Cardiovascular Nuclear Imaging: Balancing Proven Clinical Value and Potential Radiation Risk

The debate on the potential risk of radiation exposure from diagnostic imaging tests highlights the importance of balancing the demonstrated clinical benefit and the theoretic risk of cardiovascular imaging studies. The Cardiovascular Council of the Society of Nuclear Medicine upholds the responsible application of imaging studies that use radiotracers associated with relatively small amounts of ionizing radiation. Radionuclide-based cardiac imaging studies, including myocardial perfusion imaging (MPI), provide accurate diagnostic and prognostic information about patients with suspected or known heart disease. There is a large body of scientific evidence on the clinical value of MPI, based on studies performed on many thousands of patients. On the basis of this information, appropriate-use criteria and guidelines were developed and endorsed by the Society of Nuclear Medicine and other professional societies, including the American College of Cardiology, American Heart Association, and American Society of Nuclear Cardiology (1). Cardiovascular nuclear medicine studies provide highly sensitive and specific tests that may be indicated for the evaluation of diagnosis, prognosis, and treatment response of coronary artery disease, as well as for selection of patients who benefit from revascularization. The value and justification of MPI for risk assessment is based on large observational outcome studies that demonstrate accurate risk stratification with radionuclide-based MPI in populations with an intermediate pretest risk. The incremental prognostic value of SPECT MPI is greater than that of the exercise electrocardiography stress test or coronary angiography. The cost effectiveness of MPI as a gatekeeper to coronary angiography has been established after being carefully and extensively studied. Several recent publications have raised concern about the potential harmful effects of ionizing radiation associated with cardiac imaging. Review of the measurement of radiation and associated biologic effects can help put this issue into reasonable perspective. Radiation effective dose is a measure used to estimate the biologic effects of radiation. Measuring the radiation effective dose associated with diagnostic imaging is complex and imprecise and often results in varying estimates among experts (2). A typical effective dose for a rest–stress same-day SPECT scan using 99mTclabeled agents (1,110 MBq [30 mCi] stress, 370 MBq [10 mCi] rest), the most commonly used MPI protocol, is approximately 10 mSv. Other agents and protocols are associated with a wide range of radiation exposure (2). In comparison, exposure to radiation from natural sources amounts to approximately 3 mSv annually. The risk of a fatal malignancy from medical imaging–related radiation is difficult to estimate precisely but is likely small and difficult to discern from the background risk of natural malignancies. The theoretic lifetime attributable risk of cancer from a rest and stress 99mTc-based MPI study for individuals age 35 y or older is less than 1.5 in 1,000 (3). This risk is less in older patients, who constitute most patients evaluated for coronary artery disease. The estimated risk of fatal malignancy from a typical MPI study is 0.5 per 1,000 individuals, compared with a risk of death from natural cancer of 212 per 1,000 (4). The potential risk of cancer must be balanced against the risk of death, myocardial infarction, or other morbid vascular events in an appropriately referred population. This risk ranges from 1% to 10% or more per year and is orders of magnitude greater than the potential lifetime risk of cancer and death from cancer attributable to cardiovascular nuclear medicine studies. Assessment of risk-to-benefit ratio mandates a good understanding of the clinical characteristics of the patient, including risk factors for coronary artery disease, prior history of coronary artery disease, and left ventricular function. For example, given the substantially higher risk of morbid coronary events or heart failure in patients with left ventricular dysfunction, higher radiation exposure associated with 201Tl or 18F-FDG for radionuclide assessment of viability is readily justifiable. In this context, one must not fail to take into account the risks of missing important diagnostic information by not performing a test (which could potentially influence near-term management and outcomes) because of a theoretic concern about a long-term small risk of malignancy. Similarly, assessment of the significance of radiation exposure risk in population-based studies would be challenging without information on the overall pool from which the patients are selected and how representative they are of the total patient population. While the potential long-term radiation risk associated with cardiovascular nuclear medicine studies is debated (5), Received Mar. 17, 2011; revision accepted Mar. 24, 2011. For correspondence or reprints contact: Mehran M. Sadeghi, Yale University School of Medicine, 950 Campbell Ave., West Haven, CT 06516. E-mail: mehran.sadeghi@yale.edu COPYRIGHT a 2011 by the Society of Nuclear Medicine, Inc. DOI: 10.2967/jnumed.111.090654