Alternative sources of 99Mo on the horizon

The production of 99Mo without the use of highly enriched uranium (HEU) has become a goal for diagnostic nuclear medicine, and a number of approaches hold promise for achieving this objective, according to an article published in the February issue of the Journal of Nuclear Medicine.

Reactor-produced 99Mo has been the only source of 99mTc, a radioisotope used in an estimated 30 million diagnostic procedures each year, according to authors Maroor R. A. Pillai, PhD, of Bhabha Atomic Research Centre in Mumbai, India, and colleagues. Because of the risks of nuclear material proliferation, however, there has been a push to phase out use of HEU and switch to alternate sources of 99Mo and 99mTc.

The authors pointed to a number of alternate reactor-based 99Mo production options using low enriched uranium, such as target-fuel isotope reactors and aqueous homogenous reactors. Accelerator-based production of 99Mo and 99mTc, using photo-fission or accelerator-driven subcritical assembly, for example, provide other options.

Pillai and colleagues noted, however, that these alternatives are still years away from being routine. “These approaches are balanced on a fine line, with technical breakthroughs on the one hand and long-term economic viability on the other,” they wrote.

For reactor-based, non-HEU options, the authors wrote that production of (n, gamma) 99Mo is appealing because it can be produced in existing research reactors and 99mTc can be separated from (n, gamma) 99Mo inexpensively. “These reactors would require few design changes, and they have good geographic distribution around the world,” wrote Pillai et al.

Direct production of 99mTc may be the most feasible of the accelerator and cyclotron-based options, according to the authors. The catch here is, as with [18F]-FDG, a short half-life means immediate transport to the location of use is a must.

One barrier to the implementation of alternatives is the role of government subsidies, wrote the authors. Many research reactors that were originally funded by governments have been commercialized, yet continue to receive subsidies. These subsidies, argued Pillai and colleagues, cause new industry entrants to doubt the economic viability of alternative techniques of producing 99Mo or 99mTc.

“It is important to ensure the commercial success of technologies to provide 99Mo or 99mTc of required quantities and quality for nuclear medicine,” wrote the authors. “Otherwise, the current suppliers will move to more financially successful programs, a move that is already on the horizon as seen from their enthusiasm in developing PET-based alternatives to replace 99mTc radiopharmaceuticals.”