Spatial and temporal variability of intratumoral 18F-FDG distribution in patients with cancer.
e21149 Background: We previously reported that in mice models, tumor microenvironment is complex and intratumoral 18F-FDG distribution is heterogeneous. There were apparent spatial and temporal intratumoral 18F-FDG distribution changes occurring even within 24-48 hour interval in human cancer cell xenografts grown in nude mice. We hypothesized that what was documented in mice models may also be applicable to human patients with cancer. The objective of this study was to investigate the intratumoral spatial and temporal distribution of 18F-FDG in cancer patients. Methods: Five patients who had repeat PET/CT scans within 1-28 days and with no interval therapy were identified. All patients had fasted overnight and had blood glucose level of less than 200 mg/dl. They were injected with 8.0-14.0mCi of 18F-FDG intravenously, and whole body PET/CT scans were performed 60-80 minutes later utilizing a Siemens PET/CT scanner. Each patient’s intratumoral FDG activity distributions were mapped and compared to each other utilizing magnified digital images of the tumors. Results: Intratumoral FDG activity is very heterogeneous. Within the same tumor, there is a wide range of high and low FDG uptake variations. Apparent change in intratumoral FDG distribution was found within as short as a 24 hour interval in the same patient. Although the global tumoral FDG activity and liver FDG activity measured as SUVmaximum and SUVaverage were not significantly different from one PET/CT to another, there were significant spatial changes and variations of the tumor FDG activity between the two PET/CT images. Conclusions: Intratumoral 18F-FDG uptake is very heterogeneous and manifests both temporal and spatial changes within as short as 24 hours even in untreated cancer patients. This should be taken into consideration during FDG PET based therapy decisions, for example in tumor and nodal staging or radiation therapy planning.