Nuclear medicine scans can help doctors find tumors and see how much the cancer has spread in the body (called the cancer’s stage). They may also be used to decide if treatment is working. These tests are painless and usually done as an outpatient procedure. The specific type of nuclear scan you’ll have depends on which organ the doctor wants to look into. Some of the nuclear medicine scans most commonly used for cancer (described in more detail further on) are:
- Bone scans
- PET (positron emission tomography) scans
- Thyroid scans
- MUGA (multigated acquisition) scans
- Gallium scans
How do they work?
In most cases you’re given a tracer (or radionuclide) that sends out small doses of radiation. Some are swallowed while others are put into a vein or inhaled as a gas.
Over time the tracer collects in the part of the body that’s being tested. This can take from a few seconds to several days. The collected tracer sends out gamma rays that are picked up by a special camera (a gamma camera, rectilinear scanner, or scintiscan). The signals are processed by a computer, which turns them into 2- or 3-dimensional (3-D) pictures, sometimes with color added for extra clarity. A radiologist or a doctor who specializes in nuclear medicine interprets the pictures and sends a report to your doctor.
These nuclear medicine scans are commonly used for cancer:
Bone scans: Bone scans look for cancers that may have spread (metastasized) from other places to the bones. They can often find bone changes much earlier than regular x-rays. The tracer collects in the bone over a few hours, then the scans are done.
Positron emission tomography (PET) scans: PET scans usually use a form of radioactive sugar. Body cells take in different amounts of the sugar, depending on how fast they are growing. Cancer cells, which grow quickly, are more likely to take up larger amounts of the sugar than normal cells. You’ll be asked to not drink any sugary liquids for several hours before the test.
PET/CT scans: Doctors often use machines that combine a PET scan with a CT scan. PET/CT scanners give information on any areas of increased cell activity (from the PET), as well as show more detail in these areas (from the CT). This helps doctors pinpoint tumors. But they also expose the patient to more radiation.
Thyroid scans: Radioactive iodine (iodine-123 or iodine-131) is swallowed. It goes onto the blood stream and collects in the thyroid gland. This scan can be used to find thyroid cancers. Radioactive iodine can also be used to treat thyroid cancer. This test may not work the way it should if you take in substances that contain iodine contain iodine (such as seaweed, cough syrups, multivitamins, or certain heart medicines). Be sure you tell your doctor about any allergies to seafood or iodine. Talk to the doctor about what you need to do to be ready for this test.
MUGA scans: This scan looks at heart function. It may be used to check heart function before, during, and after certain type of chemotherapy. The scanner shows how your heart moves your blood as it carries the tracer, which binds to red blood cells. The test tells you your ejection fraction, which is the amount of blood pumped out of your heart. 50% or higher is normal. If you have an abnormal result, your doctor may switch you to a different kind of chemotherapy. You may be asked to not use tobacco or caffeine for 24 hours before the test.
Gallium scans: Gallium-67 is the tracer used in this test to look for cancer in certain organs. It can also be used for a whole body scan. The scanner looks for places where the gallium has collected in the body. These areas could be infection, inflammation, or cancer.
How do I get ready for the test?
The steps needed to prepare for a nuclear medicine scan depend on the type of test and the tissue that will be studied. Some scans require that you don’t eat or drink for 2 to 12 hours before the test. For others, you may be asked to take a laxative or use an enema. Be sure your doctor or nurse knows everything you take, even over-the-counter drugs, vitamins, and herbs. You may need to avoid some medicines (prescription and over-the-counter) before the test. Your health care team will give you instructions.
Reactions to the radioactive material are very rare. Still, be sure to tell your doctor about any allergies and if you’ve had problems with nuclear medicine scans in the past.
You may get the radioactive material anywhere from a few minutes to many hours before the test. For example, in a bone scan, the tracer is put into a vein in your arm about 2 hours before the test begins. For gallium scans, the tracer is given a few days before the test.