3-[I-123]IODO-ALPHA-METHYLTYROSINE AND [METHYL-C-11]-L-METHIONINE UPTAKE IN CEREBRAL GLIOMAS - A COMPARATIVE-STUDY USING SPECT AND PET

This study compares the uptake of the nonmetabolizable amino acid anal og 3-[I-123]iodo-alpha-methyltyrosine (IMT) and of [methyl-C-11]-L-met hionine (MET) in cerebral gliomas. Methods: In 14 patients with cerebr al gliomas, IMT uptake was measured using SPECT (10 dynamic, 4 static SPECT acquisitions) and, on the same day, MET uptake by dynamic PET. T he IMT and MET data were compared with respect to tracer kinetics, tum or to brain ratios (T/B) and tumor size after converting the resolutio n of the PET scans to that of the SPECT scans (14 mm FWHM). Results: A ll gliomas showed increased uptake of both tracers in relation to norm al brain tissue. Visual comparison of the scans yielded no differences in tumor size and shape with both methods. IMT showed a maximal trace r uptake in brain and in tumors at about 15 min postinjection which wa s followed by a washout of 45.0% +/- 13.5% in gliomas (mean +/- s.d., p < 0.001, n = 10)and 35.3% +/- 5.4% in normal brain (p < 0.001, n = 1 0) at 60 min postinjection. MET concentration in tumor tissue or brain tissue between 15 and 60 min remained constant. T/B ratios of IMT SPE CT and MET PET showed a significant correlation at 15 min postinjectio n (r = 0.69, n = 10, p = 0.03), a low correlation for the mean values of the scans from 15-60 min postinjection (r = 0.54, n = 14, p = 0.05) and no correlation at 60 min postinjection (r = 0.09, n = 10, n.s.). Conclusion: IMT and MET uptake in gliomas is similar in the early, tra nsport dominated phase. There are some differences in tumor to brain r atios between both tracers within the first hour postinjection that ar e mainly caused by variable washout of IMT. Imaging of tumor extent wi th IMT SPECT is comparable to MET PET. Thus, amino acid SPECT using IM T is a promising tool to evaluate the biological activity and intracer ebral infiltration of gliomas.