THALLIUM IMAGING FOR BRAIN-TUMORS WITH RESULTS MEASURED BY A SEMIQUANTITATIVE INDEX AND CORRELATED WITH HISTOPATHOLOGY

Background. The optimal management of patients with brain tumors requi res knowledge of the tumor characteristics upon presentation and the d iscovery of recurrence after therapy. Thallium-201 (Tl-201) chloride h as shown varying uptake in tumors, depending on their viability and th e type and degree of malignancy. This study explores the diagnostic po tential of thallium imaging in patients with brain tumors. Methods. Fo rty-three Tl-201 single photon emission computed tomographic scintigra ms were performed on 40 patients with intracranial neoplasms, nearly e qually divided between patients with no prior treatment and patients w ho had prior treatment and were suspected to have recurrent tumor and/ or radiation necrosis. A thallium tumor index was calculated as the ra tio of counts for a region of interest drawn in the lesion area and it s mirror image in normal brain tissue. A two-tailed Student's t test w as performed to compare the thallium index and histopathologic finding s. Results. A value of 1.5 for the thallium tumor index allowed for th e best correlation between the prediction of malignancy and the histop athologic results. In the pretreatment group, a thallium tumor index g reater than 1.5 correlated with high grade malignancy, and less than 1 .5 correlated with either a well differentiated astrocytoma or benign cyst. In the posttreatment group, a thallium tumor index greater than 1.5 correlated with recurrent and/or residual malignant tumor. Conclus ions. For those patients undergoing initial evaluation, the thallium s tudy can help in the differential diagnosis of an intracranial mass le sion and offers confirmation of results of biopsy. For those patients who already have received treatment, the study can be used to detect r ecurrent or residual tumor.