Medical Isotopes - Frequently Asked Questions

Doctors looking at X-rays

1. What is a medical isotope?

A medical isotope is a safe radioactive substance used primarily to diagnose illness. The energy emitted by the isotope when inside a patient is detected by special cameras while the patient is being scanned. These scans essentially light up the organ and show how it is working rather than what it looks like. The branch of medicine and medical imaging that uses these isotopes is known as nuclear medicine.

2. What is a Curie?

A Curie is a measure of radioactivity. Prescribed doses of medical isotopes are measured in Curies (Ci). Prescribed doses vary depending on the isotope and the area of the body scanned.

3. Why is this issue a concern to Canadians?

Medical isotopes are used primarily to diagnose health conditions. Technetium-99 (Tc-99m) is the medical isotope used in over 80 percent of all nuclear medicine scans in Canada. The shutdown of the Chalk River reactor affects supply. Tc-99m is used in tests to diagnose medical conditions of the heart, the circulatory system, and organs. There is no one alternative for all the uses of Tc-99m, but there are alternatives available for some uses. It is up to the health care provider to make specific decisions about diagnosis and treatment.

4. What is the most common medical isotope?

Tc-99m is the medical isotope used in approximately 80 percent of all nuclear medicine scans in Canada. It is used in tests on the heart, the circulatory system, and organs.

5. What is the process to produce Tc-99m?

The production of Tc-99m begins with the fission of the isotope Uranium-235, which produces radioactive Molybdenum-99. Molybdenum-99 is further processed and refined and shipped to a distributor, who puts the substance into a container, called a generator, for sale and shipment to hospitals and radiopharmacies. The Tc-99m is derived from the Molybdenum-99 generator into a saline solution, which is injected into or inhaled by the patient before a diagnostic scan.

6. What is Canada's regular consumption of medical isotopes?

Tc-99m does the majority of nuclear medicine diagnostic tests, about 24,000 out of 30,000 nuclear medicine diagnostic scans per week. There are about 300 therapeutic doses administered each week in Canada.

7. Where does Canada regularly get its medical isotope supplies? Where are supplies coming from now that Chalk River is down? Can you break this down by percentage?

The world's supply of Molybdenum-99/Technetium-99m is from five large commercial reactors. The majority of Canada's supply is sourced from the NRU reactor at Chalk River (between 80-85% when the NRU is operational). Other sources of supply include the European reactors, as well as the reactor in South Africa. Some of these reactors have ramped up production to help lessen the impact of the NRU shutdown, and this additional production has entered the Canadian supply chain.

We have also recently approved the use of isotopes produced in Australia.

8. Do Canadian hospitals have the technology/equipment needed to use medical isotopes other than Tc-99m? What is this technology?

Availability of technology, medical imaging equipment and isotopes will vary from province to province, and from hospital to hospital. Alternative nuclear medicine cameras, known as Positron Emission Tomography (PET) scanners, are another type of nuclear medicine camera. Availability of these cameras is limited, but are available in large urban centres. Alternative isotopes, such as Thallium, can be used in the same type of camera as Tc-99m, and therefore availability will be the same as for Tc-99m. Availability of other imaging modalities, such as MRI and CT, will also vary across the country.

9. What is a half-life of an isotope? What does it mean? What is the half-life of Tc-99m?

The medical usefulness of isotopes dwindles in a predictable way that is measured by the isotope's half-life. The half-life is the time it takes for half the product to lose its radioactivity.

Because most medical isotopes have short half-lives, they can't be stockpiled like other more stable products, such as vaccines. The half-life of Molybdenum-99 (the isotope used to produce Tc-99m) is 66 hours. The half-life of Tc-99m is 6 hours. Generators, containers that encase Molybdenum-99 degrading to Tc-99m, expire after two weeks.

10. What are the alternatives to Tc-99m?

There is no one alternative for all the uses of Tc-99m, but there are alternatives available for some uses. It is up to the health care provider to make specific decisions about diagnosis and treatment. Patient's needs, as well as a facility's ability to access and use alternatives, inform health care providers' decisions about alternatives for diagnosis and treatment. Some alternative isotopes have decay faster than Tc-99m, which makes their availability limited.Footnote 1

Alternative isotopes that can be used with existing cameras:

Alternative isotopes that can be used with existing cameras (SPECT and gamma cameras) offer advantages because they can use existing infrastructure. The alternative isotopes are produced by small accelerators, called cyclotrons, and are not reliant on nuclear reactors.

  • Thallium-201 is approved as an alternative for most heart tests, which account for approximately half of all Tc-99m procedures in Canada.
  • Iodine-123 is approved to image kidneys. It can also be used to image the thyroid gland, and can be made available by request from a physician or through clinical trials.
  • Gallium-67 is approved for detection of Hodgkin's disease and lymphomas, among other types of cancers.

Alternative isotopes that can be used with alternative cameras:

Positron Emission Tomography (PET) scanners are another type of nuclear medicine camera, which use different isotopes from the gamma and SPECT gamma cameras. Availability of these cameras is limited. Alternative isotopes that can be used with these scanners include:

  • 18 F FDG is approved for some cancer scans.
  • 18F Sodium Fluoride can be used for bone-scanning through clinical trials.
  • Nitrogen-13 ammonia can be made available through Health Canada for heart procedures at the request of a physician, or through clinical trial.
  • Rubidium-82 can be made available through Health Canada to replace a small number of heart studies at the request of a physician, or through clinical trial.

There are also alternative scanning technologies such as Magnetic Resonance Imaging (MRI) and Computed Tomography (CT), which can be used for some imaging needs.

11. What are some of the alternatives that Canada's scientific community are currently working on?

The Government of Canada has established an expert panel to review proposals from the private and public sectors for new sources of key medical isotopes for Canada. In order to identify the most promising solutions, the Government of Canada will seek submissions from private and public sector organizations. The expert review panel will assess the concepts and proposals against identified criteria. The expert review panel will bring together world class expertise in the domains of health science, applied science and public policy.

The Canadian Institutes of Health Research (CIHR) has been working closely with others to plan a research strategy. Discussions have focused on the need to: evaluate the state of the science in medical imaging (nuclear and non-nuclear); identify areas where a targeted investment of funds might lead to advances in the field; and address the medical needs created by a potential reduction in access to Molybdenum-99.

As well, the Government of Canada is providing $6 million towards research which will advance research into alternative, non-nuclear, medical isotopes that could replace Technetium-99m in certain medical imaging procedures and support the production and clinical testing of these alternatives.

12. Does Canada have an emergency plan for this type of medical emergency?

Canada has many tools in place to help address the shortage of Molybdenum-99/Technetium-99m. For example, Health Canada shared clinical guidance with the health care community on strategies to maximize the existing supplies of Tc-99m. In addition, there is a regulatory toolkit to help the health care community access alternative isotopes and alternative imaging modalities.

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