Interest of Integrated Whole-Body PET/MR Imaging in Gastroenteropancreatic Neuroendocrine Neoplasms: A Retro-Prospective Study

Abstract

Introduction and aim: Simultaneous positron emission tomography/magnetic resonance imaging (PET-MRI) combines the high sensitivity of PET with the high specificity of MRI and is a tool for the assessment of gastroenteropancreatic neuroendocrine neoplasms (G-NENs). However, it remains poorly evaluated with no clear recommendations in current guidelines. Thus, we evaluated the prognostic impact of PET-MRI in G-NEN patients.

Methods: From June 2017 to December 2021, 71 G-NEN patients underwent whole-body PET-MRI for staging and/or follow-up purposes. A whole-body emission scan with ¹⁸F-6-fluoro-L-dihydroxyphenylalanine (¹⁸FDOPA, n = 30), ¹⁸F-fluoro-2-deoxy-D-glucose (¹⁸FDG, n = 21), or ⁶⁸Ga-(DOTA(0)-Phe(1)-Tyr(3))-octreotide (⁶⁸Ga-DOTATOC, n = 20) with the simultaneous acquisition of a T1-Dixon sequence and diffusion-weighed imaging (DWI), followed by a dedicated step of MRI sequences with a Gadolinium contrast was performed. The patients underwent PET-MRI every 6-12 months during the follow-up period until death. Over this period, 50 patients with two or more PET-MRI were evaluated.

Results: The mean age was 61 [extremes, 31-92] years. At the baseline, PET-MRI provided new information in 12 cases (17%) as compared to conventional imaging: there were more metastases in eight, an undescribed location (myocardia) in two, and an unknown primary location in two cases. G grading at the baseline influenced overall survival. During the follow-up (7-381 months, mean 194), clinical and therapy managements were influenced by PET-MRI in three (6%) patients due to new metastases findings when neither overall, nor disease-free survivals in these two subgroups (n = 12 vs. n = 59), were different.

Conclusion: Our study suggests that using PET/MRI with the appropriate radiotracer improves the diagnostic performance with no benefit on survival. Further studies are warranted to evaluate the cost-effectiveness of this procedure.

Keywords: G-NET; MRI; PET; PET-MRI; endocrine; gastrointestinal; pancreas.

Figure 1

Study flow diagram. MEN1, multiple endocrine neoplasia of type 1; NF1, neurofibromatosis of type 1. Sporadic designs any G-NEN except those associated with a germline mutation (i.e. Multiple endocrine neoplasia—MEN—or Neurofibromatosis NF1).

Figure 2

(A) Intense 18F-FDOPA avidity revealing primary ileal tumor in metastatic NET with previously unknown primary site. (B) Myocardial metastasis of NET. Intense 18F-FDOPA avidity (middle) and hypersignal in diffusion image (right).

Figure 3

Overall survival. Overall survival (red area represents 95% confidence interval) (A). Survival according to G-NEN location (B), histologic grading (C), and impact of PET/MRI designed as gain or not gain at baseline (D). Survival was compared between groups using log-rank test, p value is as depicted on figures per.