PET Scans for Lymphoma

PET stands for positron emission tomography, and it is considered a type of "nuclear medicine" imaging. Nuclear imaging tests all have in common the use of a small amount of radioactive material in order to image the body or some aspect of it's function, such as blood flow, metabolism, oxygen use or glucose uptake.

X-rays, CT scans and MR scans are used to image your body to reveal structures that differ in their physical characteristics, including to identify tumors based on their size, shape and location. PET scans differ depending on the type used, but a common one uses a radioactive sugar to identify cancers based on the uptake of that sugar by cancer cells.

What Do PET Scans Offer?

CT scans and MR scans can obtain excellent images of different parts of the body, and identify enlarged nodes or tumor masses. However, sometimes it is difficult to tell whether a lump or mass in the body actually has tumor cells in it only by measuring its size and shape. Small lumps or nodes may contain cancer cells, while larger ones may just be something harmless. PET scans can help identify cancerous cells that are found within normal-appearing structures. They can also help identify cancer in areas not previously thought to be involved by the spread of the disease. All of this detecting ability does have a down side—that is, the potential for false positive findings. However, awareness of uptake patterns and limitations of PET helps to guide the doctors who interpret these studies.

Using PET Scans for Lymphoma

PET scans have many uses in lymphoma:

  • They can be used for staging, or mapping the disease in your body, along with other tests like CT scans.
  • The PET scan report can help decide what kind of treatment is best for you, such as chemotherapy or radiation.
  • It can show whether a lump on a CT scan has cancer or not.
  • It can help in assessing how well you are responding to treatment, when done after a few cycles of chemotherapy.
  • After treatment is over, PET scans can determine whether an area of concern has active cancer cells or just scar tissue.

How Are PET Scans Done?

There is generally a period of several hours during which patients cannot eat anything prior to the scan time. Specifics of the procedure depend on the type of PET scan being performed. If the radiotracer is given intravenously, a small amount of radioactive material is injected prior to performing the scan. The whole process from beginning to end can take a couple of hours. You can listen to music on a CD player to help you relax. When the scan is over, you can leave within a short period of time.

What Is FDG-PET?

FDG is Fluoro-deoxy glucose, a special form of radioactive glucose that is used for PET scans. Tumor tissue uses glucose faster and in a different way that normal tissues. FDG accumulates within tumor cells. That is how a PET scan is able to tell the difference between normal and tumor cells.

Are PET Scans Essential?

For some types of lymphoma, and for certain clinical scenarios, PET scans are becoming viewed more and more as essential. The standard form of imaging test in lymphomas is the CT scan. Modern CT scanners have excellent resolution and they can pick up the smallest lymph-nodes. PET scans are used mainly as an additional test because of some of the advantages of this imaging method. Not all patients need to have PET scans, but they can be very useful in some situations, such as when CT scans leave unanswered questions.

PET Scan Frequency During Follow-Up

There are no absolute rules for the frequency of PET scans, although experts are trying to come to consensus for a few specific clinical scenarios. PET scans need not be done repeatedly as a follow-up test. Most hospitals use CT scans for routine follow-up, and use PET scans when they need some extra help. You should speak to your doctor regarding your hospital policy.

Side Effects of PET Scans

The amount of radioactivity in the injection is low, but PET scans are often combined with CT scans which deliver a higher dose of radiation. Although there are risks from PET scans and from exposure to radiation, risks and benefits should be weighed carefully in all instances. If you are having a PET/CT scan, it is likely that the benefits of such a study greatly outweighed the risks in the estimation of the treating physician, but you should always be clear on the risks and benefits as they apply to you, and ask any question you may have.

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