[F-18] Fluorothymidine (FLT) Imaging on Patients With Primary Brain Tumors

Despite significant advances in the understanding of brain tumor biology and genetics as well as improvements in surgical techniques, radiotherapy administration, and chemotherapy methods, many primary brain tumors remain incurable. Most primary brain tumors are highly infiltrative neoplasms, and are therefore unlikely to be cured by local treatments such as surgery, focal radiotherapy, radiosurgery or brachytherapy. A particularly problematic aspect of the management of patients with brain tumors is the eventual development of enhancing lesions on MRI after radiation therapy. The treating physician is then left with the dilemma of what this enhancing lesion may represent (radiation necrosis versus recurrent tumor). The differential diagnosis is between recurrent tumor or radiation necrosis however the amount of each contributing to the enhancing mass on MRI is difficult if not impossible to assess. This particular problem is very common and most patients develop some degree of radiation necrosis after therapy with radiation. Differentiation of necrosis from recurrence is particularly challenging. MRI is typically unable to make this important distinction as there is simply an enhancing mass, the etiology of which could be either necrosis or recurrence. Other imaging methods such as FDG-PET have been used but this technique is also complicated in that the normal brain has FDG uptake and it is often difficult to differentiate recurrence from necrosis. \[F-18\]FLT may prove to be the most reliable method in making this important differentiation (necrosis versus recurrence) as normal brain and necrotic brain do not have proliferative activity and thus no \[F-18\]FLT uptake whereas tumor will have proliferative activity and thus \[F-18\]FLT uptake.