A Dual Time Point FDG-PET to Differentiate Between Recurrent Brain Tumor and Radionecrosis

Molecular imaging has been used to distinguish recurrent tumor from post-treatment changes through the use of positron emission tomography (PET) as well as other techniques. The best-studied PET radiotracer for this application is [18F]-fluorodeoxyglucose (FDG). Normal brain matter is very FDG-avid, making it more difficult to identify lesions and in addition, inflammation associated with radiation injury has been shown to be FDG avid.

In light of this, variations of the standard FDG protocols have been proposed in order to increase overall accuracy, including dual time point imaging (DTPI), consisting of injecting the patient with the standard radiotracer and acquiring two sets of images several hours apart, typically the normal initial images in addition to a delayed acquisition set.

There is good reason to suspect that DTPI FDG-PET would be useful a technique for characterizing lesions in the brain. It's been shown that FDG uptake by normal brain parenchyma initially increases then decreases with time, while tumor uptake typically increases and then plateaus. This pattern of increasing and then decreasing FDG activity has also been seen in inflammatory tissue. The difference in FDG uptake at different times is what allows for a better distinction between malignant and benign tissue.