Caution urged over CT scan radiation doses

BBC News reports on a sharp rise in the number of CT scans being performed, exposing people to the potential health risks of radiation.

However, as The Daily Telegraph says, it is not possible to calculate the cancer risk due to exposure to CT scans because there is a lack of data.

These media stories follow the publication of a report by the Committee on Medical Aspects of Radiation in the Environment (COMARE). COMARE has reviewed trends in the use of CT scans in the UK. The review weighs up the risk-benefit balance of using CT scans, and considers ways to obtain the best quality scan image while minimising the necessary radiation dose.

The COMARE report sets out good practice guidance, encouraging doctors to take a more “proactive approach” to protecting patients and reducing radiation doses.

The committee recommendations cover equipment and procedures already in place, but also note there are dose reduction features available on some of the newer CT scanning machines that should be considered when new equipment is purchased.

What is COMARE and why is it looking at CT scans?

The Committee on Medical Aspects of Radiation in the Environment (COMARE) is an independent expert advisory committee, set up in 1985 to assess the available evidence and advise the government on the health effects of any form of natural or man-made radiation.

This is the committee’s 16th major published report. It follows a request from the Department of Health to assess the data available on radiation exposure during CT scans. The report looked at whether radiation exposures were justified (whether the benefits of the CT scans outweighed the risks). It also looked at ways to optimise the benefits of CT scans while minimising the risk to patients.

What does COMARE’s report say about the use of CT scans?

We are exposed to many sources of radiation, with the majority of radiation exposure coming from natural, environmental sources. Figures from the US show that on average, each year in the 1980s, only 15% of radiation exposure came from medical sources (0.54 millisievert [mSv] per person per year) – the rest from natural sources. By 2006, radiation exposure coming from medical sources each year had leapt to almost 50% of total annual radiation exposure (2.98mSv).

By contrast, the UK’s less medically intensive culture means that only 15% of our radiation exposure comes from medical sources. However, it has still increased from 0.33mSv per person per year in 1997, to 0.4mSv in 2008.

CT scans account for much of this exposure. In the 1980s CT scans were only contributing around a quarter of the medical radiation dose in the UK, but this had increased to around two-thirds by 2008. The number of CT scans performed by the NHS in England each year increased from just over 1 million in 1996/97, to almost 5 million by 2012/13, with no sign of reaching a plateau.

The report says there has been wider use of CT scans among younger people and children, whose tissues may have greater sensitivity to radiation. They also, of course, have a longer lifespan ahead of them in which potential harmful effects may be observed.

How do the risks and benefits of CT scans compare?

A CT scan is a special type of X-ray that produces very accurate cross-section views of the inside of the body.

The COMARE report highlights how CT scans can:

• improve diagnosis and staging of cancers
• reduce need for unnecessary “exploratory surgery” or other invasive examinations
• demonstrate response to treatments
• help the treatment of certain conditions, such as guiding biopsies and treatments for stroke or heart disease

However, it says that 70% of indications for CT scans recommended by guidance relate to benign (non-harmful) or potentially benign conditions. It says that CT scans are increasingly being used as a standard investigation, replacing other conventional ways of detecting health problems.

There are potential risks related to radiation. Radiation can cause immediate direct damage to body tissues (such as radiation burns and hair loss), although usually only when given at higher doses. More problematically, radiation is also recognised as a carcinogen. It could potentially be involved in the future development of cancers for the person being scanned, or potentially having genetic effects in any future children.

Overall, there is uncertainty about the level of risk from radiation from CT scans. The risk to anyone is influenced by many factors, including age and size, the part of the body being scanned, number of scans given and radiation dose, and the radiosensitivity and genetic susceptibility of the individual.

Studies to date examining radiation risk are often population-based studies that have not accounted for important factors such as the age or medical prognosis of that person, making it difficult to attribute radiation as the direct cause of any outcomes.

UK law means that medical radiation exposures for patients must be:

• “Justified” – exposure producing sufficient benefit to the exposed individual to outweigh the potential risk of exposing to radiation
• “Optimised” – procedures and techniques should be in place to keep radiation exposures as low as reasonably practical

What does the COMARE report recommend?

COMARE recommends encouraging a more proactive approach to protecting the patient and reducing radiation dose as part of its good practice advice.

It wants:

• the UK to be actively involved in further research into the risks of radiation
• Public Health England to undertake more frequent UK dose surveys to provide data to support regular updating of national diagnostic reference levels, including those specifically regarding children. COMARE advises the Department of Health to require healthcare providers to submit dose data for individual patients
• hospitals to consider CT scanners that have a full range of dose reduction features when buying new equipment
• the Department of Health to fund, if necessary, independent evaluation of CT scanners
• the Royal College of Radiologists to work to ensure that CT scans are optimised, taking into account both image quality and dose. This would mean requests for CT scans needing to include a clear statement regarding the clinical question to be answered by the scan
• the Royal College of Radiologists and other appropriate organisations to review and produce referral guidelines that give greater emphasis on alternative imaging techniques that use less or no ionising radiation