CT scans can be a public health time bomb
The current media stories in Australia about radiation exposure from CT scans echo those that have recently played out in the US in both the medical and public media.
By Dr Lesley Russell
The current media stories in Australia about radiation exposure from CT scans echo those that have recently played out in the U.S. in both the medical and public media.
A paper published last August in the New England Journal of Medicine studied nearly one million non-elderly Americans to estimate their radiation exposure from medical imaging. Though the annual average radiation exposure was small for most people (less than 3 millisieverts), about 20% in the study had moderate exposure (3 to 20 millisieverts) and 2% had high exposure (20 to 50 millisieverts).
Given these findings, the researchers estimated that medical imaging exposes four million non-elderly Americans to high-level doses of radiation (more than 20 millisieverts) every year. These sorts of exposure levels are certainly high enough to cause cancer.
A study presented at the American Heart Association’s Scientific Sessions in Florida in November 2009 showed that acute heart attack patients admitted to academic hospitals received an average total dose of ionising radiation of 14.5 millisieverts (equal to 725 chest x-rays) from medical tests during their hospital stay. It’s quite easy for a patient undergoing a series of tests quickly to accumulate doses even higher than this.
The average life-time dose of diagnostic radiation for Americans – excluding therapeutic radiation - has increased sevenfold since 1980. In large part this is due to the sharp rise in the number of CT scans - now close to 100 million are done every year. It is estimated that up to one-third of these scans may be unnecessary. Although CT scans make up only 12% of all medical radiation procedures, they deliver almost half of the estimated collective dose of radiation exposure. Nuclear medicine procedures, which have increased more than three-fold in the past 25 years, represent almost a quarter of the estimated collective radiation dose. Even traditional X-rays can contribute to a person’s cancer risk.
A 2009 study from the National Cancer Institute published in Archives of Internal Medicine found a 13-fold range between the highest and lowest actual radiation doses delivered for CT scans on the same body part.
And sometimes the machines and their increasingly sophisticated computer systems are faulty and this is not recognised by the operator. Over the past 10 years more than 1,000 reports of known over-doses, under-doses and other errors have been reported to the US Food and Drug Administration (FDA).
With those scary statistics on the table, it’s important to note that Australia is not the US – and certainly not when it comes to CT scans. For starters, it’s quite common in the US for doctors’ practices to have their own CT scanners, and to use them often, with little regard for (or knowledge of) patients’ previous scans. Sometimes this is done simply because the doctor is practising defensive medicine - after all, that headache might be a brain tumour.
Secondly, with the exception of mammography, which is subject to Federal standards, scans remain largely unregulated. The FDA regulates the imaging equipment but does not inspect imaging facilities, which are licensed by the States. There is no mandatory accreditation of imaging facilities and no minimum standards for personnel who operate them.
The FDA has now said that it will use its regulatory muscle to ensure the safety and oversight of medical radiation, something the agency has been reluctant to do in the past.
The FDA will no longer allow new radiotherapy equipment to enter the market via an abbreviated approval process that requires minimal scrutiny, pays little attention to technological advances and sometimes involves the use of outside, third-party reviewers. Last year 40% of new radiotherapy equipment was approved through this streamlined process. This will have an impact in Australia, given that most Australian CT equipment is purchased overseas. (See “USFDA gets tough, but still not tough enough”, page 38.)
Perhaps the main lesson for Australia from the US experience is that, just because CT scans are quick, painless and give patients and their doctors the satisfaction that everything has been done, it does not mean they are without negative side effects, especially for younger patients. A single CT scan can deliver the same radiation dose that survivors of the atomic blasts at Nagasaki and Hiroshima endured. Doctors and patients cannot be complacent about the hazards of radiation or they risk creating a public health time bomb.
Dr Russell is the Menzies Foundation Fellow at the Menzies Centre for Health Policy, The University of Sydney/Australian National University, and a Research Associate at the US Studies Centre at The University of Sydney. She is currently a Visiting Fellow at the Center for American Progress in Washington, DC.
Reza Fazel et al. (2009) Exposure to Low-Dose Ionizing Radiation from Medical Imaging Procedures. NEJM, 361:849-857. Available at http://content.nejm.org/cgi/content/short/361/9/849
Rebecca Smith-Bindman et al (2009). Radiation dose associated with common computed tomography examinations and the associated lifetime attributable risk of cancer. Arch Intern Med,169:2078–86. Available at http://archinte.ama-assn.org/cgi/content/abstract/169/22/2078
Published: 02 May 2010