Crisis or Opportunity? Tc-99m Shortage May Open the Door for More Imaging Options

Uncertainty about the supply of the radiopharmaceutical tracer isotope technetium-99m (Tc-99m) has cardiologists exploring a variety of options for imaging.

Uncertain future

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.

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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.

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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 widely available than Tc-99m. Historically used in oncology, PET offers better image resolution than SPECT and can help cardiologists reduce the number of patients who need invasive secondary exams because their SPECT results weren’t conclusive. PET also permits shorter exam times and reduces radiation by as much as a third.

“The accuracy of cardiac PET is better because it gets rid of a lot of the inherent artifacts we see in SPECT,” says Steven Silver, MD, a noninvasive cardiologist and head of the nuclear laboratory for The Heart House, a group of 27 cardiologists who work with eight New Jersey hospitals in five health systems. Citing true-positive rates of 85 percent or higher for PET vs. 70 percent for PET, Silver considers PET to be the more accurate screening tool for detecting coronary artery disease. “Anything we can do to minimize the false-positive rate is obviously very beneficial to patients,” he says.

The economics of cardiac PET are a substantial obstacle for many practices. Not only does the equipment cost more to purchase and operate compared with SPECT, but the expense to patients can be significant. Silver says the “biggest roadblock practices have [with cardiac PET] is trying to get beyond the logistics of insurance companies.” He predicts cardiac PET will not be affordable for most patients until payers determine that they “may pay a little more for PET than SPECT but the significant accuracy of the exam leaves less patients going to the cath lab, which is a huge cost [to payers] and a small but real risk to the patient.” 

Grewal appreciates cardiac PET’s advantages—including its shorter exam times and image accuracy—but says adoption may be limited to very busy practices and academic research settings. OhioHealth’s one cardiac PET scanner is located in an outpatient center. They may add more cardiac PET imaging in the future, but for now Grewal hasn’t embraced it because of the practice’s patient mix, the expense to patients and the organization, and PET’s inability to provide the “real-world analysis of exercise stress.”

Balancing act

Despite its challenges, SPECT isn’t going away anytime soon, says Josh Ginsberg, MBA, executive director of The Heart House, where Silver practices. The practice maintains five SPECT cameras and one PET scanner across six offices, and he’s evaluating whether to add a second PET scanner. He’s aware that reduced Tc-99m production could affect the practice’s ability to schedule normal routine SPECT tests in the future, but for now the possible shortage is not changing how the practice is managed, although he says the nuclear cardiology team is “constantly forward thinking about alternatives, most likely of isotope vs. modality.”

Physician preferences aside, Ginsberg sees cardiac PET continuing to be used more as a complement than a replacement for SPECT. By taking advantages of PET’s ability to penetrate larger body types with fewer artifacts than SPECT, his practice has used PET with patients who have a large chest or a body mass index over 40. They have seen a 15 percent reduction in cases requiring a secondary invasive exam when PET was performed.

“The patient experience is paramount to everything we do,” Ginsberg says, and that includes advocating for patients with their insurance companies and while scheduling tests. Factoring in the patient’s tolerance for SPECT’s longer exam time vs. PET’s requirement of holding the arms above the head while lying motionless in a confined space is one example of a practical issue they consider. Schedulers also try to accommodate how far patients need to travel to reach an office with a SPECT vs. a PET camera.

“Some patients do well within the PET scanner, and some do not,” Ginsberg says. Likewise, some patients, especially the elderly, may be challenged to get a ride to an office with a PET camera, which is likely to be farther away from a SPECT imaging facility. The goal is to strike the right balance for each patient, but ultimately, the policies of the patient’s insurance carrier will determine whether cardiac PET is even an option, he says.

Accuracy, radiation exposure and cost are among the many variables that cardiologists need to weigh when recommending imaging tests for patients, Grewal explains. “There is not one perfect modality, and that is why there are so many options.” 

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