Positron emission tomography (PET) uses radioactive tracers like fluorodeoxyglucose (FDG) to detect cancer cells in the body and can help stage and monitor gastrointestinal malignancies, though it has limitations for small or early lesions; PET is useful for detecting metastasis and predicting response to chemotherapy but is not adequate alone for local tumor staging; While PET provides valuable information, it works best as part of a multimodality approach using other imaging techniques.

1. Positron Emission
Tomography in
Gastrointestinal
malignancies
SHANKAR ZANWAR

2. History and principle
 While 1st human PET image was made in 1950, Michael Phelps in
1975 was first to detail the medical importance of PET scan
 PET uses compounds that closely resemble natural substances
like glucose - Fluoro-Deoxy Glucose(FDG)
 These are labelled with radioactive atoms like fluorine (18F) 
emits positrons
 Positron collide with nearby e- , to form ƴrays at diametrically
opp. direction that are detected & localized detector gantry.

3.  After FDG injection activity of patient is restricted for at
least 20 min. to minimize the uptake by sk. muscles.
 PET can be fused with CT to give a better localization of
pathology
 The up take of contrast is quantified in SUV-
Standardized uptake value
 Warburg effect – Cancer cells utilize more glucose and
differently so from normal cells and are not ATP efficient.

4. Esophageal carcinoma
 Role of PET in staging
 Deeper tumor a/w with higher nodal and distant mets
 Nodal mets beyond loco-regional – unresectable
 T2 or less  primary resection, T3 and beyond  pre-op
chemo/chemo-radiotherapy
 Sensitivity of PET in various studies to detect T1 lesion range
from – 43%- 55%.
Kato Cancer 2005
 Larger lesions can be picked up with greater sensitivity

5.  Conclusion from the various studies – PET is inadequate modality for
assessing the tumor depth
 PET cannot distinguish carcinoma in situ from invasive disease
 Also false +ve results may occur d/t chemo, radiation induced
esophagitis, candidiasis
 EUS is a better modality depth assessment 90% sens, 99% specific,
but it may not able to pass stenotic tumors – PET-CT may be useful
here
 Puli WGJ – EUS staging for esop can, metaanalysis 2005

6. Role of nodal staging in
esop. ca
 CT, EUS and PET in synergy
did not improve yield
 Low yield could be d/t
selection bias (only early
stages with micromets)
 PET role – better as adjunct
to conventional imaging
than a comprehensive test

7.  PET combined with CT showed greater accuracy
compared with PET alone (sensitivity 70% vs 62%)
Roedl et al Abd Imaging 2009
 Dual time PET may help differentiating benign vs
malignant lesions

8. Role in detecting mets in
esoph ca
 Better results than in depth
detection
 PET correctly upstaged 15-
20% of pt. from M0 to M1
in studies detecting distant
mets by Flamen et al and
Lowe et al

9. Prediction of survival in
esoph ca
 Meta- analysis of 12 studies reported higher SUV max
was a/w inferior survival
 Hazard ratio for recurrence and death when SUV was
above median – 2.52 and 1.86 respectively
Pan L, Eur J Gasent and Hep 2009
 Survival for 5 year SUV max, Sq C C (contrast with
adeno ca.)
 <4.5 - 76%
 >4.5 – 47% Kato Cancer 2005

10. Role in predicting chemo-
radio reponse
 Mandard system of evaluation after neoadjuvant
chemo–
 >10% tumor cells remnant – non responder
 0-10% - partial response
 0% - complete response
 Ott et al (J Clin Onco – 2006), metabolic responders
(defined as 35% ↓ from base line SUV) were a/w
pathologic response in 44% of pts. compared with 5%
metabolic non responders
 Confirmed similarly by van Vliet ,Br J cancer 2007

11.  Primary utility of change in SUV from baseline response
to chemo is guides in future management.
 MUNICON trial metabolic responders achieved higher
histological response in 58% of pts.
 R0 resection could be achieved in 96% of metabolic
responders
 Event free survival in metab. Responder 29.4mon
compared with 14.1 mon in non responders
Lordick Lancet Onco 2007

12.  All above data does not hold true if pt gets neo
adjuvant chemo-radio
 No difference in pathological response w.r.t. SUV
changes on PET, possibly due to stunning effect of
radiation on cancer cells
 Conclusion - PET is promising modality for chemo
response detection,

13. Role in detection of
recurrence
 A follow-up study of 112 pts. sensitivity for local,
regional and distant recurrences – 50%, 92% and
89.9%
Guo H J Nuc Med 2007
 Another study for loco regional recurrence PET vs CT
sensitivity and specificity 100vs 65% and 85% vs 91%
 PET in this study had 100% predictive value but
reviews(WGJ) say its too early to recommend for
general use.
Teyton J Gastroint Surg 2009

14.  NCCN Guidelines, 2015 –
 PET only for assessment of chemo response before
surgery
 PET should not be used for selection of pts. to surgery
following pre-op chemo-radiation
 Comparison of FDG PET with other molecules like FLT
– fluorothymidine showed that FDG is better than FLT,
thus FLT has no role at present.
van Westreenen J Nuc Med 2006

15. Gastric adenocarcinoma
 Unlike esophageal tumors gastric lesions less well
imaged
 Various series ranging from 21-100% sensitivity
Latest – Kameyama R Eur J Nuc Med 2009
 FDG uptake may also be seen in superficial and erosive
gastritis

16. Role in tumor size and depth
 Sensitivity is lower for size
<3cm – 21%
 T1 lesions less likely to be
detected

17.  Histological sub type variation is also noted
 Non intestinal type – 0-77% sensitivity
 Intestinal type 44- 92% sensitivity
 This variation may be related to variability in GLUT-1
receptor expression
 But variation in histological subtype does not correlate
with SUV
Takahashi Ann Nuc Med 2009

18.  Role in screening- Not effective, sensitivity only 10% compared
to OGDscopy, PPV 8.3%
Shoda H Br J Cancer 2007 similar in other studies
 Lymph node status assessment – Sensitivity is generally low – 22-
60%
Kamimura Nuc Med Commun – 2009
 PET compared with CT, sensitivity of CT 52-77%, specificity 62-94%
vs PET specificity – 62-100%
Yashioka T J Nuc Med 2003
 Role in peritoneal disease assessment - Inferior to CT(sensitivity -
76 -80% vs PET – 9-30%)

19.  Response to preop chemo- Response criteria – 35%↓ in SUV value
of target lesion
 Metabolic response predicted histological response in 10/13 pts.
sensitivity 77% and specificity 86%
Weber W A, J Clin Onco
 Role in prediction of survival - At 2 year follow-up survival in
metabolic responders – 90% vs 25% in nonresponders
Di Fabio gastric cancer 2007

20. Role in detection of
recurrence
 Compared with CT lesser sensitivity(87% vs 47%) but
greater specificity(70-100%)
Sim SH BMC Cancer 2009
 FDG PET utility in recurrence detection is dependent
on prevalence of ca stomach i.e., higher prevalence
a/w higher PPV

21. NCCN guidelines 2015
 PET-CT has higher accuracy in preop staging i.e. 68% than
PT(47%) and CT(53%) alone
 PET alone is not adequate in staging of ca stomach, but it
could be helpful when used in conjunction with CT
 PET/CT is useful in predicting chemo response and
recurrence prediction
 PET may be also be useful in detecting occult mets, but
additional studies needed to establish utility.

22. Pancreatic adenocarcinoma
 Role in diagnosis – Sensitivity 85% for ca pancreas and 84% for
chronic pancreatitis based on SUV cutoff of 4
 PET has lower sensitivity than EUS but higher specificity than all
other modalities
 Sensitivity of PET increases when blood glucose is corrected to
normal levels
Sperti J Gastrointest Surg 2005
 Ability of PET is greater than CT in detecting smaller lesion
Gambhir et al J Nuc Med 2001

23.  Role in staging – Not a preferred modality, due to
poor spatial resolution.
 Lymph node staging – Sensitivity ranges from 49-76%
for local field involvement.
 For hepatic mets - sensitivity of 97% if size >1cm but
specificity <43% if <1cm.
 Role in prognostication - SUV >4.0 overall survival 7
mon, compared to those with 32mon those with SUV
<4.
Sperti J Gastrointestinal surg 2006

24. Role in chemo response
prediction
 Those with 50%↓ SUV from baseline, 10% had
complete surgical resection
 Compared to 6% for those with non respoders
 Those with response had survival 23.2mon vs non
responders survived – 11.3mon
Choi Am J Clin Onc 2010
 PET response correlates with tumor markers fall
Kuwatani Int Med 2009

25. Role in predicting recurrence
 PET is superior in predicting than CT and MRI in
detection of recurrence (96% vs 39%)
 CT and MRI though poor for local recurrence but
sensitive for hepatic mets and better than PET.
 PET is complementary to CT in recurrence
detection(increases sensitivity to 94.7%)
Ruf Pancreatology 2005

26. NCCN guidelines 2015
 Role in staging
PET/CT is not a substitute for high quality CECT but can be
considered adjunct to CT in high risk with mets
 Borderline resectable
 Markedly elevated CA 19.9
 Large primary tumor
 Large regional LN
 Very symptomatic pt.

27. Colorectal cancer
 Value in preop staging – Insufficient evidence for its routine use
 Sensitivity for recurrent disease – 91% and specificity 91%.
Review of 30 studies J Brush Health tech Assess 2011
 Role in colorectal liver mets –PET-CT is better than CT in detecting
extra hepatic mets but at least equal to CT in intrahepatic mets

29.  The studies show that PET may change management in
10-21% of patients i.e. avoidance of surgery
 Response prediction after chemo therapy – PET-CT
predicts tumor response in 70% of lesions vs CT alone.
Goshen E Technol Can Res 2011
 Whom to scan? – consensus in reviews – only if
suspicion of mets high after CT/MRI used after
multidisplinary opinion

30. NCCN guidelines 2015
 Non metastatic ca colon
 No routine use
 Indicated if – inconclusive imaging results on MRI or CT, not useful
for sub centimeter lesions
 Synchronous mets
 Recommended if prior imaging suggest potentially resectable M1
lesion, to identify if any unresectable mets exist
 C/I for clearly unresectable mets on prior imaging
 C/I in chemo response assessment since False –ve for transient
period post chemo/ false +ve - if inflamed, MRI used instead

31. NCCN guidelines 2015
 Metachronous mets –
 Main role in establishing extra hepatic mets if any
 Preop PET changes management in ~25%
 Though no impact on survival, surgical management
changes in nearly 8%
 Surveillance
 Not recommended as routine
 But may be indicated in pts. with high CEA and negative
good quality CECT

32. Hepato-biliary malignancies
 HCC – only 30-50% demonstrate uptake of FDG
Okazumi J Nuc Med 1992
 Alternative tracer – 11C acetate has been used in conjunction with
FDG
 Well differentiated HCC - -ve FDG, +ve C acetate
 Undifferentiated - +ve FDG, -ve for C acetate
 Moderately differentiated mixed affinity
 But applicability of this uptake pattern still in abstracts level
 FDG – reported to be more accurate than CT (90% vs 45%) in
detecting recurrence after TACE or RFA
Zhao, WJG 2005

33. Cholangioca and GB ca.
 Very few studies
 No enough data for comparing efficiency of different
modalities in evaluating PET
 Most individual studies PET is better than other
imaging in detecting mets, regional LNs.
 PET - Poor intrahepatic mets detection vs better extra
hepatic detection

34.  NCCN for cholangio ca. – though not established PET may be used in
assessment regional LN and potentially resectable disease for finding
distant mets

35. Neuroendocrine tumours
 Different radio tracers may be needed because of
histological composition
 Overall data shows that PET is more accurate and
sensitive than CT alone or MRI.
Kayani Nuc Med Jour 2008
 Intrahepatic mets lesser accuracy than other modalities
 May add to diagnostic yield when used as adjunct to
other modalities

36. Thank You
 They said I will need a “PET” scan