pet scan in gi malignancy
TRANSCRIPT
Positron Emission Tomography in Gastrointestinal malignancies
SHANKAR ZANWAR
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 ƴ rays at diametrically opp. direction that are detected & localized detector gantry.
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.
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
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
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
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
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
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
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
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
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,
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
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
Gastric adenocarcinoma
Unlike esophageal tumors gastric lesions less well imaged
Various series ranging from 21-100% sensitivityLatest – Kameyama R Eur J Nuc Med
2009
FDG uptake may also be seen in superficial and erosive gastritis
Role in tumor size and depth
Sensitivity is lower for size <3cm – 21%
T1 lesions less likely to be detected
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
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%)
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
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
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.
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
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
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 fallKuwatani Int Med 2009
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
NCCN guidelines 2015
Role in stagingPET/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.
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
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
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
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
Hepato-biliary malignancies
HCC – only 30-50% demonstrate uptake of FDGOkazumi 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
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
NCCN for cholangio ca. – though not established PET may be used in assessment regional LN and potentially resectable disease for finding distant mets
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
Thank You
They said I will need a “PET” scan