Radiation Exposure from Cardiac Imaging Underestimated

Many physicians greatly underestimate the amount of radiation patients are exposed to during the most commonly administered tests, according to a recent literature review [Eur Heart J. DOI:10.1093/eurheartj/eht394].

Increased awareness and knowledge are vital to decreasing exposure. This year, the nuclear cardiology community is aiming for an average total radiation exposure of <9 mSv in half of the single-photon emission computed tomography (SPECT) and positron emission tomography (PET) studies that are performed.

Luigi P. Badano, MD, FESC, FACC, University of Padua, Padua, Italy, and colleagues at the European Society of Cardiology Associations of Cardiovascular Imaging, Percutaneous Cardiovascular Interventions and Electrophysiology, conducted a literature review to summarize current knowledge on radiation effective doses and risks with regard to cardiac imaging.

Cancer risk has increased when radiation exposure is in excess of 50 mSv. Today, it is not uncommon for a patient to reach doses of 50 mSv to 100 mSv in a single hospital admission or within a single imaging exam. Women and children are at a particularly increased risk. The additional risk of cancer associated with this excess radiation exposure is estimated to range from 1 in 30 to 1 in 300.

Nuclear Medicine

Nuclear cardiology accounts for more than 50% of all nuclear medicine procedures and 85% of the entire cumulative exposure due to nuclear medicine. The exposure associated with nuclear medicine procedures (eg, PET and SPECT scans) generally ranges from 2.4 mSv to 40.7 mSv.

The researchers estimate that this exposure can be decreased by 75% if physicians use a protocol involving the use of stress imaging as a first step and eliminating rest images in patients with normal stress images.

Additionally, the researchers found a 15% rate of dual radioisotope testing, which generates exposure of approximately 30 mSv. SPECT detectors that utilize cadmium zinc telluride technology can decrease radiation exposure while preserving image quality.

Computed Tomography (CT)

Although the use of CT scans has increased drastically over the past 20 years, the dose administered per exam has decreased. In the past decade, the radiation dose has been reduced by three-fourths thanks to more dose-saving measures and evolving scanner technology. Manufacturers continue to find ways to reduce radiation exposure, while maintaining images that provide sufficient diagnostic quality. If a patient’s heart rate is adequately slow and regular, cardiac CT angiography can be performed in a manner that produces high-quality diagnostic images with a mean effective radiation dose of less than 2 mSv.

Interventional Cardiology/Electrophysiology

Fluoroscopically guided diagnosis and intervention comprise 12% of all radiologic examinations performed in adult cardiology patients and 48% of their total collective dose. The amount of radiation exposure varies widely, from about 5 mSv for thoracic angiography to between 76 mSv and 119 mSv for an endovascular thoraco abdominal aortic aneurysm repair procedure.

The advent of nonradiology based methods of cardiac mapping, along with the use of coregistration of CT or cardiac magnetic resonance images of target structures, such as the left atrium, have the potential to greatly reduce exposure.

Exposure to Practitioners

Interventional cardiologists and electrophysiologists are reportedly exposed to doses of about 5 mSv each year, a rate 2 to 3 times greater than diagnostic radiologists. Adequate radiation protection, can reduce exposure by 90%.

Increasing Awareness

The researchers assert that an informed consent form should specify the specific reference dose, and, following the procedure, the delivered dose should also be recorded in the patient and the laboratory records. Patients should be provided with dose information if they desire; this is already required and enforced by law in some countries. This process should aid in reinforcing the practitioner’s knowledge and assist them in making more responsible choices.

Dr. Badano concluded, “It is mandatory that clinical and interventional cardiologists make every effort to reduce unnecessary radiation exposure from medical imaging. Tests involving ionizing radiation should only be performed if the information required cannot be obtained through tests that do not involve ionizing radiation. If a test that utilizes ionizing radiation has to be performed, the smart cardiologist will choose the one with the lowest radiation dose, being aware of the many factors modulating dose. Scientific societies should not fight against radiological imaging, which is often essential and life-saving, but they must fight against the unawareness of doses and related risks.”