SERIAL PROTON MAGNETIC-RESONANCE SPECTROSCOPY IMAGING OF GLIOBLASTOMA-MULTIFORME AFTER BRACHYTHERAPY

The utility of three-dimensional (3-D) proton magnetic resonance spect roscopy (H-1-MRS) imaging for detecting metabolic changes after brain tumor therapy was assessed in a serial study of 58 total examinations of 12 patients with glioblastoma multiforme (GBM) who received brachyt herapy. Individual proton spectra from the 3-D array of spectra encomp assing the lesion showed dramatic differences in spectral patterns ind icative of radiation necrosis, recurrent or residual tumor, or normal brain. The H-1-MRS imaging data demonstrated significant differences b etween suspected residual or recurrent tumor and contrast-enhancing ra diation-induced necrosis. Regions of abnormally high choline (Cho) lev els, consistent with viable tumor, were detected beyond the regions of contrast enhancement for all 12 gliomas. Changes in the serial H-1-MR S imaging data were observed, reflecting an altered metabolism followi ng treatment. These changes included the significant reduction in Cho levels after therapy, indicating the transformation of tumor to necrot ic tissue. For patients who demonstrated subsequent clinical progressi on, an increase in Cho levels was observed in regions that previously appeared either normal or necrotic. Several patients showed regional v ariations in response to brachytherapy as evaluated by H-1-MRS imaging . This study demonstrates the potential of noninvasive 3-D H-1-MRS ima ging to discriminate between the formation of contrast-enhancing radia tion necrosis and residual or recurrent tumor following brachytherapy. This modality may also allow better definition of tumor extent prior to brachytherapy by detecting the presence of abnormal metabolite leve ls in nonenhancing regions of solid tumor.