although radiation is known to cause cancer at high doses and high-dose rates, no data have ever unequivocally demonstrated the induction [start] of cancer following exposure to low doses and dose rates,' said Dr Welsh, and his co-author Dr Jeffry Siegel.

They argue studies that have identified a link between medical imaging and cancer, typically use a model known as 'linear no-threshold' (LNT).

In LNT, the well-established cancer-causing effects of high doses of radiation are simply extrapolated downward in a straight line to low doses.

The LNT model assumes there is no safe dose of radiation, no matter how small. 

But although LNT is used by regulators around the world, the model is 'of questionable validity, utility and applicability for estimation of cancer risks,' Dr Welsh and Dr Siegel said. 

Contrary to the LNT model, there is compelling evidence that the human body has evolved the ability to repair damage from low-dose radiation. 

For example, the mutation rate caused by low-dose background radiation in the environment is 2.5 million times lower than the rate of spontaneous mutations in the body. 

So even if the LNT model were true, the small increase in mutations caused by low-dose radiation from medical imaging would be unlikely to overwhelm the body's defences.

They add studies purporting to find a cancer link to medical imaging radiation have other flaws besides the questionable LNT model. 

For example, Dr Welsh and Dr Siegel highlight, two recent studies suggested possible increased cancer risks from low-radiation doses associated with paediatric CT scans. 

But these cancers are likely due to the medical conditions that prompted the need for a CT scan, rather than the radiation exposure, the pair noted.

While many people focus on the apparent risks of radiation in medical imaging, 'the more significant and actual risks associated with not undergoing an imaging procedure or undergoing a more invasive exploratory surgery are generally being ignored in both the scientific literature and the popular media,' they added.

The views first appeared in the journal Technology in Cancer Research & Treatment.

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