99mTc-GHA Brain SPECT in the evaluation of brain tumors

Abstract

1549 Background: Brain tumors are of diverse histological types, the most common being from glial tissue. The clinical management and prognosis of brain tumor patients is dependent on accurate neuro-pathologic diagnosis and grading. CT scan though provides accurate information about location of the tumor. MRI may be helpful in classifying the grade of tumor. Radionuclide imaging techniques using of Tl-201 SPECT and 18F-FDG PET studies have been widely reported to evaluate malignant lesions. 99mTc-GHA (Glucoheptonate), more or less analogous to 18F-FDG, may show increased glucose metabolism and help in grading tumors. Methods: We studied 29 patients (17 M, 12 F) aged 13–60 years (35.7 ± 12.4) of brain tumors by Tc99m-GHA Brain SPECT, performed 40 min and 3 hours after radiotracer administration. Reconstruction of the SPECT data was done using standard software. Abnormal concentration of tracer at the tumor site was compared to normal uptake on the contralateral side, and ratios obtained for early (40 min) and delayed (3 hours) uptake of tracer. Retention ratio (RR), was then calculated, and compared with the final histological diagnosis. Results: Of the 29 patients studied, 13 were histologically low-grade [WHO grade] tumors while 16 were high-grade tumors. On scintigraphy, no tracer uptake was noticed in 5, very low uptake in 8, moderate uptake in 6 and very high uptake in 10. RR of all the tumors ranged from 0.72 - 1.39. Low-grade gliomas (grade II) showed a lower RR (0.72 - 0.97) (mean 0.85 ± 0.10), while high-grade gliomas (grade III/IV) had a higher RR (1.03 - 1.29) (mean 1.11 ± 0.07). On histopathological correlation, it was found that the RR at a threshold of 1.0 yielded the maximum accuracy for discriminating between low (grade I/II) and high-grade (III/IV) gliomas. This corresponded to a sensitivity of 90%, a specificity of 55.5% and an overall predictivity of 82.6% of 99mTc-GHA SPECT imaging for grading of cerebral gliomas. Conclusions: This study suggests that Tc99m-GHA SPECT with early and delayed imaging is a good indicator of brain tumor activity and may prove to be an economical and efficient technique for grading of glial tumors of the brain. It may further be hypothesized that Tc99m-GHA demonstrates the actual metabolic activity of these tumors. No significant financial relationships to disclose.