What is Nuclear Medicine?

Radiation therapy machine. Source: Canadian Nuclear Association.

Radiation as a medical tool

Cancer is responsible for a quarter of deaths in Canada, and it is a tough battle. Doctors must locate a cancerous tumour precisely, then get to it without damaging healthy tissues nearby.

Certain radioactive materials, called medical isotopes, help doctors to find and treat cancer. Produced in nuclear reactors, these are radioactive versions of naturally occurring atoms. This radiation can pass right through body tissue, helping doctors to see cancer cells and treat them.

Canada is a world leader in producing medical isotopes. It has been responsible for advances in nuclear medicine that have helped millions of people around the world to live better and longer lives.

Nuclear imaging

Scan showing cancer that has metastasized. Source: About Cancer.

Radiation from medical isotopes can be detected and imaged. By selecting the right medical isotope and injecting it into the body, doctors can make several types of useful “pictures” of your body’s organs, bones, tissues, and other structures.

Some isotopes enter body organs quickly. A medical technician can inject an isotope into your body, wait for it to move to the organ, and then take a two- or three-dimensional picture of the organ – without using a scalpel. For example, because the thyroid gland absorbs iodine quickly, an isotope called iodine-123 makes clear images of it.

Another technique uses sugar, which cancer cells consume faster than healthy cells. Using sugar treated with the isotope fluorine-18, a medical technician can take a highly accurate picture of a tumour, enabling treatment.

Nuclear imaging can also be used to assess bone growth, find where blood flow is clogged, and produce time-lapse images of organs.

Radiation therapy

It is possible to focus radiation on a tumour while limiting the risk to nearby healthy tissue. That is the core technique of radiation therapy, which works because cancer cells are more vulnerable to radiation than healthy cells are.

There are three main ways to do this:

  • Injections of an isotope can focus radiation on a specific organ.
  • Implantation involves placing radioactive sources directly in the cancerous tissue.
  • External beam-radiation therapy focuses beams of radiation onto the tumour from many angles. One of the most important beam-radiation methods uses the isotope cobalt-60. Canadians Harold E. Johns and Roy Errington pioneered this method in 1951 in London, Ontario.

Is nuclear medicine safe?

Though radiation can save lives, it is also very important to limit radiation exposure to any healthy tissue. Medical technicians do this by focusing radiation on a tumour. They use medical isotopes that leave the body or become less radioactive quickly. For example, less than 1% of fluorine-18 (FDG) remains in your body after 12 hours.


Most nuclear procedures use radiation doses similar to what you experience from natural background radiation, which comes from sources such as the sun. These doses are well within radiation safety limits. And, with 1.5 million diagnostic images and 15,000 therapeutic doses each year in Canada, these procedures save many lives.


Canadian Nuclear Association, https://cna.ca/.