Imaging Tests for Colorectal Cancer

When you need them—and when you don’t

CT scans and PET-CT scans are two types of imaging tests. They take pictures of the inside of your body. They can give doctors important information about your health.

If you have colorectal cancer, you are likely to have some imaging tests.

  • Shortly after you learn that you have colorectal cancer, imaging tests are often done. These can help your doctor find the cancer and learn if it has spread. This is called staging. It helps your doctor choose treatments that could help you.
  • When your treatments are done, you are likely to have imaging tests again from time to time. This is to make sure the cancer has not come back.

There are reasons to limit imaging tests. They use radiation, they may be costly, and they may not change how you are treated. Your doctor should only order tests if they are needed.

A CT scan can help with staging and follow-up.

The best test for staging and follow-up of colorectal cancer is a CT scan of the chest, abdomen, and pelvis. A CT scan is an X-ray that uses a special kind of dye. It highlights parts of your body that the doctor needs to see. This test is sometimes called a contrast-enhanced CT. It usually gives your healthcare team all the information they need.

PET-CT scans are usually not needed if colorectal cancer has not spread.

Some doctors also request a PET-CT scan. This test uses a substance called a tracer that makes cancer cells visible. The tracer gives off radiation.

Studies have not found that routine PET-CT scans provide any more information than a contrast-enhanced CT scan. If your colorectal cancer has not spread, a PET-CT scan is usually not helpful.

PET-CT scans have risks.

  • They give off more radiation than CT scans, due to the tracer. One test is not harmful, but radiation builds up if you are exposed many times. This can increase the risk of other cancers in the future.
  • PET-CT scans can cost about three times more than CT scans, even though they often don’t provide any extra information.
  • PET-CT scans can sometimes lead to false alarms, because they can find things that aren’t really a problem. That can lead to more tests and costs.

Here are some times when a PET-CT scan may be helpful.

  • Your doctor finds something suspicious on a contrast-enhanced CT scan.
  • Blood tests or a physical exam show that the cancer may have spread or come back.
  • You are allergic to the contrast material used in CT scans.
  • You have certain kidney problems.

A PET-CT scan is more likely to be useful if you have advanced cancer.

This report is for you to use when talking with your healthcare provider. It is not a substitute for medical advice and treatment. Use of this report is at your own risk.

© 2017 Consumer Reports. Developed in cooperation with the Society of Surgical Oncology.