Medical treatments are being delayed or deferred at hospitals worldwide because of the extended shutdown of a Canadian reactor.

The reactor, the Atomic Energy of Canada reactor at Chalk River, Ontario, near Ottawa, is North America’s only source of the base isotope for technetium-99, a workhorse of modern medical diagnostic systems. It is injected into patients 20 million times a year in the United States to create images used in the diagnosis and treatment of a wide variety of illnesses including heart ailments, cancers and gallbladder problems.

Because the isotopes created by the reactor decay rapidly, they cannot be stockpiled, which is leading to growing shortages of the material at medical centers. Adding to the problem is the fact that the Atomic Energy reactor produces 50 to 80 percent of the world’s supply of molybdenum-99, the isotope that breaks down into technetium-99.

Like disposable flashlight batteries, however, the generators eventually run down. The Atomic Energy reactor shutdown has left some hospitals unable to find replacements.