Using PET Scans for Evaluating Treatment Response With Lymphoma

PET Scan Use, Timing, and Issues During Lymphoma Treatment

The use of PET scans to assess the response to treatment of lymphomas. Credit: Photo©smaleriegal

How are PET scans used during lymphoma treatment to evaluate (assess) how well the treatments are working?  Can they be used to see if a cancer has responded to treatment?  In looking at the answers to these questions, oncologists often use the phrase "response assessment."

PET Scans in Lymphoma

PET scans are a biological or functional imaging test that shows areas of active tumor in the body. PET scans can be used at many points during lymphoma diagnosis, treatment and long term follow-up.

Read the article on PET Scans in Lymphoma.

Guidelines for Monitoring Treatment Response - Issues

The International Harmonization Project is a group of international experts who have suggested some common guidelines to follow when using PET scans for response assessment after treatment completion. Several issues have been addressed in these guidelines:

PET Scans are a Good Imaging Test to Assess Response

PET scans are more accurate than most other imaging tests for correctly picking up leftover cancer (residual disease) after treatment. Though CT scans and MR scans can pick up tumors (masses) remaining after treatment, they are unable to make out whether these masses actually contain growing cancer cells (active disease.) Some masses may have only fibrosis or dead (necrotic) tissue, and do not mean that any cancer is still present.  PET scans can differentiate between these inactive masses and residual active disease.

  In other words, PET scans can tell if you still have cancer versus just a bunch of leftover scar tissue and dead cells.

Most of the Common Types of Lymphoma Show up Well on PET Scans

Hodgkin lymphoma, diffuse large B-cell lymphomas, and follicular lymphomas make up the majority of lymphomas that occur.

These lymphomas show up well on PET scans and this test should be used for response assessment. Some other lymphomas, like mantle cell lymphomas and some slow growing lymphomas show up less well on PET and the role of PET in these lymphomas is less certain.

PET Scans for Response Assessment Should Be Timed Correctly

Treatment with chemotherapy and radiation often results in temporary inflammatory changes that may show up positive on a PET scan when there is no real disease. These inflammatory changes can take some time to subside. It is recommended that PET scans be performed only after 3 weeks of chemotherapy and/or 8-12 weeks of radiation for the true picture to emerge.

Interpreting PET Scan Uptakes in Different Regions of the Body - False Positives

PET scans sometimes turn up positive in certain areas even when there is no active disease (this is called a ‘false positive’). This happens because some areas with inflammation or infection, or even active normal cells can show up bright on PET scans. In order to interpret PET scans better, some basic points have been suggested to the radiologists reading and interpreting your PET scan. Guidelines have been presented regarding what to consider as positive, how to report lung nodules, bone marrow involvement and liver and spleen involvement.

Should PET Scans Be Done During Treatment?

There is no general agreement among oncologists about whether or not on performing a PET scan during treatment offers any real benefit. It can give us an idea on whether the disease is decreasing (regressing,) but if it turns out that its not – it won't necessarily mean anything can be done or changed at that time. Scans are also difficult to read during treatment as factors such as inflammation can make interpretation of the scans much more difficult and complex.

Waiting to See How Your Cancer Has Responded

Not everyone agrees on the best way to monitor the response of lymphomas to treatment, but what all oncologists know is that this is a difficult time for patients.

  In fact, the anxiety that comes during this waiting period and up until a scan has been ordered and done has been coined "scanxiety."

People all cope with this waiting in different ways.  Some people have found it helpful to ask themselves the question, "What is the worst thing that could happen?"  Our brains tend to immediately think "death" whereas there are often further treatments of some form or another no matter the results of a scan.  Others find it helpful to stay busy, keep a journal, or even reach out to help others.  Sometimes caring for others coping with a similar disease can help take your mind off the "what if's" with your own.  Check out these tips for coping with lymphomas.


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