Evaluation of the extension of cerebral gliomas by scintigraphy

Background: Single photon emission computed tomography (SPECT) with Tl-201 and I-123-alpha-methyl tyrosine (I-123-IMT) are routine methods for the eva luation of brain tumors. I-123-IMT transport across the blood brain barrier is mediated by an amino acid carrier, Tl-201 accumulation is analogous to cerebral potassium uptake. Patients and Methods: To determine the differences in glioma extension as s hown by the 2 methods, 17 patients with malignant gliomas were included in this comparative imaging study: astrocytoma III: n = 6, ependymoma III: n = 1, oligodendroglioma III: n = 1, glioblastoma IV: n = 9. The tomographic i mage sets were matched anatomically and the slices showing maximal tumor ex tension were identified in both image sets respectively. Tumor spread was c ompared visually and the tumor extension was quantified. Results: In gliomas WHO III tumor extension was delineated significantly la rger by I-123-IMT-SPECT than by Tl-201-SPECT (mean +/- SD: 816 +/- 281 pixe ls vs 600 +/- 220 pixels, n = 8, p < 0.05). The size of glioblastomas was s hown in a comparable manner by the 2 methods (977 +/- 571 vs 1.051 +/- 588, n = 9, ns, p = 0.57, but there were considerable regional differences betw een the area of Tl-201 uptake and amino acid retention, in the whole group a weak but significant negative correlation between intensity of Tl-201 upt ake on the one hand and a ratio of the area as depicted by I-123-IMT vs are a as depicted by Tl-201 on the other hand, was found (n = 17, r = 0.49, p < 0.05), Thus the differences in the delineation of areas became smaller wit h increasing Tl-201 uptake. Conclusions: These preliminary data indicate that the extension of gliomas is depicted differently by the 2 methods. IMT-SPECT shows a larger tumor ex tension especially in gliomas WHO III. Since Tl-201 uptake has previously b een shown to correlate with disruption of the blood brain barrier, I-123-IM T-SPECT may delineate tumor parts without endothelial leakage. This additio nal information may be helpful in planning surgical or radiation therapy. T he advantages of I-123-IMT in this respect decrease with increasing Tl-201 uptake and with increasing malignancy.