First experience with I-123-alpha-methyl-tyrosine SPECT in the 3-D radiation treatment planning of brain gliomas

Purpose: This study compares the results of iodine-123-alpha-methyl-tyrosin e single photon computed emission tomography (IMT-SPECT) with magnetic reso nance imaging (MRI) in tumor volume definition of brain gliomas. Furthermor e, it evaluates the influences of the information provided from IMT-SPECT f or three-dimensional (3D) conformal treatment planning. Methods and Materials: In 30 patients with nonresected, histologically prov en brain gliomas (glioblastoma-13 patients, astrocytoma Grade III-12 patien ts, astrocytoma Grade II-3 patients, oligodendroglioma Grade III-1 patient, oligodendroglioma Grade II-1 patient), IMT-SPECT and MRI were performed pr etherapeutically in the same week. A special software system allowed the co registration of the IMT-SPECT and MRI data. The gross tumor volume (GTV) de fined on the IMT-SPECT/T2-MRI fusion images (GTV-IMT/T2) was compared with the GTV-T2, defined on the T2-MRI alone. On the IMT-SPECT/T1Gd-MRI overlays , the volume of the IMT tumor uptake (GTV-IMT) was compared with the volume of the gadolinium (Gd) enhancement (GTV-T1Gd). The initial planning target volume (PTV) and the boost volume (BV) outlined on the IMT-SPECT/T2-MRI co -images were analyzed comparatively to the PTV and BV delineated using the T2-MRI alone. Results: In all 30 patients a higher IMT uptake of tumor areas, compared to the normal brain tissue was observed. Mean GTV-IMT, mean GTV-T2, and mean GTV-T1Gd were 43, 82, and 16 cm(3), respectively. IMT tumor uptake outside the contrast enhancement regions was observed in all patients. Mean relativ e increase of tumor volume defined on the fusion images, GTV-IMT/T1Gd versu s GTV-T1Gd alone was 78%. IMT tumor uptake areas outside the GTV-T2 were re gistered in 7 patients (23%). In these patients, the mean increase GTV-IMT/ T2 was 33% higher than GTV-T2, defined according to the T2-MRI data alone. The additional information provided by IMT-SPECT modified minimally the ini tial PTV (mean relative increase PTV-IMT/T2 versus PTV-T2, 5%) but signific antly the BV (mean relative increase BV-IMT/T2 versus BV-T2, 37%). Conclusion: In a significant number of patients, the IMT-SPECT investigatio n improves tumor detection and delineation in the planning process. This ha s important consequences in the 3D conformal treatment planning, especially in the delineation of BV and in dose escalation studies. (C) 2000 Elsevier Science Inc.