Hi narbguy-ga, and thanks for your question.
As usual, this is not a substitute for medical advice or direct
medical evaluation and treatment.
There was a very recent study looking at the utility of PET scans in
patients with non-Hodkin's Lymphoma immediately following chemotherapy
to evaluate response.
Haioun C, Itti E, Rahmouni A, Brice P, Rain JD, Belhadj K, Gaulard P,
Garderet L, Lepage E, Reyes F, Meignan M.
[18F]fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET)
in aggressive lymphoma: an early prognostic tool for predicting
patient outcome. Blood. 2005 Aug 15;106(4):1376-81. Epub 2005 Apr 28.
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15860666&query_hl=11&itool=pubmed_docsum
This article is not freely available online, however, you can request
a free reprint from Dr. Haioun:
corinne.haioun@hmn.aphp.fr
The study's ultimate conclusion was that "[p[redictive value of "early
PET" was observed in both the lower-risk and higher-risk groups,
indicating prognostic independence from the IPI [International
Prognostic Index]. Therefore, FDG-PET should be an early guide to
first-line strategies in aggressive lymphoma."
This group also discusses the utility of CT:
"Obtaining a complete remission (CR) after first-line chemotherapy is
of paramount importance in patients with aggressive non-Hodgkin
lymphoma because it usually leads to a longer progression-free
survival, whereas an incomplete response is usually associated with a
poorer outcome.[1] Standardized criteria for response assessment have
been proposed by Cheson and colleagues [2] to ensure comparability
among clinical trials, with these criteria relying mostly on
measurement of tumor size using computed tomography (CT). However, in
the presence of a residual mass, anatomic imaging is not optimal for
discriminating active disease from fibrosis, and the positive
predictive value of CT may be as low as 40%.[3-5] This led to the
concept of "complete remission uncertain" (CRu), which reflects the
unknown significance of persistent radiologic abnormalities in
patients who, otherwise, seem to be in CR."
By comparison, PET is a better study with respect to detecting recurrent disease:
"By contrast, functional nuclear imaging provides metabolic tissue
characterization, which is potentially more useful for response
assessment after first-line chemotherapy. The emergence of
[18F]fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET)
in the clinical armamentarium and its increasing availability have
recently provided an alternative to [67Ga]gallium-citrate scan, which
was previously used to detect residual active disease despite poor
spatial resolution and low sensitivity at the abdominal level.[6] With
FDG-PET, several studies have demonstrated that persistence of an
increased glycolytic activity in lymphoma lesions, that is,
persistence of a positive scan at the end of first-line therapy, was
associated with a 100% relapse rate, whereas the latter ranged from
16% to 20% in case of negative scan.[3-5]"
They also compare PET with the current standard, which is IPI
(International Prognostic Index):
"Multiagent chemotherapy regimens have transformed aggressive lymphoma
from a fatal disease to a potentially curable one, but no more than
half of all patients are cured.[7] More aggressive, but also
potentially more toxic, treatments are now available; thus, there is
an increasing interest for early patient selection, assuming that
rapid responders to a standard induction are likely to show better and
more durable response, whereas nonresponders could benefit from an
early change of therapeutic orientation. The International Prognostic
Index (IPI),[8] a well-established predictor of outcome in aggressive
lymphoma, is based on 5 pretherapeutic clinical characteristics:
patient's age, Ann Arbor stage, serum lactate dehydrogenase level,
performance status according to the Eastern Cooperative Oncology Group
(ECOG) scale, and number of extranodal sites. However, recent gene
profiling studies have shown that gene expression signatures can be
used to predict the prognosis, independently from the IPI, a feature
that may reflect the biologic heterogeneity observed in diffuse large
B-cell lymphoma.[9,10] In this respect, if FDG-PET could prove useful
as an early indicator of tumor chemosensitivity, it might also reflect
the heterogeneity of the disease better than the IPI and may help
refine therapeutic strategies."
Finally, this group looked at survival of PET positive and PET
negative groups, split according to their IPI category. In other
words, one would expect the IPI intermediate or high risk patients to
do poorly and the IPI low risk patients to do better.
Correspondingly, one would expect that the IPI low risk patients
should be PET negative and vice versa, if the IPI system is accurate.
It turns out that for both high and low IPI risk categories, there are
a good number of PET positive and PET negative patients, which
correlated better with survival than the current IPI standard. You
can take a look at the graph from the paper here:
http://img404.imageshack.us/img404/5685/zh801605825600047gj.jpg
So, in short, PET is a better test for detection of recurrent
non-Hodkin's Lymphoma. Having said this, one issue in the US is
insurance reimbursement. Having been burned by the high utilization
of other imaging modalities (e.g. CT, MRI), insurance companies have
been keeping a tight cap on reimbursement for PET scans. Fortunately,
restaging or evaluation of response to treatment is one of the covered
"indicated" conditions. You can read more here:
http://www.petscaninfo.com/zportal/portals/phys/reimbursement/clinical_indications
====================
I hope this information is helpful. I wish you the best in your
battle with this disease. Please feel free to request clarification
prior to rating.
Best,
-welte-ga |
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