RESUMEN
Recurrent glioma in patients who are symptomatic after high dose of radiotherapy is difficult to differentiate from radiation necrosis by conventional imaging techniques [CT] scan and MR imaging. Thailuim-201 SPECT is useful in prediction the viable tumour cells in patients with glioma. To clarify the usefuillness of TL-201 SPECT in differentiating the tumour recurrence from radiation necrosis and to evaluate the relationship between tumour perfusion and early TL-201 uptake. Thirty-six patients [age ranged from 16 to 65 years old 26 males and 10 females] deteriorated clinically after high dose of radiation therapy. CT scan or MR imaging performed in all patients, but failed to differentiate between the recurrence of tumour and radiation necrosis 111 MBQ of Thallium-201 were injected and first minute perfusion, early [15 minutes post injection] and late [3 hours post injection] SPECT images were acquired. The results were assessed by both visual [semi quantitative] and Quantitative evaluation. We found a sensitivity, specificity and accuracy of 97.2% 93.2 and 94.4% respectively for visual evaluation. And for the quantitative evaluation the sensitivity, specificity and accuracy were 100%, 94.4% and 97.2% respective. The mean Thallium-201index [T1] and retention index [R1] for recurrent gliomas were 2.6 and 2.0 for both early and delayed Scans respectively: while in radiation necrosis the indices were [1.1 +/- SD 0.1] in early scans and [1.1 +/- SD0] for delayed scans. Two patients in our study had a contradictory results; one had a recurrent glioma with TL-201 index [T1] 1.8 and retention index [R1] 13% [false negative] while the other patient diagnosed pathologically as radiation necrosis and had a T1 and R1 of 2.7 and 18,5% respectively [false positive]. The mean retention indices for both recurrence and radiation necrosis in our study were 21% and 8.7% respectively. Also we found a poor correlation between perfusion and early TL-201 uptake in the study group [rho= 0.41]. The quantitative 201 TL SPECT is a useful noninvasive tool for differentiating recurrent glioma from post radiation necrosis