Ask Question
Sign Guest book

 
About Lymphoma
| Advocacy & Art | CAM & Life Style | Clinical trials | Doctors & Centers  | Guidelines  at  Diagnosis | How  to   Help  | Research | Side Effects  | Support | Symptoms  | Tests | Treatments


WebCasts

PET imaging

  

Tests & Imaging > PET scans

Last update: 02/10/2008

TOPIC SEARCH: PubMed | Medscape

Preparations | PET safetyFalse Positives |  Summary of Uses & Limitations  
Response to TreatmentSUV Reference Range?Resources | Research News

PET stands for Positron Emission Tomography.

therapy1.jpg (27476 bytes)Tumor cells are typically metabolically active and will take up more glucose than normal cells.  PET scans take advantage of this difference to help distinguish normal cells and scar tissue from active lesions.  

The PET tracer (FDG)  has two parts: glucose, and a mildly radioactive component.  As the tracer moves through the body the cells that are active take up the glucose along with the radioactive part of tracer.  

Injecting FDG into your body allows special cameras to show cells that take up excessive glucose - cells such as malignant cells, but also reactive normal cells, that have a higher metabolic rates.

"Although CT and MRI provide high-resolution anatomic information, PET adds information on the metabolic activity of lesions. Standardized uptake values (SUVs) are a measure of the concentration of a radiotracer in a defined region divided by the injected dose normalized for the patient's body weight at a fixed time after tracer injection. 

This functional information may be particularly useful in determining response to therapy, as suggested by the European Organization for Research (25). These metabolic changes may occur even if anatomic size does not change significantly." 2 

More detail on the PET tracer: FDG (Fluro-D-glucose) is a positron emitting radio-pharmaceutical. 
FDG emits beta waves. 
It's half life is about 110 minutes.  

Search for ACR accredited Diagnostic Imaging Centers 

ACR accreditation means: "Your hospital, clinic or health center has voluntarily gone through a rigorous review process to be sure it meets nationally accepted standards.  The personnel are well qualified, through education and certification, to perform and interpret your medical images and administer your radiation therapy treatments. The equipment is appropriate for the test or treatment you will receive, and the facility meets or exceeds quality assurance and safety guidelines."

Preparation may vary at different centers

bullet

Fast before the PET scan as instructed, 

Usually 6 or 8 hours
Water is okay
Do not chew gum during fast period.

bullet

Last meal before the scan?  

High in protein; 
Low in carbohydrates. 

bullet

Ask about use of medication prescribed by your physician -

If required medications are taken with food, ask for instructions.

bullet

Avoid caffeine, sugar, tobacco  for one day prior to your exam.

bullet

Avoid rigorous exercise for one day prior to your exam.

bullet

Do you have diabetes?

Discuss this with your physician and 
Call the center staff 48 hours before your scan.

bullet

Pregnant? or might be?  

Generally, PET and PET/CT scans are not performed on pregnant women.

Adapted from nps.cardinal.com 

 

PET Safety?  "Because the radioactivity is very short-lived, your radiation exposure is extremely low. The substance amount is so small that it does not affect the normal processes of the body." 
Source: radiologyinfo.org   

Also see Comparing Imaging for more detail on exposures.

False Positives?  "It does seem that false positive scans can be obtained but that overall a negative scan is much more informative and is a far more reliable observation. 

False positive scans can occur because of metabolically active tissue taking up the tracer FDG in high concentrations. This may be seen post operatively, in a focus of infection or inflammation." Source:
lymphoma.org.uk

Think Twice Before Exercising When Getting that PET Scan - 
By: Society of Nuclear Medicine | Published: Mar 8, 2006 at 07:01 - yubanet.com/
 
"Any type of physical activity - from tapping your feet while in the waiting room to jogging the neighborhood the day before - can affect the results of a PET scan and lead to false-positive results," said Medhat M. Osman, M.D., ScM, Ph.D 

The study advises technologists to instruct the patients to minimize muscle activity during the uptake phase and to telephone patients ahead of their appointments to advise them to refrain from any excessive muscle activity at least 48 hours before a PET scan.

Brown fat and false positives?  
 
" the phenomenon of 18F-FDG uptake in brown fat was first discovered when PET/CT fusion images showed 18F-FDG concentration in the adipose tissue rather than in muscle or lymph node as previously assumed."   http://jnm.snmjournals.org/cgi/content/full/45/1_suppl/72S#F4 

Summary of potential uses of PET

Also see New PET Guidelines for Assessment of Response to Lymphoma Treatment CME (2007)
Medscape  (free login required)  

AND: Studies Assessing the Utility of PET (in table format) ncbi.nlm.nih.gov

==

"One of the most important skills in PET reporting may be to recognize its limitations and be clear when a definitive answer cannot be given to the referring physician's question"    

- Barrington, O'Doherty: EJNM 2003:30, suppl. 1: S117-S127

Notes taken from a presentation by Paul A Hamlin, MD:

bullet

Staging, such as to verify localized disease? 
(experimental; utility varies with subtype of lymphoma)

bullet

Distinguishing indolent from aggressive histology based on SUV measurements? 
(experimental - not a substitute for pathologic confirmation from a biopsy)
bullet

Guiding location of lesion to biopsy? 
(could be useful when transformation from indolent to aggressive is suspected)

bullet

PET visualizes follicular lymphoma irrespective of grading
Ann Oncol. 2006 May;17(5):780-4. Epub 2006 Feb 23. PMID: 16497824 | Related articles

bullet

Majority of Transformed Lymphomas Have High SUVs on PET Scanning Similar To 
Diffuse Large B Cell Lymphoma (DLBCL) - ASH 2006 

"... transformation to aggressive lymphoma should be suspected in patients with indolent 
lymphoma found to have high SUVs on FDG PET, and biopsies should be directed to the 
site of greatest PET avidity whenever feasible."

bullet

Predicting response to treatment early? 
(experimental; false positives are possible; probably limited to curative diseases, such as  DLBCL, Hodgkins) 
 TRIAL SEARCH: ClinicalTrials.gov: 

bullet

Evaluating residual masses following treatment 
(common - biopsy may be required if aggressive interventions are to be used)

bullet

Bone marrow evaluations? 
(sub optimal - MRI is better)

bullet

Follow up/monitoring? 
(limited information, may be useful in select patients with usual sites of disease)

Source: Paul A Hamlin, MD - presentation

 

Summary of limitations:  

bullet

Some indolent lymphomas may show only low-grade FDG uptake, 

bullet

FDG uptake is non-specific (other pathology, inflammations, infections, HIV, etc),  

bullet

Clinical limitations of findings

Source: Paul A Hamlin, MD - presentation

 

Response to treatment evaluations:  

"Specifically, assessing response [with PET] may be useful in two possible situations: 

(1) to evaluate tumor response at the end of a full course of treatment, or 

(2) to predict tumor response early in the course of a prolonged treatment regimen [for aggressive lymphomas]. In the first instance, early detection of treatment failure may permit a physician to institute a second-line therapeutic approach. 

In the second instance, accurately predicting treatment failure may allow the physician to substitute an alternative regimen, without subjecting the patient to the toxicity of the full course. "  Peter E. Valk, MD

TRIAL SEARCH: ClinicalTrials.gov: 

Also see: PET Predicts Lymphoma Treatment Outcome - interactive.snm.org
" The authors concluded that PET was a better predictor of outcome and response to therapy after just one cycle of chemotherapy than after completion."

AND PET Scan More Accurate Predictor of Outcome in [aggressive] Non-Hodgkin’s Lymphoma -  cancerconsultants.com
 
 

End of treatment evaluations

"PET is very accurate in predicting short-term treatment failure. However, it cannot detect microscopic residual disease and thus its value is hampered by false negative results in patients relapsing later. 

On the other hand, a biopsy is always indicated before salvage therapy in order to exclude false positive PET results related to inflammatory lesions or to second primary tumors." ~ G. H. M. Jerusalem, et al. - ASCO presentation 

Also see: 

bullet

Limitations of PET for imaging lymphoma. Eur J Nucl Med Mol Imaging. 2003 Jun;30 Suppl 1:S117-27. Epub 2003 May 13. Review. PMID: 12748831
 

bullet

Predictive value and diagnostic accuracy of PET treated grade 1 and 2 follicular lymphoma. 
Leuk Lymphoma. 2007 Aug;48(8):1548-55. PMID: 17701586 

Our results indicate that PET is accurate in the diagnostic assessment of treated FL-1 and FL-2 
and, post-treatment PET positive patients are likely to relapse prior to PET negative patients.


 

PET Standard Uptake Values (SUV) and proliferation rates in lymphoma

NOTE:  Differences in administration and tracers across centers may influence SUV values. 
That is, we don't know if the SUV values and reference ranges are comparable in different centers.

study: Molecular imaging of proliferation in malignant lymphoma.
Cancer Res. 2006 Nov 15;66(22):11055-61. PMID: 17108145 

(PET) with the thymidine analogue 3'-deoxy-3'-[(18)F]fluorothymidine (FLT)

standardized uptake values (SUV) and correlated to tumor grading and 
proliferation fraction as determined by Ki-67 immunohistochemistry

11 patients with indolent lymphoma, mean FLT-SUV in biopsied lesions was 2.3; range, 1.2 - 4.5

21 patients with aggressive lymphoma, mean FLT-SUV, 5.9; range, 3.2 - 9.2

study: Majority of Transformed Lymphomas Have High SUVs on PET Scanning Similar To Diffuse Large B Cell Lymphoma (DLBCL). Session Type: Poster Session, Board #580-II 


The SUVmax for a transformed aggressive lymphoma ranged from 3.2 - 30.2
with a median of 10.8 and mean of 14. 

16/28 (57%) patients had an SUVmax above 10; and 12/28 (43%), above 13.

study: Lapela et al. (1995b) University of Turko, Turko, Finland, and University of Helsinki, 
Helsinki, Finland 


Prospective study 22 subjects (small study) with untreated biopsy proven NHL, including 7, 11, and 4 with low, intermediate, and high-grade lymphomas, respectively 

Median SUV and rMRg for tumors: 8.5 and 22.7 F mol/100/g/minute, respectively.

Significant correlation between histologic tumor grade and FDG uptake (both SUV and rMRg) when using Working Formulation and Kiel classification systems but not when using Ann Arbor classification system. 

Significant association between FDG uptake and S-phase fraction, an indication of tumor grade.

Review article on PET to determine grade  - Medscape free login req. 

...  He concludes that the SUVs are most helpful in the high and in the low ranges. That is, an SUV > 13 is highly suggestive of an aggressive lymphoma, and an SUV < 6 is most compatible with an indolent lymphoma. Only 8% of patients with aggressive lymphoma had SUV < 6, and 6% of patients with indolent lymphoma had SUV > 13. 

However, these upper and lower cutoff values applied to only 55% of the patients studied. In other words, 45% of the patients had SUV between 6 and 13. In these, the overlap was sufficient to preclude a confident assessment of tumor type based on SUV. Using an SUV of 10 as an absolute cutoff results in a 29% misclassification rate for aggressive NHL and 19% for indolent NHL. This could result in undertreatment of many patients with aggressive lymphomas and overtreatment of many with indolent lymphomas."

 

Resources:

  1. About PET - Cancer Help Org  | Fact file on PET - lymphoma.org.uk
    Technical details, such as exposure to organs - petnetpharmaceutical.com PDF 
  2. Studies Assessing the Utility of PET (in table format) ncbi.nlm.nih.gov
  3. The Role of PET in Lymphoma*  ~ Yuliya S. Jhanwar1 and David J. Straus2 
     - jnm.snmjournals.org full text 
  4. Clinical Applications of P.E.T. in Oncology” Conference Vancouver, B.C.  June 11, 2001 - petscan.ca
  5. Accuracy of end of treatment 18F-FDG PET for predicting relapse in patients with Hodgkin's disease (Hd) and non-Hodgkin's lymphoma (Nhl) - ASCO 
  6. Assessing response to therapy:
    bullet
    Aggressive NHL: PET Scan More Accurate Predictor of Outcome in 
    Non-Hodgkin’s Lymphoma -  cancerconsultants.com
    bullet
    Aggressive NHL: Early FDG-PET assessment in combination with clinical risk scores determines 
    prognosis in relapsed lymphoma - bloodjournal.org 
    bullet
    Assessing Therapy Response with FDG PETPET can help determine when and if additional 
    treatment for tumors is in order. - Peter E. Valk, MD 
    bullet
    Hodgkin's: Substantial impact of FDG PET imaging on the therapy decision in patients with early-stage 
    Hodgkin's lymphoma. Br J Cancer. 2004 Feb 9;90(3):620-5. PMID: 14760374 | Related articles
    bullet
    Prognostic value of FDG-PET scan imaging in lymphoma patients undergoing autologous stem cell transplantation. Bone Marrow Transplant. 2006 Jun 12; PMID: 16770314 

    A positive FDG-PET scan after salvage chemotherapy and prior ASCT indicates an extremely poor 
    chance of durable response after ASCT.
  7. Lymphoma Diagnosis and Treatment: CHOP, MALT, PET, and More - Medscape (free login, req.)
  8. Improving management of Lymphoma with - Dimag.com
  9. Comparing PET and Gallium scans for NHL - Above
  10. Frequent impact of positron emission tomography on the staging of patients with indolent non-Hodgkin's lymphoma - racp.edu.au
      
    Conclusion: "These findings demonstrate that 18FDG-PET has a high sensitivity for indolent NHL, and often leads to alteration of disease stage and management. This high accuracy of 18FDG-PET in assessing discordant lesions suggests a greater diagnostic utility when compared with CT."
  11. Advantages of positron emission tomography (PET) with respect to computed tomography in the follow-up of lymphoma patients with abdominal presentation. Leuk Lymphoma. 2002 Jun;43(6):1239-43. PMID: 12152991- PubMed
  12. PET for MALT?
    bullet
    PET in mucosa-associated lymphoid tissue (MALT) lymphoma.
    Leuk Lymphoma. 2006 Oct;47(10):2096-2101. PMID: 17071482 | Related articles 

    This study retrospectively enrolled 26 patients with known active disease. 18F-FDG-PET was true 
    positive (TP) in 21/26 patients and false negative (FN) in 5/26. Sensitivity of 18F FDG-PET 
    for extra-nodal MALT was 81%. The data show that 18FDG-PET is a useful diagnostic tool in 
    order to stage, restage or monitor disease in patients with extra-nodal MALT lymphoma.
    bullet
    Positron emission tomography with fluorine-18-2-fluoro-2-deoxy-D-glucose (F18-FDG) does not visualize extranodal B-cell lymphoma of the mucosa-associated lymphoid tissue (MALT)-type 

    Annals of Oncology, Vol 10, Issue 10 1185-1189, Copyright © 1999 by European Society for Medical Oncology  - annonc.oupjournals.org

    BUT a patient with MALT reports:  "My most recent PET scan (last week) showed my indolent 
    malt active in its original site; eg: stomach and a new occurrence in my mouth, sublingually. "  
    So this finding might not apply to every situation.
    bullet
    FDG-PET scanning for detection and staging of extranodal marginal zone lymphomas of the MALT type: a report of 42 cases - annonc.oupjournals.org 
  13. Whole Body FDG PET in the Evaluation of Lymphoma - 
    Kavitha Vadde, MD Alan J. Fischman, MD, PhD Yr. 2000
  14. Review article on PET to determine response to treatment and grade  - Medscape free login req. 

     

Research News:

bullet
Response Assessment of Aggressive Non-Hodgkin's Lymphoma by Integrated International Workshop Criteria and Fluorine-18-Fluorodeoxyglucose Positron Emission Tomography. J Clin Oncol. 2005 Apr 18; PMID: 15837965
bullet
Use of PET (18F-FDG positron emission tomography) following allogeneic transplantation to guide adoptive immunotherapy with donor lymphocyte infusions. Br J Haematol. 2005 Mar;128(6):824-9. PMID: 15755287
bullet
Intensity of 18Fluorodeoxyglucose Uptake in Positron Emission Tomography Distinguishes Between Indolent and Aggressive Non-Hodgkin's Lymphoma. J Clin Oncol. 2005 Apr 18; PMID: 15837966
bullet
Positron emission tomography (PET) with 18F-fluorodeoxyglucose (18F-FDG) for the staging of low-grade non-Hodgkin's lymphoma (NHL). Ann Oncol. 2001 Jun;12(6):825-30. PMID: 11484959 - PubMed
bullet
Assessment of tumor burden and treatment response by 18F-fluorodeoxyglucose injection and positron emission tomography in patients with cutaneous T- and B-cell lymphomas. J Am Acad Dermatol. 2002 Oct;47(4):623-8. PMID: 12271315
 
Disclaimer:  The information presented on Lymphomation.org is not intended to be a substitute for 
professional medical advice or to replace your relationship with a physician.
For all medical concerns,  you should always consult your doctor. 
Patients Against Lymphoma, Copyright © 2004,  All Rights Reserved.