Specific Localization of Thallium 201 in Human High-Grade Astrocytoma by Microautoradiography1

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 -y-caméra 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 '"'II 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 '"'TI i.v. l h prior to tumor removal. Addition ally, all patients received computerized tomographic and ;'"T1 planar 7camera 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 signifi cant differences were found in grain densities (''"'II 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 back ground, 7.0 ±4.1. We conclude that the ability of :'"TI to selectively image high-grade astrocytoma is due to its preferential uptake into tumor cells.