Overview of Nuclear Medicine PET/CT Lymphomas Assessment, Protocols, and Interpretation
Positron emission tomography, or PET, is a special type of scan that doctors use to help diagnose and check the status of a variety of illnesses, including cancer, neurological conditions, heart problems, and even infections. Unlike scans like CT or MRI—which mostly show the physical structure of the body—PET lets doctors see what’s happening at the cellular level. This is really important because it can help doctors to pinpoint areas of the body where cells aren’t working properly, even before there are physical signs of a problem.
One of the ways doctors use PET scans is in conjunction with CT scans—a type of x-ray that shows the body in layers. This combination, known as PET-CT, gives doctors a way to see both the structure and the function of tissues and organs, making it particularly useful when treating cancer.
There are many types of PET scan, which use different chemicals (called radiotracers) according to what they’re trying to uncover. The most common tracer is a type of artificially created sugar called F18 fluorodeoxyglucose (FDG). FDG is used in PET scans to help doctors diagnose and manage conditions like cancer since cancer cells tend to use more sugar than normal cells.
This information aims to explain how the PET-CT scan that uses FDG, known as an FDG PET/CT, is specifically used in the management of a type of cancer known as lymphoma.
Anatomy and Physiology of Nuclear Medicine PET/CT Lymphomas Assessment, Protocols, and Interpretation
Lymphomas are various types of disorders that cause an abnormal growth in lymph nodes or other tissues related to the immune system. This basically means, cells that should be defending your body start growing uncontrollably. While lymphoma, a kind of cancer, can start from any part of the body, it usually starts in the cells or precursors of the immune system. There are two main categories of Lymphoma: Hodgkin Lymphoma (HL) and non-Hodgkin Lymphoma (NHL), with NHL being more common.
Breaking it down further, Hodgkin Lymphoma gets divided into classical and nodular lymphocyte-predominant lymphoma. The classical type is more common and has four different subtypes, while non-Hodgkin lymphoma is grouped into aggressive or slow-growing, also called indolent, lymphomas. An aggressive type of NHL is the diffuse large B cell lymphoma. A less common aggressive type is the mantle cell lymphoma. For the slow-growing types, you find follicular, marginal zone, and small-cell lymphocytic lymphomas.
The World Health Organisation (WHO) formed a classification in 2017 and divided lymphoma into three main categories: NK T-cell lymphoma, B-cell lymphoma, and HL. Interestingly, the slow-growing (indolent) lymphomas can become aggressive during the disease progression. That’s why, to evaluate the tissue properly, a biopsy, which is a small procedure to remove tissue for examination, is suggested. The tissue evaluation, obtained with a needle, is not enough for optimal grading of the disease.
Why do People Need Nuclear Medicine PET/CT Lymphomas Assessment, Protocols, and Interpretation
Identifying the stage of lymphomas, a type of cancer that starts in the cells of the body’s immune system, is essential for providing the best treatment and understanding the patient’s prognosis. Traditionally, doctors have used an imaging test called a CT scan to determine the level of spread and shape of the cancer. One limitation of the CT scan is that it mainly focuses on the size of the lymph node, which is a small structure of the immune system where cells fight infections. CT scans also have limited ability to spot extranodal disease, which is when lymphoma spreads to areas outside of the lymph node, and disease affecting the liver, spleen and other parts of the body.
Nowadays, doctors use a mix of another imaging test called FDG PET/CT that enables a more comprehensive view of the body and can better reveal smaller lesions or abnormalities not visible in CT scans. FDG PET/CT is also more effective in spotting disease that has infiltrated the bone marrow, the spongy tissue inside your bones, the lungs and parts of the digestive system. However, this test may not be as useful in the staging process of indolent lymphomas, which grow slowly. FDG PET/CT is exceptionally good at detecting when these slow-growing tumors have transformed into a more aggressive disease.
FDG PET/CT is also highly efficient at checking the progress of treatment by showing any remaining active disease after treatment is complete. It helps doctors distinguish between remaining disease and normal post-treatment changes. Scans can also be done midway through chemotherapy to indicate if the treatment is effective, even before it has had a significant effect on the size of the tumor. This is often a good predictor of full recovery.
The Lugano classification system, developed by a group of various medical specialists in Lugano, Switzerland, uses a 5-point score based on the results of FDG PET/CT to assess patient’s response to treatment. It ranges from 1, which means no uptake or absorption of the tracer used during the test, to 5, which reflects high uptake or absorption pointing to active disease. The lower scores denote that the patient has responded positively to treatment, while the higher scores suggest ongoing disease activity.
Because PET/CT scans can sometimes falsely indicate disease, they are not normally used to detect recurrent disease in patients in remission, unless the patient starts showing symptoms. Despite this, the test remains a vital tool in assessing a patient’s response to treatment.
When a Person Should Avoid Nuclear Medicine PET/CT Lymphomas Assessment, Protocols, and Interpretation
There are no strict reasons why a person can’t have an FDG PET/CT scan, which is a type of medical imaging test. It’s very uncommon for someone to have an allergic reaction to the FDG used in the scan.
Usually, PET scans are done without using a contrast dye. However, sometimes the CT part of the scan is done using an iodine contrast dye. This dye is used to highlight certain parts of the body on the scan. If someone is allergic to iodine, special precautions need to be taken when doing the PET/CT scan.
If a PET/CT scan needs to be done on a pregnant person, the potential risks and benefits should be carefully considered and discussed before going ahead with the scan.
If a person doesn’t follow the required preparation instructions for the PET/CT scan, it may be better to reschedule the test until they can meet these preparation conditions.
Equipment used for Nuclear Medicine PET/CT Lymphomas Assessment, Protocols, and Interpretation
FDG PET/CT is a test that happens on a specific type of machine called a scanner. This test requires getting a special substance called FDG injected into your vein, so a small, thin tube (known as intravenous access) is needed. The amount of this substance used, called a radiotracer, is typically between 8 to 15 mci (millicuries). Sometimes, another substance (called a contrast) is given orally (by mouth) or through your veins depending on the instructions (or protocol) of the test.
Who is needed to perform Nuclear Medicine PET/CT Lymphomas Assessment, Protocols, and Interpretation?
An expert, known as a nuclear medicine technologist, is responsible for giving you the injection required for the test, capturing the necessary images, and handling the information collected. Afterward, a specialist doctor either a nuclear medicine physician or a nuclear radiologist, who are trained in interpreting these types of medical images, will study the results to understand your health condition better.
Preparing for Nuclear Medicine PET/CT Lymphomas Assessment, Protocols, and Interpretation
FDG, which is similar to the sugar glucose, is used in certain medical scans. However, too much regular glucose (sugar) in the body can interfere with these scans, making them less clear or even useless. Because of this, patients should not eat or drink anything for 4 to 6 hours before getting the FDG injection. Additionally, we don’t recommend types of food or fluids that contain dextrose, a form of glucose, during this timeframe. It’s also essential to check blood sugar levels before the injection to ensure they’re not too high.
If a patient’s blood sugar level is above 200, unfortunately, they may have to reschedule their appointment. During this fasting period, patients should also avoid chewing gum, as it might contain sugar, and the act of chewing itself can cause the body to absorb more FDG in certain muscles.
People with diabetes who depend on insulin should be aware that taking insulin right before the FDG injection can also affect the scan. It can lead to more FDG being absorbed by the muscles and less by tumors, making the scan less effective. Therefore, we recommend that diabetic patients avoid long-lasting insulin for 12 hours before the injection, and short-lasting insulin 1 to 2 hours before. If possible, these patients should have their appointment in the morning.
To optimise the quality of the scan, patients should refrain from rigorous physical activity 24 hours prior. Exercise can increases FDG absorption in muscles, which can interfere with the scan. Patients should also keep warm and try to relax during the scan and injection process, as cold and tension can affect the test results. We provide warm blankets to keep patients comfortable and avoid this. Furthermore, it’s important for patients to stay hydrated.
Lastly, if a woman is of childbearing age, it is essential to find out if she is pregnant before the scan, according to the rules of the medical institution. This is because such scans may not be safe for pregnant women.
How is Nuclear Medicine PET/CT Lymphomas Assessment, Protocols, and Interpretation performed
The procedure listed involves FDG, or fluorodeoxyglucose, which is a substance similar to glucose, or sugar. You’ll get an injection of FDG, and then the doctors will take pictures of your entire body, from the top of your head to your feet, about an hour to an hour and a half later.
What’s important about FDG is that it enters the body’s cells in the same way glucose does. Just like glucose, once inside a cell, FDG gets transformed into another substance, FDG-6-phosphate. However, unlike the transformed glucose, FDG-6-phosphate doesn’t get used up further by the cell. Instead, it stays in the cell. Now, here’s the interesting part: cancer cells often use more glucose and have more activity of the enzymes that transform glucose, so they take up more FDG. This means that, typically, cancer cells will show more FDG, and this is measured by something called the Standardized Uptake Value (SUV).
In addition to this, FDG is attached to Fluorine-18, a radioactive element. This stuff is created in a machine called a cyclotron and has a lifespan of about 110 minutes. This allows it to be transported from the cyclotron to the location where the PET scan is performed. After it’s injected into you, it spreads throughout your body and emits a tiny particle that interacts with an electron in your body, creating two powerful bursts of energy. The PET scan machine can detect these energy bursts, and this data is used to create the images that your doctors will look at.
In gist, this is exactly how doctors can create detailed images of what’s going on inside your body, especially to detect and study cancer cells.
Possible Complications of Nuclear Medicine PET/CT Lymphomas Assessment, Protocols, and Interpretation
Sometimes, PET/CT scans may show “false positives”– this means the scans indicate something is wrong when it isn’t. Certain conditions or factors can trigger this, and it’s important for doctors reading the scans to understand these.
For instance, inflammation and infection can make areas of the body look different on the scan, which can sometimes be confused for cancer. One such situation can happen with a condition called chronic granulomatous disease. This disease can make certain spots on a scan, usually in the chest area, look bigger and mimic a type of cancer called lymphoma.
Another thing that can confuse scan results is the uptake of energy by a type of body fat called brown adipose tissue (BAT). BAT can look like swollen glands (lymph nodes) on a scan, which might be mistaken for cancer. Certain medications and keeping warm can help reduce the amount of energy BAT takes up, which can make scans clearer.
The drug granulocyte colony-stimulating factor (GCSF) can also affect scan results. GCSF is given to some chemotherapy patients to help their bodies produce more white blood cells. However, it can temporarily cause parts of the body like the bone marrow and spleen to look different on scans. To avoid confusion, it’s suggested to wait two weeks after giving GCSF before doing a follow-up scan.
In young people and kids, an enlarged thymus–an organ located in the chest–can also sometimes be mistaken for disease on a PET/CT scan. Chemotherapy can enlarge the thymus as a side effect, which is normal and doesn’t require extra treatment.
What Else Should I Know About Nuclear Medicine PET/CT Lymphomas Assessment, Protocols, and Interpretation?
Lymphoma is the most common blood cancer around the world. This type of cancer comes in various types, but the most frequent one is called non-Hodgkin’s lymphoma. This type alone ranks as the seventh leading reason for cancer in the U.S., making up 4.2% of all cancer cases. Hodgkin’s lymphoma, another subtype, accounts for about 0.4% of all cancers.
There are several risk factors associated with getting lymphoma. These include being older, although Hodgkin’s lymphoma can also develop in younger people. Other risk factors include having a family history of lymphoma, having an autoimmune disease, being infected with the Human Immunodeficiency virus (HIV), and having been exposed to chemicals like insecticides or radiation at work.
Selecting the best treatment for lymphoma is crucial and depends greatly on the precise staging of the disease and careful monitoring of its progress. A tool called FDG PET/CT has been found very helpful in managing patients with aggressive lymphomas. It is much better than standard CT scans in detecting when the lymphoma has spread to other parts of the body like the bone marrow, liver, spleen, intestines, lungs, and the head and neck areas. If the cancer has spread to these areas, it typically indicates a worse prognosis or outcome.
After starting treatment, the FDG PET/CT also aids in tracking the disease’s response to the treatment. That’s because changes in metabolism in the cancerous cells often occur before any noticeable shrinkage of the tumor size. Patients who show a positive response on an interim FDG PET/CT scan are often more likely to be fully disease-free by the end of their treatment.
This tool is also helpful in evaluating the amount of cancer present in the body, both quantitatively and semi-quantitatively. It does this by assessing three factors: the standardized uptake value (a measure of how much radioactive tracer the tumor cells absorb), the tumor volume, and the total lesion glycolysis relating to energy production in cancer cells.
