Differential diagnosis between recurrence of brain tumor and radiation necrosis by 201Tl SPECT

In order to differentiate recurrence of brain tumor from radiation necrosis, we performed 201Tl brain SPECT in 16 post-operative patients. Five of them had residual anaplastic astrocytoma. Final diagnosis of the other 11 patients was recurrent astrocytoma (n=6), cerebral radiation necrosis (n=5), based on re-operation (n=9) and more than one year follow-up findings (n=2). Early and delayed images were obtained at 10∼15 min. and 4 hrs. after i.v. injection of 111 MBq of 201Tl chroride. Counts ratio of a lesion to the normal brain (L/N) was calculated by creating rectangular ROI over each area. All of the patients with recurrent or residual tumor showed L/N ratios of more than 2.5 on the early images (mean 4.70 ± 2.65). On the other hand, L/N ratios on the early images were less than 2.5 in patients with radiation necrosis (mean 2.05 ± 0.25, p<0.001). In conclusion, a quantitative assessment using 201Tl brain SPECT may be useful in differentiating recurrence of brain tumor from radiation necrosis. (author)