What is a PET Scan for Cancer? A Comprehensive Guide

Positron Emission Tomography, most commonly known as a PET scan, is an advanced imaging technique that provides detailed, three-dimensional (3D) pictures of the inside of your body. As a vital tool in modern medicine, particularly in oncology, PET scans utilize a mildly radioactive substance, called a radioactive tracer, to highlight areas of cellular activity. This capability is crucial for diagnosing various medical conditions, most notably cancer, and understanding its behavior within the body.

Often performed in the radiology or nuclear medicine departments of hospitals, typically on an outpatient basis, PET scans are frequently found in major cancer centers. This might mean that patients need to travel to specialized facilities to undergo this procedure. A trained radiographer operates the PET scanner, and the entire process, from preparation to scan completion, usually takes around 45 to 60 minutes for the scan itself, with an additional hour needed beforehand for tracer administration.

To enhance diagnostic accuracy, PET scans are frequently combined with other imaging modalities. When integrated with a CT (Computed Tomography) scan, it becomes a PET-CT scan, offering a more detailed anatomical and functional view. Similarly, combining PET with MRI (Magnetic Resonance Imaging) results in a PET-MRI scan, further enriching the information obtained.

Why is a PET Scan Necessary for Cancer?

PET scans play a pivotal role in cancer management, offering valuable insights at various stages of the disease. Here are key reasons why a doctor might recommend a PET scan:

Cancer Detection: PET scans are highly effective in detecting cancerous tissues within the body. Cancer cells exhibit higher metabolic activity compared to normal cells, causing them to absorb more of the radioactive tracer. This increased uptake makes cancerous areas “light up” on the scan, aiding in early detection.
Staging Cancer: Understanding the extent of cancer spread is critical for effective treatment planning. PET scans help determine the size of a tumor and whether it has metastasized, or spread, to other parts of the body. This process, known as staging, is crucial for determining the severity of the cancer and guiding treatment strategies.
Distinguishing Cancer from Benign Lumps: Not all lumps are cancerous. A PET scan can help differentiate between malignant (cancerous) and benign (non-cancerous) masses. If a lump shows high metabolic activity on a PET scan, it is more likely to be cancerous.
Guiding Treatment Decisions: The information from a PET scan assists doctors in selecting the most appropriate treatment approach for each individual. By providing a clear picture of the cancer’s location and extent, PET scans ensure that treatment plans are precisely tailored to the patient’s specific needs.
Monitoring Treatment Effectiveness: PET scans are valuable for evaluating how well cancer treatment is working. By comparing scans taken before, during, and after treatment, doctors can assess whether the cancer is responding positively to therapy, such as chemotherapy or radiation.

Furthermore, after cancer treatment, other imaging tests like CT scans might still show residual abnormalities. However, these could be due to inactive scar tissue rather than active cancer cells. A PET scan can distinguish between these scenarios, helping to determine if there is still active cancer present or if the abnormalities are simply remnants of previous treatment.

In certain cancers, PET scans are also specifically used to examine lymph nodes in the central chest area, helping to identify potential spread in these critical locations.

Preparing for Your PET Scan

Proper preparation is essential for ensuring the accuracy and effectiveness of a PET scan. Here are the standard preparation guidelines:

Fasting: For most PET scans, it is necessary to abstain from eating for approximately 4 to 6 hours before the procedure. However, drinking plain water is usually permitted during this fasting period.
Exercise Restrictions: You might receive instructions to avoid strenuous physical activity for 12 to 24 hours prior to your scan. Exercise can affect the distribution of the radioactive tracer in your body, potentially impacting the scan’s results.
Diabetes Considerations: If fasting poses a problem due to diabetes or other medical conditions, it is crucial to contact the number provided on your appointment letter. Adjustments to your diet, sugar control, or appointment time might be necessary to accommodate your needs.
Claustrophobia Concerns: If you are prone to claustrophobia or anxiety in enclosed spaces, inform the department staff beforehand. They can take extra measures to ensure your comfort, explain the procedure in detail, and, if needed, your doctor can prescribe medication to help you relax during the scan.

What to Expect During a PET Scan

Understanding the steps involved in a PET scan can help alleviate anxiety and prepare you for the procedure.

At the Hospital

Upon arrival at the hospital, a radiographer will guide you through the initial steps:

Changing into a Gown: You may be asked to change into a hospital gown to ensure no metal interferes with the scan.
Metal Object Removal: All jewelry and metallic items, including hair clips, coins, belts, and wired bras, must be removed. Metal can distort the PET scan images, reducing their diagnostic quality.
Tracer Injection: Approximately an hour before the scan begins, you will receive an injection of the radioactive tracer. This is administered through a small plastic tube, called a cannula, inserted into a vein in your arm. The amount of radiation is minimal and considered safe.
Rest Period: After the injection, you will need to rest quietly for about an hour, minimizing movement. This waiting period allows the radioactive tracer to circulate throughout your body and be absorbed by your tissues.
Radioactive Tracer Explained: The tracer is typically a radioactive form of glucose, most commonly fluorodeoxyglucose (FDG). Cancer cells, due to their rapid growth and high metabolic rate, require more energy than normal cells. Consequently, they absorb more of the FDG tracer, causing them to appear brighter on the PET scan images.

In the Scanning Room

Once the tracer has had sufficient time to distribute, the radiographer will escort you to the scanning room:

The PET Scanner: The PET machine is a large, doughnut-shaped device.
Positioning: For most scans, you will lie down on your back on a movable couch that slides into the scanner.
Radiographer Communication: Once you are positioned correctly, the radiographer will move to the control room, but they will be able to see you at all times via a TV screen or window and you can communicate with them through an intercom system.

Undergoing the PET Scan

During the scan itself:

Couch Movement: The couch will slowly move in and out of the PET scanner. As you move through the scanner, it will take images of your body.
Painless Procedure: The scan is painless, but it is crucial to remain still throughout the process to ensure clear images. If you experience discomfort or need to move, inform the radiographer.
Noise Level: The scanner is not excessively noisy, but you will hear a continuous background hum. In many facilities, music can be played to help you relax during the scan.
Scan Duration: The actual scanning process typically lasts between 45 and 60 minutes.
Completion: Once the scan is complete, the radiographer will return to the room, lower the couch, and assist you in getting up.

After Your PET Scan

Following the PET scan, the cannula will be removed from your arm before you leave the hospital. Post-scan instructions are generally straightforward:

Resume Normal Activities: You can eat and drink as usual immediately after the scan.
Hydration: Drinking plenty of fluids helps to flush the radioactive tracer out of your body more quickly.
Radiation Precautions: While the radiation dose from the tracer is very low and diminishes rapidly, as a precaution, it is advised to limit close contact with pregnant women, babies, and young children for about 6 hours after the scan.
Sedation Aftereffects: If you received medication to help you relax, you will need someone to drive you home and stay with you overnight. For the next 24 hours, it is also advised to avoid driving, consuming alcohol, operating heavy machinery, and signing legal documents, as your judgment and reflexes may be impaired.
Airport Travel: If you are traveling internationally within a week of your PET scan, carrying your appointment letter is advisable. Airport security systems often have sensitive radiation detectors that might pick up trace amounts of radiation from the tracer still in your body.

Potential Risks Associated with PET Scans

PET scans are generally considered safe for most individuals. However, like all medical procedures, there are some potential risks to be aware of:

Pregnancy: PET scans are typically avoided during pregnancy unless absolutely necessary in an emergency situation, as there is a theoretical risk of radiation exposure to the developing fetus. If you are pregnant or suspect you might be, inform the medical staff beforehand.
Breastfeeding: If you are breastfeeding, notify the department a few days prior to your appointment. They will provide guidance on whether you need to temporarily discontinue breastfeeding after receiving the radioactive tracer. You may need to store expressed breast milk in advance for at least one feeding.
Radiation Exposure: The radiation from the tracer slightly elevates the long-term risk of developing cancer. However, this risk is considered very small and is outweighed by the diagnostic benefits of the PET scan, especially in cancer management. If you have concerns about radiation exposure, discuss them with your doctor.
Bruising and Swelling: A minor bruise may occur at the injection site. In rare instances, the tracer may leak out of the vein, causing temporary swelling and discomfort in the arm.
Allergic Reactions: Allergic reactions to the radioactive tracer are rare, but possible. Symptoms may include weakness, sweating, and breathing difficulties. If you feel unwell at any point during or after the scan, immediately inform the radiographer.

Receiving Your PET Scan Results

After your PET scan, a specialist doctor will analyze the images. You can expect to receive your results within 1 to 2 weeks. It’s important to note that results are not provided at the time of the scan itself.

Waiting for medical test results can be an anxious time. Ask your doctor or nurse for an estimated timeframe for when you can expect your results and don’t hesitate to contact them if you haven’t heard back within that period.

You may also have access to a specialist nurse who can provide information and support during this waiting period. Talking to friends or family about your feelings can also be helpful. For additional support and information, resources like cancer support helplines are available.

This comprehensive guide aims to provide a clear understanding of what a PET scan for cancer is, its importance, and what to expect before, during, and after the procedure. It is designed to empower patients with knowledge and alleviate any anxieties associated with this valuable diagnostic tool.