As major research reactors supplying molybdenum-99 (Mo-99) are aging and ceasing production, scientists supported by the International Atomic Energy Agency (IAEA) are pursuing an alternative production method to help increase the supply of this key isotope used in nuclear medicine to provide essential healthcare to millions of patients worldwide.
In 2009, reactors producing Mo-99 in Canada and the Netherlands were temporarily shut down for necessary repairs and maintenance. This caused a major disruption in healthcare services worldwide, leading to cancelled medical scans, postponed operations and, in some cases, required reverting back to old, less effective techniques. While supply conditions have since improved, health officials and scientists have been looking into alternatives to address what a recent U.S. National Academies report called “supply vulnerabilities”.
“This disruption was really a wake-up call that something needed to be changed in how we are producing Mo-99,” said Danas Ridikas, Research Reactor Specialist at the IAEA. “Diversification of how and where Mo-99 is produced, increasing efficiencies in the way the isotope is used, and devising a business model to recover production costs have become essential to ensure a continued, stable and economically viable supply of Mo-99.”
Mo-99 is the parent isotope of technetium-99m (Tc-99m), the most widely used radionuclide for medical imaging. Because Tc-99m is unstable and decays quickly, its more stable parent isotope is produced and transported to hospitals.
With a research reactor in Canada ceasing production in October 2016, and another large producer in the Netherlands scheduled to go offline by 2024, finding alternative production methods are becoming more critical, Ridikas explained. Producing Mo-99 by irradiating natural or enriched molybdenum is one of the lesser-used yet viable alternatives to fulfil domestic needs, in particular for countries with research reactor facilities, he said.
The new method, already in use in Chile, India, Kazakhstan, Peru, Russian and Uzbekistan, involves a simpler production process and generates less radioactive waste than the traditional method of producing Mo-99 through fission from uranium. In addition, it can improve the utilization of research reactors. Several countries, including Jordan, Mexico and Morocco, are considering implementation of the technique.
While the new method shows potential, experts are still evaluating its efficiency. In December 2015, an IAEA workshop on the subject brought together experts from 15 research reactor facilities in 12 countries to explore the method and its feasibility. Experiments to irradiate natural molybdenum targets, carried out in several research reactors with IAEA support, clearly showed that the Mo-99 obtained through irradiation produced less Mo-99 per gram of material irradiated than the fission method. However, the amount obtained should still be sufficient to meet local needs in several countries.
Irradiating enriched molybdenum would yield a higher ratio of Mo-99, but would require a more expensive raw material. Therefore, using natural molybdenum despite the lower yield may be more optimal, Ridikas said. “The cost-effectiveness of irradiation and processing, compared to the fission method, still needs to be determined.”
The lessons learned from the workshop and data on the approximate production capacities of the reactors formed the basis for a paper by Ridikas and several other scientists published recently in the Journal of Radioanalytical and Nuclear Chemistry. It also serves as a platform for continued research.
A related workshop on irradiated target processing and preparation of Tc-99m generators, based on Mo-99 production by neutron capture, will be organized by the IAEA in 2017 in Kazakhstan.
Article adapted from original by Jeremy Li, IAEA, edited for context and format by CBRNE Central.