Usefulness of thallium-201 SPECT for prediction of early progression in low-grade astrocytomas diagnosed by stereotactic biopsy

Objective: To establish the value of thallium-201 single-photon emission computed tomography (²⁰¹Tl-SPECT) as a predictor of early progression in low-grade astrocytomas (LGAs). Methods: We studied 57 consecutive patients who underwent 201 Tl-SPECT before stereotactic biopsy (n = 33) or surgical resection (n = 24). The value of radiologic and histopathological variables (²⁰¹Tl index and MIB-1 index) in predicting progression free survival (PFS) was examined in each group of patients. Results: During a median follow up of 55 months (range, 11-101), progression of the primary lesion was identified in 46 patients (80.7%). Based on Cox's proportional hazards model, the increased thallium uptake was associated with a short PFS in both biopsy and resection groups, whereas the MIB-1 index was significant only in the resection group. Considering the cut-off value, ²⁰¹Tl index > 1.7 was statistically significant for reduced PFS in the biopsy group; however, MIB-1 index was not directly related to the PFS at any level. For the surgical resection group, both a ²⁰¹Tl index > 1.9 and a MIB-1 index > 6% were associated with short PFS. Conclusion: ²⁰¹Tl SPECT may play a role in prediction of early tumor progression not only in resected LGAs, but also in biopsy-proven LGAs. Therefore, we suggest that patients with LGAs established from biopsy should be considered as high-risk groups for early progression if the tumor shows a high ²⁰¹Tl uptake, even if the tumor demonstrates low proliferative activity on histopathologic examination.