NHL Cyberfamily

Non-Hodgkin's lymphoma support


Diagnostic imaging

Information about CT and PET scans


Diagnostic imaging

Your doctor may order a variety of different diagnostic scans and tests to help monitor and diagnose your NHL. The variety of different scans is often confusing to patients, and many wonder why they are not getting one type of scan instead of another. The most important point to remember is that each type of scan has its purpose and place in treatment. No one scan type is superior to all the others because each serves a different purpose, and each is very valuable in its own right.

The first topic we will cover however is the recent (2014) recommendations about how and when to use PET/CT when diagnosing, staging and assessing the response for lymphoma.

  1. When should PET or CT be used for staging and response of assessment?
  2. CT - Computed tomography or Computed Axial Tomography
  3. PET - Positron Emission Tomography
  4. How much radiation do I get from these scans?
  5. How often should I have follow up PET/CT scans after treatment is done?

When to use PET/CT for staging and response assessment

CT scans

CT or Computed Tomography (often called CAT for Computed Axial Tomography) is the most common and useful type of scan for regular detection and follow up of NHL. CT's are still just X-ray images but they produce a near 3D image of the interior of the body. They do this by having the scanner spin around the body taking multiple pictures, or slices. A computer combines these images into a single  image that looks like a slice taken right out of your body when looking down from the top of the head.  

CT Scanner

Click here to view a complete CT scan series

CT's are the most widely used scan because they allow the radiologist and doctor to look "inside" your body and see the structures that are there. They can see shape, size, and location of anything inside you. They provide far more detail than a simple x-ray image can. This is extremely important for finding tumours, and monitoring their growth, and seeing if they are threatening any nearby organs. Virtually all patients will undergo multiple CT scans throughout their journey with  NHL. They are relatively inexpensive and give the doctors a great deal of information about what is going on. Even very small tumours can usually be spotted on a CT scan by an experienced radiologist. Since they have been around for a long time, there is a high degree of experience with them in the medical field so mistakes are less likely to happen.


How much radiation am I getting from all these scans?

Looking for more information about the various types of scans? There is a ton of it on the Internet. Just use your favourite search engine to search for "FDG PET", or "Gallium Scintigraphy" or "Computed Tomography". You'll find lots of information.  One question that might occur to many patients is "Just how much radiation do I get from these various scans?"  Of primary concern are X-rays, and CT's since they deliver radiation directly to your body. PET and Gallium scans inject radioactive substances into your body, but in only the most minute quantities. Nevertheless a PET scan delivers approximately the same amount of radiation to the body as a whole body CT scan.  

It is a tough question to answer, but there is no doubt that a CT scan delivers dramatically more radiation to your body than any type of x-ray.  A CT of the chest and abdomen can deliver the equivalent of 300 chest x-rays in radiation.  While that sounds very frightening it is important to understand that this is still a small amount of radiation due to the very sophisticated equipment in use today. However if you are interested in reading a bit more about various radiation doses you get on a regular basis click the links below.

  1. Cancer risks associated with external radiation from diagnostic imaging procedures
  2. Projected Effects of Radiation-Induced Cancers on Life Expectancy in Patients Undergoing CT Surveillance for Limited-Stage Hodgkin Lymphoma: A Markov Model.

  3. Computed Tomography — An Increasing Source of Radiation Exposure; from the New England Journal of Medicine

  4. Ask the Expert - Medical radiation exposure

  5. Radiation Risk from CT scans

  6. Radiation and Risk. How much radiation do we get?

  7. Health Physics Society radiation Q&A

  8. Radiation dose chart

While not quite related to diagnostic imaging the following link looks at the risk of radiation from mobile phones which is still a concern to many people.

Mobile Phone Radiation and Health Guide


What is the role of surveillance scanning after treatment

One question that is always on the mind of patients is, "how often do I need to have follow-up PET/CT scans one I have complete treatment?"  There is no simple answer to that question. It depends a lot on the doctor and patient preference, as well as how well the patient responded to their treatment. If someone achieves a complete remission then follow-up scans might be less frequent than someone who was refractory to treatment.  The need to know if the cancer is gone or has come back, has to be balanced with the risk of unnecessary radiation exposure.

To make this issue more confusing  many recent studies have called into question the value of doing any surveillance scanning at all. Most of these studies have found that patients almost always experience symptoms of a relapse before any PET or CT scan finds it.  This raises the question of whether or not we are doing scans that don't really need to be done, and exposing people to more radiation than necessary. Below are a variety of studies that look at this issue of surveillance scans in the follow up for lymphoma.

  1. Utility of Routine Post-Therapy Surveillance Imaging in Diffuse Large B-Cell Lymphoma

  2. PET/CT in lymphoma surveillance: A large single-center experience

  3. Post-treatment PET scan is highly predictive of outcome (PFS and OS) in MCL pts treated with R-Hyper-CVAD in the frontline setting regardless of MIPI score. 

  4. Utility of surveillance imaging in patients with non-Hodgkin lymphoma.

  5. Value of surveillance studies for patients (pts) with stage I-II diffuse large B-cell lymphoma (DLBCL) in the rituximab (R) era.

  6. Role of routine imaging in detecting recurrent lymphoma: A review of 258 patients with relapsed aggressive non-Hodgkin and Hodgkin lymphoma

  7. Limited clinical benefit for surveillance PET-CT scanning in patients with histologically transformed lymphoma in complete metabolic remission following primary therapy

  8. CT Scans in NHL Surveillance May Cause More Cancers