CT scans

A new study on the risks to patients of CT imaging will be reviewed by Health Protection Agency experts as part of ongoing work.

Computed Tomography, or CT, scans use ionising radiation but help doctors create 3D images of internal organs, blood vessels, bones or tumours and in recent years have become valuable diagnostic tools.

A new US study, published in the journal Archives of Internal Medicine, which has been featured in a number of newspapers, found that radiation doses were generally higher than previously thought.

In the UK the Health Protection Agency, and before 2005 its predecessor body the National Radiological Protection Board, has the responsibility of advising Government on issues to do with the health effects of radiation.

Ever since it was created in 1970, staff at the NRPB have carefully monitored the way radiation is used in medical procedures and has advised on ways to reduce doses to patients.
In 1990 the NRPB published a paper in collaboration with the Royal College of Radiologists on reducing patient doses from radiological diagnostic tools and since then experts have carried out a number of reviews of technology used by medics, including CT scanning, which utilises ionising radiation.

Scientists and clinicians in the UK have long known that when using radiation there is a balance between the benefit of improved medical diagnosis and the detriment associated with ionising radiation - specifically the probability of cancer induction.

This is why the Agency considers it so important that each individual exposure is medically justified and why there is an ongoing programme at the HPA looking at radiation doses from CT imaging, and how they can be minimised.

This provides national reference doses to UK hospitals and a greater awareness of dose from CT in UK radiology departments.
Coupled with high standards of operator training, the Agency's scientists believe doses in the UK from CT tend to be lower than in many other countries including the USA.

The interest in dose from CT imaging in the USA is relatively recent and it should also be noted that practice also varies between the USA and the UK.

Nevertheless, as with the USA, there is a variation in doses administered from centre to centre for the same examination, and more significantly, the risk to the patient will vary depending on the size, age and sex of the patient.

The dose from a representative CT scan of the chest, abdomen and pelvis is about 10millisieverts (mSv) for UK adults giving an average risk of fatal cancer of 1 in 2000.
Scans of just the head or chest would give lower doses and lower risks. For older patients, on whom most CT occurs, the risks drop considerably.

The average person in the UK receives 2.2mSv a year from natural sources and 0.4mSv from medical sources. That is about eight times less medical radiation than the average American, according to the most recent estimates.

The frequency of CT examinations per head of population in the USA remains about 3.5 times higher than in the UK.
The highest risks quoted in the new American research are, say HPA scientists, only likely to occur in extreme circumstances, most likely when patients, probably children, are undergoing repeated examinations over a period of time to follow-up a life threatening condition.

As knowledge of CT doses has increased, medical equipment manufacturers have introduced dose reduction technology into their latest CT scanners.

More information on the use of radiation in medical procedures.

Last reviewed: 15 December 2009