[Differential diagnosis between recurrence of gliomas and radiation necrosis by 201TlCl SPECT]

We studied the value of quantitative 201Thallium Chloride brain SPECT (Tl SPECT) in the differentiation between glioma recurrence and radiation necrosis. A total of 44 patients--26 patients with recurrent malignant glioma, 10 patients with low grade glioma and 8 patients with radiation necrosis--underwent Tl SPECT. The patients had early SPECT images taken 15 minutes after intravenous injection of 3mCi of 201TlCl and also had delayed SPECT images taken 4 hours after injection. Count ratios of a lesion to normal brain (L/N) were calculated from the rectangular ROI for the quantitative analysis. Count ratios of the lesion seen on the delayed image to that on the early image (D/E) were also calculated. In 26 patients with recurrent malignant gliomas, L/N ratio ranged from 2.6 to 12.6 with a mean of 4.4 +/- 2.3 on early images. All patients had L/N ratios greater than 2.5. However, in 8 patients with cerebral radiation necrosis, L/N ratios ranged from 1.5 to 2.4 with a mean of 2.0 +/- 0.3 on early image. L/N ratios were always 2.5 or less. In 8 patients with cerebral radiation necrosis, there were little differences between the L/N ratios for early and delayed images. D/E ratios ranged from 1.0 to 1.3 with a mean of 1.2 +/- 0.1. These results confirmed the validity of Tl SPECT in differentiating cerebral radiation necrosis from recurrent malignant gliomas. In 10 patients with low grade astrocytoma there was a subtle uptake or no uptake of Tl and the ratios of these patients were rated at 1.0.(ABSTRACT TRUNCATED AT 250 WORDS)