New Data Will Shed Light on Cancer Risk From Imaging

January 31, 2012

January 31, 2012 (New York, New York) — Several ongoing epidemiological studies, including one in the UK that should report within the next year, should help provide a better understanding of radiation-associated cancer risks from cardiac imaging, says one expert [1].

Penning a state-of-the-art paper on the topic in the February 7, 2012 issue of the Journal of the American College of Cardiology, Dr Andrew J Einstein (Columbia University Medical Center, New York) admits that while cardiac imaging is the source of a fifth of all radiation exposures today, doctors have very little handle on the exact risk this poses to patients.

We will be more concerned, less concerned, or equally concerned.

He explains that radiation is such a weak carcinogen in adults that a sample size of hundreds of thousands, if not millions, would be needed to provide robust calculations of cancer risk from medical radiation. Hence, the ongoing studies that should help shed new light on this risk are mostly in children who have undergone computed tomography (CT); children are at increased sensitivity to radiation-induced cancer, enabling such studies to be performed with much smaller sample sizes, he told heartwire.

As well as the UK study--evaluating a cohort of about 250 000 individuals under age 22 years--additional studies are ongoing in Ontario (275 000 children), Australia (150 000), Israel, and several European countries. And the International Agency for Research on Cancer is coordinating a European collaborative study, incorporating over a million children, called the Epidemiological Study to Quantify Risks for Paediatric Computerized Tomography and to Optimise Doses (EPI-CT), he notes.

"We'll get more data from these various studies that will allow us to adjust our risk estimates," he says. "We will be more concerned, less concerned, or equally concerned."

A Lot of Press Attention; People Are Concerned

Einstein says he has written the new paper because "people are very concerned, they want to know what the association of radiation with cancer is. The issue has gotten a lot of attention in both the professional and lay press recently."

The reasons for this are twofold, he observes. "We are seeing increased utilization of some procedures that have relatively high doses of radiation to the patient, and we are seeing a tremendous increase in volume of procedures." This is particularly true of the US and Japan, he says, although he observes that this is "a worldwide phenomenon in developed nations."

Increases in US Radiation Burden From Medical Imaging

Source 1980-1982 (%) 2006 (%)
Nuclear cardiology 1 10.5
Cardiac CT -- 2.8
Cardiac intervention -- 3.6
Vascular intervention -- 2.0
Medical X-ray/CT 11  
Noncardiac CT -- 20.5
Nuclear medicine 3.0 --
Other X-ray/fluoro/nuclear medicine -- 8.4

Einstein and other experts in the field acknowledge that the fear from cardiac imaging outpaces knowledge about the risks, an issue that was covered in-depth by heartwire journalist Reed Miller in a feature last year.

The bottom line is there are no strong data that currently relate ionizing radiation specifically from cardiac imaging to increased risks of cancer.

"The bottom line is there are no strong data that currently relate ionizing radiation specifically from cardiac imaging to increased risks of cancer," says Einstein.

In the new paper, he summarizes the evidence base underlying concerns about radiation exposure in cardiac imaging, including classifying radiation effects, explaining terminology used to quantify the radiation received by patients, and describing typical doses from cardiac-imaging procedures.

He goes on to discuss the available epidemiologic data, from studies of atomic bomb survivors, nuclear industry workers, and children exposed in utero to X-rays.

With risk-projection models developed by the US National Academies that incorporate these data "and reflect several evidence-based assumptions," cancer risk can be estimated and compared with the benefits from imaging, he observes.

He also discusses what the effect of patient comorbidities might be on cancer risk, as most studies assume a relatively healthy population, he says, "but when you are applying estimates to patients who've had bypass surgery, it's not a great assumption."

Tricks of the Trade Are Not Always Implemented

And while the new data from children are eagerly awaited to provide a better understanding of radiation-associated cancer risks, there are precautions that can be taken in the meantime, Einstein stresses.

"The advice is to follow fundamental principles of radiological protection, which is justification and optimization. Justification: a test should be performed only if the benefits outweigh the risks and costs, and it's the best possible option for the patient at the particular time."

There's a variety of tricks physicians can use to try to keep radiation dose as low as possible while ensuring good diagnostic information.

For optimization, it's important that the test is justified, he says, and then "you should try to perform it keeping radiation doses as low as reasonably achievable, while ensuring good diagnostic image quality. There's a variety of tricks physicians can use to try to keep radiation dose as low as possible while ensuring good diagnostic information."

Asked whether he believes physicians and other healthcare providers performing these tests are generally aware of these principles of radiological protection, he replies: "I would say now, in a general sense, many people are aware of these things. But it's another step from the awareness of a problem to optimally implementing approaches to address the problem."

Einstein has received research grants from GE Healthcare and Spectrum Dynamics.

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