Uncertainty about the supply of the radiopharmaceutical tracer isotope technetium-99m (Tc-99m) has cardiologists exploring a variety of options for imaging.
Despite the efforts of the nuclear cardiology imaging staff to be prepared, the Tc-99m ordered weeks ahead of schedule hadn’t arrived. Now they had a patient on the table, awaiting a single photon-emission computerized tomographic (SPECT) imaging test. The team moved to plan B, using a lesser-quality tracer to complete the test, generating images not up to their usual standard with the possibility of more-than-optimal radiation exposure to themselves and their patient.
This scenario unfolded in 2013, following a brief shutdown of a reactor in Chalk River, Ontario, that produces more than one-third of the world’s supply of Tc-99m. Unfortunately, dilemmas like this one could become more common in the coming years, says Victor Gorre, MBA, BS, RT(R)(MR)(CT), director of imaging at Advocate Illinois Masonic Medical Center in Chicago. Gorre works with the center’s head cardiologist to plan for capital expenditures and expects their cardiology department “to double or triple [its] cardiac imaging volumes over the next year.”
The supply of Tc-99—the radioisotope used in 80 percent of diagnostic nuclear medicine testing, including cardiac SPECT—is drying up because all five of the reactors that produce Tc-99m’s parent isotope (Molybdenum-99, or Mo-99) are more than 50 years old. Aging reactors mean more frequent shutdowns for maintenance and little certainty about their long-term output. In 2018, the licenses for the two Canadian reactors, including Chalk River’s, will expire, eliminating North America’s most logical source for Mo-99, whose 67-hour half-life limits the shelf life of Tc-99m to a mere 6 hours.
With supply shortages looming, the American Medical Isotope Act was passed in 2011 to support vendors’ efforts to produce Mo-99 and create alternative radioisotopes. Meanwhile, health systems are taking steps to reduce their demand for Tc-99m and use alternative imaging. Some experts say that physicians are turning what could be a catastrophe into an opportunity to reconsider their options for cardiovascular imaging, perhaps delivering improved patient satisfaction with clinical outcomes that are as good or better than SPECT.
SPECT still dominates, even as alternatives emerge
Despite interest in alternative imaging options, 15 million SPECT imaging procedures are performed annually. Cardiac SPECT is a “well-established, highly standardized test to detect significant coronary artery disease and to risk-stratify patients with regard to cardiac event-free survival,” according to the American College of Radiology 2016 Image Wisely initiative.
“The acute issues practices faced [in 2013 and 2014] regarding isotope supply have gotten better,” says Kanny Grewal, MD, cardiac imaging system chief for OhioHealth in Columbus, but the improvements haven’t dissuaded his group from exploring other imaging options. He expects the relative stability in Tc-99m supply to be short-lived. Although SPECT is still front and center in OhioHealth’s imaging toolbox, they recently made some changes, including purchasing the newest-generation nuclear SPECT camera. With costs ranging from $200,000 to $400,000, the new cameras “are able to use far less radiation than in the past as well as reduce isotope dosage by as much as half, dependent upon patient size,” Grewal says. The newer cameras also allow for a more flexible protocol and can shorten the length of a SPECT exam as long as the first set of stress images is normal. Overall, says Grewal, the new cameras have enabled his team to deliver a better experience for patients while rationing radioisotope usage.
Since joining OhioHealth in 1997, Grewal has seen a gradual shift away from nuclear imaging tests and toward a more customized approach based on patients’ specific circumstances. Stress echocardiography has become his team’s first choice for younger, ambulatory patients, and coronary computed tomographic angiography (CCTA) is replacing stress testing in the emergency department.
PET stands out
Not being dependent on a single imaging option is crucial, experts told Cardiovascular Business. Among a growing range of choices, cardiac positron emission tomography (PET) is rising to the top of the list for many cardiologists and radiologists. One advantage of PET is that it relies on the radioisotope rubidium-82, which is more