A positron emission tomography (PET) scan is an imaging technique that uses small amounts of radioactive substances. Doctors may use PET scans in chemotherapy treatments for cancer.

PET scans help doctors to determine whether the organs and tissues of the body are working properly. The procedure can identify any changes in blood flow, metabolism, and the chemical composition of certain parts of the body.

This article discusses the role of PET scans in chemotherapy, how they work, what to expect, and more.

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Chemotherapy is a cancer treatment that uses medication or drugs to treat or manage cancer. Doctors recommend the drug or combination of drugs depending on the type of cancer and its stage.

A person may require a PET scan before chemotherapy to determine how far and to where the cancer has spread.

A PET scan is an imaging technique that uses radiotracers containing small amounts of radioactive substances attached to natural chemicals. They mostly include fluorine-18 (18F) fluoro-deoxyglucose (FDG), which cells take up instead of regular glucose for metabolism.

Cancer cells are metabolically more active than other cells, so they take up FDG in place of glucose at a higher rate. This causes them to build up at the location of cancer, where they appear as bright spots on the PET scan.

PET scans are also used after chemotherapy to determine whether the treatment was effective. It can help identify whether there is any sign of cancer following treatment. PET scans after chemotherapy can also check for whether the cancer has come back.

A person will typically receive a PET scan a number of weeks after the end of the chemotherapy treatment to ensure the most accurate results.

Learn more about chemotherapy.

PET scan works by detecting radiation emitted by a radiotracer. Radiotracers are made of radioactive material tagged to a naturally occurring chemical, such as glucose. FDG is the most commonly used radiotracer.

Administration of the radiotracer takes place either orally, intravenously, or through inhalation. It takes some time to spread throughout the body. During this process, it gets trapped in different tissues of the body that take up glucose.

A special camera then detects gamma rays from the radiotracer. The camera uses this data to produce images and provide molecular information.

The time taken for the entire procedure ranges from 30 minutes to 1 hour.

Learn more about PET scans.

Doctors generally provide instructions on how to prepare for a PET scan. It is important for a person undergoing PET scans to inform their doctors about the medications they are taking, including herbal and vitamin supplements, as well as if they have any allergies or medical conditions.

A few of the general instructions before undergoing a PET scan include the following:

  • Avoid strenuous physical activity 24 hours before the scan.
  • Avoid eating or drinking anything other than water 6 hours before the scan.
  • Remove metal objects such as jewelry, hairpins, and eyeglasses.
  • Remove removable dental work and hearing aids.

People with diabetes may receive special instructions on how to prepare for the exam. Additionally, anybody who is nursing a baby should get their doctor’s advice on how to proceed. The doctor may advise pumping breast milk before the scan for use until the radiotracer is no longer in the body.

PET scans happen on an outpatient basis. This means people do not have to stay at the hospital overnight.

Administration of the radiotracer takes place by injecting it into a vein of the arm, drinking a solution, or inhalation. People need to wait for about 1 hour after administration of radiotracer since it takes time to spread throughout the body.

During this time, people need to relax and avoid moving or talking because this can affect the spread of the radiotracer. They may be seated in a comfortable chair with comfortable blankets.

The scan itself involves lying on a flat bed that moves into a large cylindrical scanner. The position of the individual may depend on which area of the body is being examined. Scanning takes about 30–60 minutes.

People need to remain still during scanning and might also need to hold their breath for a brief period. The technologist carrying out the procedure generally lets people know once the scanning is complete and also if more images are essential.

In certain cases, people undergo additional tests using other tracers or drugs. This could take additional time up to 3 hours.

Most often people do not experience any side effects following a PET scan.

Those who receive the radiotracer intravenously may feel a pin prick at the area where the insertion of the needle takes place and a cold sensation moving up the arm during the injection.

Most people can resume their daily activities after the procedure. In some cases, doctors recommend special instructions to people before they leave.

People undergoing PET may need to drink plenty of water and fluids to flush the radiotracer out of the body.

Since PET scans use a radiotracer, there can be a risk of radiation exposure. The amount of radiation exposure is low and, in most cases, the benefits of the procedure outweigh the radiation risk.

People should still discuss any possible risks with their doctors before undergoing the procedure. Doctors may advise them to avoid close contact with pregnant people, infants, and young children just after the procedure to avoid any radiation risks.

In very few cases, PET scans can lead to potential tissue damage that could develop into cancer at later stages.

Here are some more frequently asked questions about PET scans and chemotherapy.

Why does a person need a PET scan before chemotherapy?

PET scan before chemotherapy is important for detecting the location and the stage of the cancer. This in turn helps doctors to determine which chemotherapy option and dose will be most suitable for a particular person.

Why does a person need a PET scan after chemotherapy?

People may need a PET scan after chemotherapy to detect whether there are some signs of cancer left following the treatment, whether the treatment was effective, and if there is a recurrence of cancer.

Can a PET scan be done during chemotherapy?

PET scans take place before or after chemotherapy. They usually do not take place while the chemotherapy is still going on because the scan readings may not accurately show how well the treatment is working until a few weeks after the end of the treatment.

How often does a person get PET scans during chemotherapy?

People most likely get PET scans every 6–8 weeks, or every two cycles of chemotherapy. However, this might differ as per the type of cancer and its severity.

PET scans are imaging techniques that help to determine whether the tissues and organs of the body are working properly. They use radiotracers containing radioactive substances to assess conditions faster than other imaging tests.

Administration of the radiotracers in PET scans takes place intravenously, orally, or by inhaling. These then distribute across the body and get absorbed in areas of high affinity. Cancer cells, which are more metabolically active, absorb them at a higher rate.

PET scans can help to determine the location and stage of cancer as well as the effectiveness of chemotherapy. It is best for a person to discuss with their doctor how to prepare for a PET scan, what they can expect afterward, and any risks they need to consider.