Radiation: are we putting our health at risk with increased CT scans?

Brain scan

The number of CT scans in the UK rose by 68 per cent between 1998-2008

Tesco provoked an outcry by offering Clubcard members the opportunity to redeem points for a CT scan. Now, increasing numbers of scans in NHS and private hospitals are causing concerns that we are over-exposing ourselves to radiation

The UK population is receiving almost a quarter more medical radiation than it did a decade ago, according to the most recent report from the Health Protection Agency.

Looking at a sample 29 NHS Trusts in England, the report reveals that the dose per head of the population was 0.33 millisievert (mSv) in 1997/98, rising to 0.4 mSv in 2008, an increase of 23 per cent. An estimated 46 million NHS and private medical and dental x-rays were carried out in 2008, a 10 per cent rise over 10 years.

The increase is due in large part to the use of computerised tomography (CT), with the number of CT scans rising by 68 per cent over the same period. Conventional radiographic and fluoroscopic x-rays contribute only 19 per cent to the collective dose, despite constituting 90 per cent of all examinations. Certain CT scans can be up to 400 times more powerful than a chest x-ray.

Used originally in a clinical environment for head imaging in 1974, CT scanners work by sending several x-rays through the body simultaneously, which are then used to create two-dimensional cross-sections of the body and virtual images. Whole-body systems were introduced in 1976 and became widespread in the 1980s. There are now roughly 500 in the UK, 6,000 in the US and 30,000 worldwide.

They allow doctors to inspect the inside of the body without invasive examinations or operations, pinpointing tumours and helping in the planning of radiotherapy treatments.

Unnecessary scans

But such accuracy has led to its abuse by commercial interests, especially in the US, tapping into health fears by promising early diagnosis of disease.

‘I’ve seen some horrific adverts in the US for health clinics where the worried well – healthy people – can pay £5,000 for a whole body scan to put their minds at rest,’ says Professor Paddy Regan of the department of physics at the University of Surrey. ‘That’s a dangerous thing. CT is incredibly useful as a diagnostic tool, and the technological developments that give us good quality medical images using much smaller doses is something to be positive about, but the use of radiation-based imaging for healthy people is a risk people don’t need.’

The Twelfth Report, produced by the HPA for COMARE, noted in 2007 that while more than 90 per cent of CT scans were undertaken on the NHS, ‘there appears to be an increasing trend for commercial CT scans to be offered to the general population’. It added that medical exposures account for over 97 per cent of the annual dose to the UK population from artificial sources of radiation.

Tesco Clubcard scandal

In 2009 even Tesco was offering its Clubcard members the opportunity to redeem points for a CT scan, but stopped following a major outcry from health professionals. COMARE’s recommendations have now been adopted by the government, which has since clamped down on similar ‘MOT scans’.

In fact, the UK has some of the strictest radiation regulations in the world, with exposures tightly legislated, according to David Sutton, head of Radiation Physics at the Medical Physics department of Ninewells Hospital, Dundee.

All radiological procedures in the UK are governed by the Ionising Radiation (Medical Exposure) Regulations (IRMER) 2000, a regulatory framework that ensures all examinations are justified and signed off by a radiologist, with hospitals regularly audited to ensure all procedures are in place.

‘The overriding concern in the UK is that the benefit of the radiation outweighs the risk – if someone has a cancer with metastatic disease then CT can be used to identify its progression, and then again to identify how the patient’s drug regimen is working. Modern CT enables you to do that effectively and relatively quickly. Its accuracy also means further x-rays or other investigations may become unnecessary. So while there may be a dose associated with CT, patients also avoid the morbidity associated with the exams that they are no longer having.’

Natural exposure

Paddy Regan agrees: ‘A 23 per cent rise sounds dramatic, but the total increase in dose – from 0.33 to 0.4 mSv – is still only a tenth of what you get simply walking around. The typical UK citizen gets an annual dose of background radiation of around 3 mSv. It’s statistically more risky holidaying in Cornwall, where naturally occurring uranium deposits give off radon gas, which is the biggest contributor to everyday environmental radiation that humans are exposed to.’

Many of the people having the treatments are ill anyway, so the actual increase in risk of a relatively small dose of radiation would not increase the overall risk statistically, he adds.

‘There will be some quantifiable effect in the probability of developing a hard cancer, associated with exposure to small levels of radiation, but you have to weigh that against the fact that 25 per cent of the population will develop a fatal cancer at some point anyway, regardless of exposure to radiation.’

Steve Ebdon-Jackson, head of the medical exposure department at the Health Protection Agency, is not surprised by the increase in the number of x-ray examinations being carried out, particularly CT scans.

‘We know that the application of CT to a number of conditions is increasing, and so too are the benefits to patients. It is realistic to imagine that the use of CT will continue to rise, though not the same extent. The concept of “safe levels” has no meaning where medical exposures are concerned, since we don’t have a dose limit for individuals or populations, but as long as we continue to justify each individual exposure such that the benefit outweighs the detriment then I don’t see that we have too much to worry about.’

Useful links

HPA radiation report

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