Positron emission tomography using 18F-fluorodeoxyglucose in patients with stereotactically irradiated brain metastases.

Thirty-one patients with intracranial metastases were examined with positron emission tomography (PET) using 18F-fluorodeoxyglucose (FDG) as a tracer. The PET study was prompted by growth of the tumor in spite of therapy, or regrowth after an initially favorable response. Increased accumulation of FDG was seen in 14 patients (group 1) and decreased in 17 (group 2). Patients in group 1 had verified tumor growth in 9 of 14 cases. The median survival after radiosurgery was 12.3 months. One patient in this group is still alive after open surgery of a recurrent metastasis. Six patients in group 2 are still alive. The median survival after radiosurgery was 19.9 months. Verified radiation reaction/necrosis was found in 5/17 and viable tumor tissue in 2. The survival time in group 2 was significantly longer than in group 1. PET is superior to computed tomography and magnetic resonance imaging in the differentiation between recurrence and radiation reaction/necrosis. However, temporary radiation effects may mask remaining tumor tissue, and repeat PET studies may sometimes be necessary.

Recurrent tumor vs radiation effects after gamma knife radiosurgery of intracerebral metastases: diagnosis with PET-FDG.

OBJECTIVE: Our objective was to differentiate radiation effects from tumor progression in metastases stereotaxically irradiated with the multi-cobalt unit (Gamma Knife). MATERIALS AND METHODS: Eleven patients with stereotaxically irradiated cerebral metastases were examined with PET using [18F]fluorodeoxyglucose (FDG) to differentiate recurrent tumor from radiation effects. RESULTS: Six patients had increased uptake of FDG, and clinical, radiological, and pathological findings confirmed the diagnosis of recurrent metastases. These patients had an unfavorable prognosis and were all dead within 54 weeks after radiosurgery. Five patients had lesions without an increased accumulation of FDG. Four of these patients were alive after a total follow-up of 1.7 years, while one patient died of a peptic ulcer 56 weeks after radiosurgery. CONCLUSION: Positron emission tomography with FDG was of obvious prognostic value in this small series of patients and was clearly superior to CT and MR in the distinction between tumor recurrence and radiation effects (verified necrosis in one case).