44. Comparison between thallium-201 and Tc-99m mibi uptake in patients with brain tumors

SPET with thallium-201 ( ²⁰¹T1) is used in the assessment of brain tumors because the amount of ²⁰¹T1 accumulated by the tumor cells is proportional to the degree of tumor malignancy, thus making it possible to differentiate high-grade from low-grade gliomas or recurrence from radiation necrosis. Tc ^99m sestamibi has been more recently used to study brain tumors. It offers the advantages of Tc ⁹⁹m labeled molecules including daily availability, good image contrast, low cost and short biological half-life. We studied 20 patients (9 m and 11 f, mean age: 51.3 ± 18 yrs) with histologically proven supratentorial brain tumors (low grade glioma = 4; high grade glioma = 7; radiation necrosis = 2; lymphoma = 1; meningioma = 3; metastasis = 2; histiocytosis = 1) with both the radiotracers (3 mCi of ²⁰¹Tl and 20 mCi of Tc ^99m sestamibi) in the same SPET session (Tomomatic 564, Medimatic; Denmark). All patients underwent MRI or CT scan shortly before the SPET study. The ²⁰¹Tl and Tc ^99m sestamibi uptake were calculated as the ratio between the average counts in a region of interest (ROI) of the tumor and the average counts in a symmetrical ROI in the unaffected hemisphere ( ²⁰¹Tl and Tc ^99m sestamibi indices). The tumor ROI was chosen on the slice showing the maximal tracer uptake. This ROI included all the tissue with tracer uptake higher than 50% of the maximum activity. The Tc ^99m sestamibi index was significantly higher than the ²⁰¹Tl index (2.8 ± 1.3 vs 2.3 ± .86, P =.02 t-paired test). A significant correlation was observed between ²⁰¹Tl Index and Tc ^99m sestamibi indices (y = 1.109x + .244; r = .736, p <.0002). These findings indicate that Tc ^99m sestamibi has biological properties in brain tumors similar to those of ²⁰¹Tl. Its practical advantages encourage a wider clinical application in the study of cerebral neoplasms.