"We want to reassure the public that for individual patients the benefits of receiving an accurate diagnosis are likely to far outweigh the small potential risks involved in having a scan,” said Prof. Juhani Knuuti, of the ESC (European Society of Cardiology; Sophia Antipolis, France) Working Group on Nuclear Cardiology and Cardiac CT, from Turku University Hospital (Turku, Finland). "The most fundamental question that clinicians need to ask themselves is whether a test is appropriate for the individual patient, and whether that patient will derive benefit from it.”
It needs to be remembered, Prof. Knuuti added, that tests such as cardiac computed tomography angiography (CCTA) are used to select patients for invasive procedures that themselves carry risks. "Any procedure is a balance of risks and benefits. What has been overlooked in recent publications is the risk of cardiovascular disease going untreated, which can even result in immediate sudden death. The potential risks of imaging tests are small relative to the diagnostic information obtained,” said Prof. Knuuti. "We have real concerns that following the publicity around the [research], the public may avoid these tests out of fear and that authorities might create unjustified recommendations for imaging use. They need to appreciate that radiation is a single aspect of the risks involved, and that these are really useful tests for cardiologists. Everything needs to be considered in the wider context.”
In 2009, the problems of radiation exposure in patients undergoing medical imaging procedures were raised in three articles in major journals. A Science Advisory statement from the American Heart Association Committee on Cardiac Imaging wrote that between 1980 and 2006 the collective dose from medical uses of radiation received by the US population increased by more than 700%. The study added that in 2006 CTTA accounted for around 50 % of the collective dose.
A study conducted, by Reza Fazel and colleagues, from Emory University School of Medicine (Atlanta, GA, USA), reviewed the radiation exposure of nearly one million US adults aged 18 to 64. The investigators found that 69% of participants had undergone at least one imaging procedure associated with radiation, and that the mean cumulative dose was 2.4 mSv per subject per year. "Our finding, that in some patients worrisome radiation doses from imaging procedures can accumulate over time, underscores the need to improve their use,” reported the investigators, adding that strategies for optimizing and ensuring appropriate use of the procedures in general should be introduced.
A study performed Jorg Hausleiter and colleagues, from Klinik an der Technischen Universitat, (Munich, Germany) reviewed the radiation dose of CCTA from 50 study centers. Results revealed an estimated median radiation dose corresponding to 12 mSv, and furthermore found a six-fold difference in the dose delivered between the highest and lowest centers. "Improved education of physicians and technicians performing CCTA on these dose-saving strategies might be considered to keep the radiation dose 'as low as reasonably achievable' in every patient undergoing CCTA,” concluded the authors.
"It is important,” said Prof. Knuuti, for the public to try to achieve an understanding of exactly what the potential increased cancer risk might involve. "The difficulty involved here is that the risks are so small that you'd never be able to detect them in clinical trials unless you recruited millions of subjects and followed them for the rest of their lifetimes,” he stated, adding that the current risk estimates have been derived from studies of atomic bomb survivors.
One study that helps put the risk of imaging into perspective suggests that living with a smoker (i.e., being a passive smoker) causes a 20 times higher risk of fatal cancer than undergoing one CCTA scan (10 mSv). Another study suggests that the risk of having a fatal pedestrian traffic accident is three times higher than the risk of developing fatal cancer after one CCTA scan.
Cancer risks also need be considered in relation to the patient's age at the time of undergoing the investigation. "For patients with chest pain over the age of 60 years the radiation risks involved are unlikely to have consequences since it takes anyway decades to develop potential adverse events,” stated Prof. Knuuti, adding that the estimated risks would be greater for younger patients.
The next step, according to Prof. Knuuti, is to introduce strategies that reduce the radiation dose received by patients undergoing investigations. The PROTECTION 1 study, for example, showed that reducing the tube voltage from 120 kV to 100 kV resulted in a 53% reduction in the median radiation dose for CCTA. "In the last five years the radiation dose from CCTA has been reduced from 20-30 mSv to 1-5 mSv. So the current dose is much lower than these papers are leading us to believe,” he added.
Furthermore, additional efforts need to be undertaken to ensure appropriate use of imaging tests in different patient populations. "Studies undertaken in the US have suggested that one third of tests are being undertaken in patients where there is not a good indication,” concluded Prof. Knuuti.
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