Positron emission tomography (PET) scans are common tools that oncologists use to diagnose lung cancer, assess its stage, or evaluate how well your treatment is working. You may be asked to have a PET scan while you’re first getting diagnosed or periodically during or after lung cancer treatment to monitor whether the disease is progressing.

Before you go in for your PET scan, it can help to understand everything you can about the procedure. That way, you’ll be prepared for what will happen, and you’ll know what your doctor is looking for in the results.

Read on to find out how PET scans work, when they’re used in lung cancer, and why they’re considered accurate and reliable.

How Does a PET Scan Work?

A PET scan produces 3D pictures of your whole body. PET scans are relatively noninvasive. First, a tracer drug made of slightly radioactive glucose (sugar) is injected into your body. The drug shows doctors where the cells in your body have increased activity. These areas can indicate the presence of cancer and other health conditions.

What Does Lung Cancer Look Like on a PET Scan?

Cancer cells usually grow quickly, and they need sugar to fuel this growth. Cancerous cells tend to absorb the radioactive sugar quickly, and this activity shows up as white or lighter spots on a PET scan.

Your doctor may order a PET scan or a combination PET-computed tomography (PET-CT) scan. The combination of PET and CT scans gives doctors even more information to work with when diagnosing a condition like lung cancer.

Diagnostic Accuracy of PET Scans in Lung Cancer

PET and combined PET-CT scans are the most accurate tools available for determining where cancer cells are in your body before, during, and after treatment. These scans can sometimes provide a noninvasive option to determine if cancer is in the lymph nodes, and they can usually tell whether lung nodules are cancerous or benign.

False-Positive Results

Occasionally, inflammation caused by diseases other than cancer may light up on PET scans. This is why there’s a small false-positive rate of 6.5 percent, according to one large study. This means that about 6.5 percent of the time, PET scans can show abnormalities that make it look like you could have lung cancer when you don’t.

False-Negative Results

On the other hand, if someone has a single mass — known as a solitary pulmonary nodule — smaller than 1 centimeter, it may be hard to determine if it’s lung cancer. This puts some people at risk for a false-negative test result. In other words, a scan may indicate that you don’t have a lung tumor when you do.

Whenever a lung cancer diagnosis is unclear, other tests such as a biopsy can confirm cancer or rule it out. A biopsy involves removing a tissue sample for examination under a microscope.

Overall, however, PET is the most accurate form of lung cancer imaging available, especially when combined with other testing methods in uncertain situations.

When Do Doctors Order Lung PET Scans?

Doctors may use PET scans at several points during lung cancer diagnosis and treatment. They’re also used to check whether lung cancer has returned.

Diagnosing Lung Cancer

The PET scan allows your doctors to see whether you have tumors growing on, in, or around your lungs. Scans can also show whether a particular lump or spot on your lungs may be cancerous or related to other health conditions.

To diagnose lung cancer, PET scans are often used alongside other tests including:

• Blood tests
• Bronchoscopy
• Chest X-rays
• X-rays
• CT imaging
• MRI imaging

Staging Lung Cancer

PET scans can show doctors:

• How big tumors are
• How many tumors there are
• Where exactly tumors are located
• Whether cancer has spread (known as metastasis) into nearby lymph nodes or other body parts

All of this information helps your doctors determine what stage of lung cancer you have.

Recommending a Lung Cancer Treatment Plan

PET images can show oncologists where they should take a biopsy to test for lung cancer. The images can also help doctors determine which treatment options would be best, based on factors like the specifics of a person’s tumor or tumors.

Evaluating Treatment Effectiveness

A PET scan can show doctors whether lung cancer is responding to current treatments. It can show tumors getting larger or smaller, spreading, or even disappearing. Using PET scans in this way is controversial, but many doctors believe these images, in addition to other tests, are helpful in evaluating whether a particular treatment is working.

Managing Ongoing Care

PET scans can be used to follow up and determine whether lung cancer has returned. This type of follow-up can help doctors catch returned cancer early so it can be treated effectively. This is a controversial use of PET scans, however, as some doctors believe that the scans aren’t worth their high cost and the exposure to radioactive tracers.

How To Prepare for a Lung PET Scan

Your health care provider should give you specifics for preparing for your PET scan. Make sure to inform your doctor if you:

• Have had serious allergic reactions in the past
• Have recently had an acute illness
• Have diabetes or other chronic medical conditions
• Have any reason to believe that you might be pregnant
• Have had claustrophobia (fear of confined spaces) before, particularly when getting a medical scan
• Have been on any medications, including over-the-counter medications, prescribed medications, or supplements
• Have been breastfeeding

You will likely need to stop eating for at least a few hours before the scan, though some scans require you not to eat for six hours. You may also be asked to avoid exercise for up to 24 hours before the scan.

What To Expect When Getting a Lung PET Scan

The radioactive tracer is usually injected intravenously (into a vein with an IV). Your technician will give you specific instructions so you know what you need to do. Once you have received the tracer, you will be asked to wait in the radiology or nuclear medicine department while your body absorbs it.

About an hour after the tracer drug is injected, you’ll be asked to lie down on a platform in the PET scanner machine. A PET scanner looks like a large metal bagel. The platform will slide slowly back and forth through the machine. It’s painless to receive a PET scan, but you’ll need to hold very still. The scan itself takes about an hour.

If you feel anxious during the scan, you can let the technician know. If you know beforehand that you might feel anxious, you can ask for medication that will help you relax.

How Long Does It Take To Get PET Scan Results?

You should receive results from your PET imaging scan within a few days. This waiting period can cause anxiety for many people. “Trying to stay busy,” one MyLungCancerTeam shared. “I get my PET scan results and my brain MRI results both on Friday. The waiting is hard.”

Remember that your doctor only wants the best for you, and it’s always better to have more information about your condition so you can make informed choices about treatment. Before long, you should know what your PET scan showed.

Your oncology team will use your PET results to help accurately determine your lung cancer diagnosis, stage, treatment plan. If results are unclear, your treatment team may recommend additional testing that must be done to determine the best next steps in your care. Remember, you can always ask for a second opinion on your scan results and next steps.

Get Support From Others Who Understand

On MyLungCancerTeam, the social network for people with lung cancer and their loved ones, more than 121,000 people from around the world come together to ask questions, offer support and advice, and connect with others who understand life with lung cancer.

Have you had one or more PET scans for lung cancer? Do you have tips for others undergoing this test? Share your experience in the comments below or by posting on MyLungCancerTeam.