Switching tracers due to a shortage of technetium-99m (Tc-99m) may be more than an inconvenience for cardiac facilities and their patients. A before-during-after analysis from one center showed an increase in downstream testing, costs and radiation exposure with the temporary use of thallium-201 (Tl-201).

The University of Ottawa Heart Institute in Canada was among the facilities that turned to Tl-201 after a the 2009 shutdown of the Canadian Chalk River nuclear reactor in Ontario led to a shortage of Tc-99m. The aging reactor is expected to close in 2016 and potentially could experience an unscheduled outage at any point. Until additional resources become available, physicians who perform SPECT MPI studies to diagnose and assess coronary artery disease (CAD) face the possibility of having to once again use Tl-201 as a radiotracer.

The heart institute’s Gary R. Small, MBChB, PhD, and colleagues designed a retrospective study based on data from 7,402 consecutive patients referred for MPI that spanned before, during and after the facility’s switch from Tc-99m to Tl-201. The results were published online July 19 in Circulation: Cardiovascular Imaging.

Patients were grouped as pre (2,938 who underwent studies with Tc-99m), during (2,959 patients who underwent studies with Tl-201) and post (1,505 patients, TC-99m). The study period covered May 2008 to January 2011.  

They collected data on downstream invasive cardiac catheterizations, coronary CT angiography, cardiac PET, stress echocardiography and coronary revascularization rates. Patient records were analyzed for six months after the index SPECT MPI. They then calculated rates and results for downstream use, radiation dose estimates and costs based on the 2012 Medicare reimbursement fee schedule.

Patient demographic characteristics, pretest probabilities for coronary disease and frequency of reported symptoms of CAD were similar for patients in the Tl-201 group and the Tc-99m groups.

 According to the results:

• 21.4 percent of patients in the Tl-201 group underwent downstream testing compared with 12.1 percent in the Tc-99m groups, a trend that held in a subgroup analysis for suspected vs. documented CAD;
• False positives were more common in the Tl-201 group than in the TC-99m groups (30.3 percent vs. 16.4 percent);
• The increased per-person cost from downstream procedure was $165.22 for Tl-201 vs. $90.97 for Tc-99m;
• Radiation exposure for the SPECT study alone was 19.89 mSv for Tl-201 vs. 10.44 mSv for Tc-99m; and
• The effective per-patient dose for downstream tests using radiation was 3.68 mSv with the Tl-201 group vs. 2.48 mSv with the Tc-99m groups.

“[Tl-201 use] was associated with a significant increase (9.8 percent) in downstream resource utilization amounting to a cost increase of $74.25/patient. Extrapolating this number to the 9 million SPECT MPIs performed annually in North America, the potential incremental cost implications could be $668 million annually,” Small et al wrote, adding that the estimate was conservative because it did not include the cost of physician visits, consultations, lab work and societal costs. Their extrapolations on radiation exposure also suggested 4,766 more cases of fatal malignances.

The researchers noted that was an increase in false positives and decrease in specificity associated with Tl-201, which they suggested was probably due to differences in image quality.

As a single-center study, their findings may not be generalizable to other centers.