Preparations
| PET
safety | False Positives
| Summary of Uses & Limitations
Response to Treatment | SUV Reference Range? | Resources
| Research News
PET stands
for Positron Emission
Tomography.
 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
 |
Fast before
the PET scan as instructed,
Usually 6 or 8 hours
Water is okay
Do not chew gum during fast period.
|
Last meal before
the scan?
High in protein;
Low in carbohydrates.
|
Ask about use of
medication prescribed by your physician -
If required medications are taken with food, ask for
instructions.
|
Avoid
caffeine, sugar, tobacco for one day prior to your exam.
|
Avoid rigorous
exercise for one day prior to your exam. |
|
Do you have diabetes?
Discuss this with your physician and
Call the center staff 48 hours before your scan.
|
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:
|
Staging,
such as to verify localized disease?
(experimental; utility varies with subtype of lymphoma) |
|
Distinguishing
indolent from aggressive histology based on SUV
measurements?
(experimental - not a substitute for pathologic confirmation
from a biopsy)
 |
Guiding
location of lesion to biopsy?
(could be useful when transformation from indolent to
aggressive is suspected) |
|
PET
visualizes follicular lymphoma irrespective of grading.
Ann Oncol. 2006 May;17(5):780-4. Epub 2006 Feb 23. PMID:
16497824 | Related
articles |
|
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."
|
|
|
Predicting
response to treatment early?
(experimental; false positives are possible; probably limited to
curative diseases, such as DLBCL, Hodgkins)
TRIAL SEARCH: ClinicalTrials.gov: |
|
Evaluating
residual masses following treatment
(common - biopsy may be required if aggressive interventions are
to be used) |
|
Bone
marrow evaluations?
(sub optimal - MRI is better) |
|
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:
|
Some
indolent lymphomas may show only low-grade FDG uptake, |
|
FDG
uptake is non-specific (other pathology, inflammations,
infections, HIV, etc), |
|
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: - 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:
|
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
|
|
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:
-
Studies Assessing the Utility of PET (in table
format) ncbi.nlm.nih.gov
The Role of PET in Lymphoma* ~ Yuliya S. Jhanwar1 and David J. Straus2
- jnm.snmjournals.org
full text
Clinical
Applications of P.E.T. in Oncology” Conference Vancouver, B.C.
June 11, 2001 - petscan.ca
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
Assessing response to therapy:
| Aggressive NHL: PET Scan More Accurate Predictor of Outcome
in
Non-Hodgkin’s Lymphoma - cancerconsultants.com
|
| Aggressive NHL: Early FDG-PET assessment in
combination with clinical risk scores determines
prognosis in relapsed lymphoma - bloodjournal.org
|
| Assessing
Therapy Response with FDG PETPET can help determine when and if
additional
treatment for tumors is in order. - Peter E.
Valk,
MD
|
| 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
|
| 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.
|
Lymphoma
Diagnosis and Treatment: CHOP, MALT, PET, and More
- Medscape
(free login, req.)
Improving
management of Lymphoma with - Dimag.com
Comparing PET and Gallium scans for NHL - Above
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."
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
PET for MALT?
| 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.
|
| 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.
|
|
FDG-PET scanning for detection and staging of extranodal
marginal zone lymphomas of the MALT type: a report of 42 cases -
annonc.oupjournals.org
|
Review article on PET to
determine response to treatment and grade - Medscape
free login req.
Research News:
|
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
|
|
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
|
|
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
|
|
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
|
|
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
|
|
