PET scan in gi malignancy
- 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