Specific localization of thallium 201 in human high-grade astrocytoma by microautoradiography

The ability to accurately distinguish remaining or recurrent high-grade astrocytoma from necrosis or edema following treatment is essential to optimal patient management. Thallium 201 planar gamma-camera imaging has been shown to be helpful in detecting recurrent high-grade astrocytoma; however, due to tissue heterogeneity adjacent to and within tumor, the cellular specificity and quantification of 201Tl uptake are largely unknown. In order to determine which tissues are responsible for the radioisotope uptake, microautoradiographic techniques were used to examine multiple tissue sections from five patients with high-grade astrocytoma. Each patient received 5 mCi of 201Tl i.v. 1 h prior to tumor removal. Additionally, all patients received computerized tomographic and 201Tl planar gamma-camera scans prior to surgery. Following surgery, the excised tissue specimens were tentatively classified by gross pathological examination and then immediately processed for dry mount autoradiography; grain density was determined over regions containing tumor, adjacent and uninvolved brain tissue, necrotic tissue, and background. Highly significant differences were found in grain densities (201Tl uptake) between tumor and uninvolved brain tissue, as well as between uninvolved brain tissue and necrotic tissue; there was no significant difference between background grain density and that in necrotic tissue. Mean grain densities (grains/cm2 +/- 1 SD) across patients were: tumor, 102 +/- 23; adjacent, uninvolved brain tissue, 29 +/- 11; necrotic tissue, 6.2 +/- 1.1; and background, 7.0 +/- 4.1. We conclude that the ability of 201Tl to selectively image high-grade astrocytoma is due to its preferential uptake into tumor cells.