Global supplies of an isotope used in medical diagnostic imaging will fall substantially when a Canadian reactor stops producing it at the end of October, according to a report released today by the National Academies of Sciences, Engineering, and Medicine. Nearly all of the world’s supply of molybdenum-99 is produced by seven research reactors in Australia, Canada, Europe and South Africa. The isotope is distributed through an international supply chain at least weekly because it cannot be stockpiled. “Current efforts to increase the supply of molybdenum-99 by expansion of existing overseas production and initiation of domestic production by methods not requiring highly enriched uranium are important to ensure future availability,” said S. James Adelstein, chair of the committee that produced the report and a professor of medical biophysics at Harvard Medical School. “Although there are plans from both existing international suppliers and potential domestic suppliers to fill the expected supply gap from Canada, the committee is concerned that any delays in bringing additional supplies of molybdenum-99 to the market would increase the risks of substantial shortages.”