18F-Fluciclovine PET/CT in the Assessment of Pancreatic Transplants

Overview

Hypothesis 1: 18F-Fluciclovine PET/CT can correctly and easily identify the pancreatic allograft and determine its viability Aim 1: Assess whether 18F-Fluciclovine can identify the pancreatic allograft accurately and assess its viability and visibility Hypothesis 2: 18F-Fluciclovine PET/CT uptake in the pancreas (SUV) is related to total pancreatic function and therefore can indicate whether the pancreatic allograft is at risk of rejection Aim 2: Assess whether 18F-Fluciclovine uptake in the pancreas can be a surrogate for pancreatic function

18F-Fluciclovine is a synthetic L-leucine amino acid used clinically for PET imaging in patients with biochemical recurrence of prostate cancer following definitive therapy. The pancreas accumulates striking amounts of Axumin, where it is considered a normal finding. Pancreatic beta-cell function may be slow to recover following pancreatic transplantation and may vary as a function of perioperative steroid administration, acute rejection, inadequate islet cell transplantation, allograft pancreatitis or compromised blood supply. The viability of the allograft is a common clinical concern and is difficult to assess based on insulin, C-peptide, and blood sugar levels. Rapid identification of compromised allograft viability is critical in the management of these patients. Pancreas transplants are usually assessed via ultrasound as a first-line modality. However, visualization is largely obscured due to the intraperitoneal location of the transplant. There is often overlying gas and due to the depth of the transplant, there is poor visualization with ultrasound. Additionally, the transplant lacks a capsule which results in its being ill-defined and difficult to distinguish from adjacent structures. Computed tomography can also be used to assess pancreas transplants, however, most transplant patients often have concurrent renal transplants which limits the use of intravenous iodinated contrast. On non-contrast CT, it can be difficult to assess and distinguish the pancreas transplant from the adjacent bowel. Magnetic Resonance Imaging (MRI) can be useful and has better soft-tissue contrast compared to CT. However, it has a similar issue with regards to limited intravenous gadolinium contrast administration due to concurrent renal transplant in this group of patients. In all three modalities, there is no functional assessment of the allograft and whether there is still appropriate pancreatic function. This is the reason for our proposed study, given that 18F-Fluciclovine is readily taken up by the pancreas and it would help radiologists readily identify where the allograft is located, whether it is viable, and whether there is a normal function of the allograft. It should be noted that leucine serves both as a fuel, as well as in a regulatory capacity for pancreatic beta-cell function. However, uptake of 18F-Fluciclovine in the pancreas is not likely to be specific for beta-cell function since acinar cell function requires L-amino acids. However, overall pancreatic viability is relevant to both acinar cell and beta-cell function.