Visual and semi-quantitative assessment of brain tumors using 201Tl-SPECT

Objective : To evaluate the usefulness of 201Tl-SPECT in differentiating benign from malignant brain tumors. Methods and Materials : Eighty-eight patients (44 males and 44 females) with 58 high-grade (WHO grade III-IV) and 30 low-grade (WHO grade III) tumors were evaluated with 201Tl-SPECT. (1) Visual assessment was performed by board-certificated radiologists using 201Tl-SPECT. Tumors were classified in two groups (Tl-positive and Tl-negative) and scored using the five grade evaluation system. Receiver operating characteristic (ROC) analysis was performed in the Tl-positive group. (2) Semi-quantitative assessment involved measurement of early and delayed 201Tl uptake, and the retention index (RI) was applied as follows : RI=delayed uptake ratio/early uptake ratio. Three combinations of RI using mean and maximum values of the region of interest were calculated. Results : (1) Seventy-four Tl-positive and 14 Tl-negative tumors. The area under the ROC curve (AUC) estimated by three radiologists exceeded a value of 0.7. The value was greater when estimated by the more experienced radiologist. (2) In all RIs, the difference of RI between high-grade tumors and low-grade tumors was statistically significant. Conclusion : A visual and semi-quantitative assessment using 201Tl-SPECT was found to be useful for differentiating benign from malignant brain tumors.