David L. Shenkenberg, Features Editor, firstname.lastname@example.org
“Crisis” is a word that medical professionals and scientists rarely use because it smacks of sensationalism, yet that is precisely the word used by the Society of Nuclear Medicine of Reston, Va., to describe a recent shortage of radioisotopes.
The shortage is primarily of the molybdenum-99 radioisotope (Mo-99), which is formed in a fission reaction in a nuclear reactor. There is also a shortage of iodine-131, which is used for treating hyperthyroidism and thyroid cancer.
The Mo-99 shortage happened because of the shutdown of the Chalk River reactor in Ontario, Canada, and the Petten reactor in the Netherlands. Typically, these two reactors together supply more than two-thirds of the world’s Mo-99. Each year, more than 8 million patients in the US alone benefit from Mo-99 produced at Chalk River Laboratories.
Chalk River Laboratories is located on the banks of the Ottawa River in Ontario, Canada. Courtesy of Padraic Ryan and Wikimedia.
“With both the Chalk River and Petten reactors down at the same time, this is the worst shortage of Mo-99 that has occurred in the entire history of nuclear medicine,” said Dr. Michael M. Graham, president of the Society of Nuclear Medicine and director of the nuclear medicine division at the University of Iowa in Iowa City. He noted that the field of nuclear medicine emerged in the 1960s and was formally recognized as a medical specialty in 1971.
Impact of the shutdowns
Molybdenum-99 decays into technetium-99m (Tc-99m). The “m” after the 99 denotes that the compound is “metastable,” which means that it does not transform into another element upon its decay.
About 70,000 procedures using Tc-99m are performed worldwide each day, with more than half of those taking place in the US. The radioisotope is used in single-photon emission computed tomography and other gamma camera imaging techniques used to diagnose and evaluate treatment responses for the most serious afflictions, including cancer and heart and brain diseases. These methods can pinpoint the location of disease as well as show biological activity, which not all medical imaging techniques can do.
This shortage of Tc-99m will affect not only patients but also radiopharmacists. In the US alone, about 500 pharmacies sell radiopharmaceuticals and employ more than 1500 pharmacists and 10,000 support staff.
Clinics in Canada already have been hit by monthly bills up to $30,000 higher than before the Chalk River shutdown, according to an article in the Toronto Star Aug. 12, 2009. The national government health care system, Health Canada, has no plans to cover the cost.
Problems and solutions
Molybdenum-99 has a half-life of about 66 hours, and Tc-99m a half-life of about six hours, so they cannot be stockpiled.
In some cases, other tests can substitute for the nuclear medicine studies. However, the substitute methods are riskier. For example, thallium-201 can be used in place of Tc-99m for myocardial perfusion imaging; however, according to Graham, the test takes longer, the image quality is not as good, and the patient receives a higher dose of radiation. “Many of our studies, such as the renal, thyroid, parathyroid and gastric emptying, have no reasonable substitute,” Graham said.
“PET scans often give better pictures than technetium-99m,” said Gordon Edwards, president of the Canadian Coalition for Nuclear Responsibility. As for the cost-effectiveness of PET scanning vs. producing Tc-99m, he added, “PET scan machines are expensive, about $2 to $3 million each, but remembering that Ottawa has poured $1.7 billion into Chalk River since 2006, you could buy 500 to 600 PET machines with this amount of money. Even the money wasted on the Maple [multipurpose applied physics lattice experiment] reactors (about $530 million) would buy over 170 PET scan machines.”
Shown is the Petten reactor in the Netherlands. Courtesy of Wikimedia.
Aside from the Chalk River and Petten reactors, the Safari-1 reactor in South Africa, the Osiris reactor in France and the BR2 reactor in Belgium are among the top five producers of Mo-99. All five reactors producing Mo-99 are more than 40 years old; because nuclear plants usually are decommissioned after about 40 to 60 years of use, the Mo-99 shortage may become permanent soon unless reactors are commissioned in their place.
The University of Missouri Research Reactor center, or MURR, in Columbia, could supply Mo-99 if the facility were upgraded. Rep. Edward Markey of Massachusetts has introduced a $163 million bill in Congress to fund the conversion. According to Graham, “There will be multiple delays in moving forward, but it can probably be online in four to five years.”
A collaboration between Babcock & Wilcox Technical Services Group of Lynchburg, Va., and Covidien of Mansfield, Mass., will help when it is up and running. Covidien is experienced with radiopharmaceutical production and regulatory approvals, while Babcock & Wilcox has a patented liquid phase nuclear technology.
Currently, the US does not make any Mo-99 domestically. About 10 years ago, the National Academy of Sciences concluded in a report that no US facility was needed since Canada had two Maple reactors. “This was obviously a huge mistake, since the Maple reactors do not work properly, and Canada has stopped all effort in trying to make them work,” Graham said. “In addition, they were designed to use highly-enriched uranium, which is no longer desirable because of the risk of its use in the construction of nuclear weapons.”
The top five reactors for production of Mo-99 use fission of uranium-235, the same element used in manufacturing the atom and hydrogen nuclear bombs. Highly enriched uranium (HEU) irradiated fuel was returned to the US from Chalk River to make nuclear weapons. “So in this sense, Mo-99 is like a piece of candy that is produced as a by-product of the nuclear weapons business,” Edwards said. “Without nuclear weapons, it would be too expensive to produce the HEU in the first place.” Shipment of HEU to Chalk River is threatened by a US law called the Schumer amendment, which aims to prevent the shipment of nuclear weapons from the US to other countries. But MDS Nordion – a private company that markets the Mo-99 – shows little sign of taking this seriously, Edwards said.
The Petten reactor was shut down for routine maintenance. As for the Chalk River facility, its National Research Universal (NRU) reactor was shut down because heavy water was leaking from a corroded tank inside the reactor core. Heavy water is water with an excess concentration of deuterium, a stable isotope of hydrogen with a neutron as well as a proton. It is not radioactive but is slightly toxic. Heavy water can contain tritium, which is a radioactive form of hydrogen with two neutrons. According to officials, this leak was contained within the facility and poses no risk to humans or to the environment.
Repairs are made to the NRU reactor at Chalk River. Courtesy of AECL.
The tank is about 3.5 m (12 ft) in height and about the same in diameter. Repairing the tank will require lowering tools from small openings in the top of the reactor down 30 to 40 ft to the sites of the corrosion at the bottom of the reactor. The tools must be lowered remotely because of strong radiation fields. In 2007, the reactor was shut down because power was not supplied to two pumps used to prevent a nuclear meltdown. The Chalk River facility is on the banks of the Ottawa River, which flows into the city of Ottawa, the capital of Canada. The city is only 180 km southeast of the reactor.
Early in the summer of 2009, Hugh MacDiarmid, president and CEO of Atomic Energy of Canada Limited, which runs the reactor, said that “we will never operate an unsafe reactor” and that he believed that the NRU would return to service within three months. A few weeks later he told CTV.ca that the three-month figure was “optimistic.”