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PET Scan Use in Cancer Diagnosis and Treatment Monitoring

Finding cancer at its earliest stage can give the best chance of being able to cure it. Different tests are used to find cancer and to help find out if the cancer has spread. A positron-emission tomography (PET) scan is one type of test that can help find and stage cancers, as well as monitor how well treatment is working.

PET scans may be used to find, stage, and monitor these different cancers, among others.

  • Breast

  • Colorectal

  • Head and neck

  • Lymphoma

  • Lung

  • Melanoma

  • Ovarian

PET scans are also used for certain noncancerous brain and heart disorders.

What Is PET?

Most common medical imaging tests, like CT and MRI scans, show details about the structure of your body. PET scans are different. They also provide information about function. PET scans may be able to show these changes before structural changes become obvious. With a single PET scan, doctors can collect images of function throughout the body, uncovering abnormalities that might otherwise go undetected.

Cancer Can't Hide From PET

Normal body cells grow, divide, and die in an orderly fashion, replacing worn-out or dying cells and repairing injuries. Sometimes normal cells begin to grow uncontrollably. These abnormal cells continue to grow and divide, forming new abnormal cells. The mass of extra cells forms a growth or tumor. The tumor can be noncancerous, called benign. Or the tumor can be cancerous, called malignant. Benign tumors can be removed with little chance that they will come back. Benign tumors are usually not life-threatening.

If the tumor is cancer, cells can break off from it and travel through the bloodstream or lymphatic system to other parts of the body, where they grow and replace normal tissue. This process of the cancer spreading is called metastasis. Cells from a malignant breast tumor can spread to other tissues, such as the bones. Although these cells are in the bone, the cancer is still called breast cancer.

  • A number of studies have shown that PET scans can help diagnose both benign and cancerous tumors. This may be helpful in telling which people need surgery and which people can avoid it. For example, traditionally, a person who has an abnormal mass in his or her lung would have a biopsy to find out if it was cancer or benign. A PET scan may show that it is unlikely to be cancer, and therefore it may be possible to avoid the biopsy.

  • PET scans can also show the extent of disease--called the stage--of lung cancer, colorectal cancer, melanoma, head and neck cancer, breast cancer, lymphoma, and many other cancers. For people whose cancer has been just recently diagnosed, it is important to know the cancer's stage, which is based on how large the cancer is and if and where it has spread in the body. Staging the cancer helps doctors find the most appropriate treatment. PET scans can search the body for cancer in a single examination, called a "whole body scan," which may show if the cancer has spread and, if so, where.

  • PET scans can monitor how well treatments are working or see if the cancer has come back. For example, one woman with a history of ovarian cancer had an annual blood test that showed a rise in her tumor marker levels. This could have meant that the cancer had come back. Her CT and MRI scans were normal. She then had a PET scan, which showed that her cancer had come back in her liver. After treatment, another PET scan showed that the cancer was gone.

What Happens During a PET Scan?

PET images are different from more conventional imaging tests, such as X-ray, CT, ultrasound, and MRI. These images show what the tissues look like. PET images contain information about how tissues are functioning.

In cancer, cells begin to grow at a much faster rate, using more sugars like glucose than normal tissues. PET works by using a small amount of a radioactive tracer attached to glucose or other compounds. The scanner looks to see which areas are using more glucose--a sign of possible cancer.

If you're getting a PET scan, typically, you'll be told not to eat or drink anything after midnight the night before your scan. You can have a PET scan as an outpatient.

The day of your scan, you are injected with a small amount of radioactive glucose (or similar tracer). It travels through your body and eventually collects in the organs or tissues that are using the glucose. There is very little danger to you from this injection.

After the injection, you will wait approximately an hour while the tracer flows throughout your body. Then, you'll lie on a table that passes slowly through the scanner. The scanner resembles a CT scanner, but has a much larger opening.

If the tissue or an area in an organ is cancerous, the signals will be stronger than in the surrounding tissue. Stronger signals show that more glucose was used. A scanner records these signals and transforms them into color pictures of chemistry and function.

You can expect to be in the PET center for 1-1/2 to 3 hours, but the actual scan does not take this long. The radiation exposure associated with PET is similar to a conventional CT scan. You should feel fine after the scan. There are usually no side effects from the injected tracer.

The results are read shortly after the PET scan is completed, and you can expect your doctor to be told what was seen during the scan the same day.

Will My Insurance Cover a PET Scan?

Most insurance companies pay for clinically indicated PET procedures. Your insurance company may require pre-authorization before the scan. Doctors routinely provide clinical information to the insurance company to get their approval. It is important to contact your insurance company to see if the PET scan is covered.