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).