Abstract
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Purpose: For patients with pancreatic cancer, surgical resection remains the only curative modality. Neo-adjuvant therapy (NAT) can potentially reduce tumor volume & treat early micro-metastatic disease, thereby increasing the likelihood of surgical resection with negative margins. However there are currently no reliable biomarkers to evaluate and guide NAT. The purpose of our study is to determine if FDG PET/MRI can be used to predict pathologic treatment response in FDG-avid borderline resectable pancreatic ductal adenocarcinoma (PDAC) after neoadjuvant therapy. Materials and Methods: This is an IRB-approved, HIPAA-compliant retrospective study. Our institutional PET/MRI database (04/2016-06/2017) included 105 patients with pancreatic cancer who underwent FDG PET/MR on a 3.0 T time-of-flight PET/MRI (SIGNATM, GE Healthcare). Inclusion criteria included patients with FDG-avid PDAC on baseline (pre-NAT) PET/MRI, NAT, a post-NAT PET/MRI and subsequent surgical resection. Final study cohort comprised of 12 patients. Imaging protocol consisted of multi-bed position whole body survey (2-4 minutes/bed) with an additional 15-minute single bed position respiratory-compensated focused abdominal PET. MR sequences included respiratory-navigated T2W, DWI, IDEAL-IQ, MRCP and breath-hold post-contrast dynamic sequences (average protocol duration ~ 60-minutes). Primary tumor SUVmax, SUVmean and volumetric PET parameters on pre- and post-NAT scans were measured using anatomic guidance from simultaneously acquired contrast-enhanced MRI. Metabolic response on PET/MRI was correlated to histologic treatment response using the College of American Pathologists grading system (pathology response grade, 0-3). Complete metabolic response defined as FDG uptake indistinguishable from surrounding background and normalization of post-therapy CA 19-9 were evaluated as surrogates of pathology response grade 1/0.
Results: Mean age at presentation was 67.1 (range 55-78years; 50% males). Treatment response grades were none (grade 3, n=2), moderate (grade 2, n=6), marked (grade 1, n=2) and complete pathologic response (pCR) (grade 0, n=2). There was no significant difference (p > 0.05) in baseline PET parameters between group 1 (grade 3/2) and group 2 (grade 1/0). Complete metabolic response on post-therapy PET/MRI was observed in 5 patients - one with grade 2, and two each with grades 1 and 0. The positive and negative predictive values of PET/MRI for complete metabolic response (for pathology response grade 1/0) were 80% and 100% while those for normalization of post-therapy CA 19-9 were only 20% and 33%, respectively. Conclusions: FDG PET/MRI shows promise for response evaluation following NAT with complete metabolic response by PET/MRI correlating with marked or complete pathologic response.
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