Measurement of Functional Tumor Volume in Patients with Pancreatic Cancer using 18F-FLT and 18F-FDG PET/CT

INTRODUCTION: This phase-I imaging study examined the imaging characteristic of 3’-deoxy-3’-(18F)fluorothymidine (18F-FLT) positron emission tomography (PET) in patients with pancreatic cancer and comparisons were made with (18F)fluorodeoxyglucose (18F-FDG). The ultimate aim is to develop a molecular imaging tool that could better define the biologic characteristics of pancreas cancer, and to identify the patients who could potentially benefit from surgical resection who were deemed inoperable by conventional means of staging.
METHODS: Six patients with newly diagnosed pancreatic cancer underwent a combined FLT and FDG PET/CT imaging protocol. The FLT PET/CT scan was performed within 1 week of FDG PET/CT imaging. Tumor uptake of a tracer was determined and compared using various techniques: statistical thresholding (Z-score =2.5), and fixed standardized uptake value (SUV) thresholds of 1.4 and 2.5, and applying a threshold of 40% of maximum SUV (SUVmax) and mean SUV (SUVmean). The correlation of functional tumor volumes (FTV) between 18F-FDG and 18F-FLT was assessed using linear regression analysis.
RESULTS: It was found that there is a correlation in functional tumor volumes due to metabolic and proliferation activity when using a threshold of SUV 2.5 for FDG and 1.4 for FLT (r = 0.9606, p < 0.05), but a better correlation was obtained when using SUV of 2.5 for both tracers (r = 0.973, p<0.05). The Z score thresholding (Z =2.5) method showed lower correlation between the FTVs (r=0.698, p-value = ns) of FDG and FLT PET.
DISCUSSION AND CONCLUSION: Different tumor segmentation techniques yielded varying degree of correlation in functional tumor values between FLT and FDG-PET images.