PROTON MR SPECTROSCOPY OF DELAYED CEREBRAL RADIATION IN MONKEYS AND HUMANS AFTER BRACHYTHERAPY

PURPOSE: To determine whether radiation necrosis can be differentiated from residual/recurrent tumor by proton MR spectroscopy. METHODS: We studied the effects of interstitial brachytherapy on the brains of hea lthy monkeys and in humans with glioblastoma multiforme. The effects o f radiation therapy on normal brain tissue in monkeys were assessed wi th sequential proton MR spectroscopic studies 1 week to 6 months after brachytherapy. Proton MR spectroscopy was also performed in five pati ents with residual/recurrent glioblastoma multiforme (three of whom ha d radiation necrosis after brachytherapy), seven patients with newly d iagnosed untreated glioblastoma multiforme, and 16 healthy volunteers, who served as a control group. RESULTS: In monkeys, the ratio of N-ac etylaspartate (NAA) to creatine-phosphocreatine (Cr) and the ratio of choline-containing compounds (Cho) to Cr of the reference point were s ignificantly lower 1 week after brachytherapy than before treatment. T he ratio of NAA to Cho of the irradiated area tended to be higher 1 we ek after brachytherapy than before irradiation. These peak metabolic r atios showed characteristic changes 6 months after treatment. In two o f three monkeys, lipid signal was elevated 6 months after irradiation. In the clinical study, the ratio of NAA to Cho in the area of radiati on necrosis was significantly different from that in glioblastoma mult iforme when compared with the contralateral hemisphere after irradiati on. In addition, lipid signal was detected in all patients with radiat ion necrosis. CONCLUSION: It might be possible to use proton MR spectr oscopy to differentiate radiation necrosis from residual/recurrent gli oblastoma multiforme on the basis of comparisons with the contralatera l hemisphere after radiation therapy.