EVALUATION OF THERAPEUTIC EFFECT BY POSITRON EMISSION TOMOGRAPHY USING FLUORINATED THYMIDINE DELIVATIVE

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We first evaluated the biodistribution of ^<18>F-FLT in mice. In addition to high uptake in xenografted tumor, FLT was shown to accumulate in lymphocytes activated by Concanavalin A stimulation.Clinical evaluation was conducted for 40 patients with brain tumors and other malignant tumors (53 examinations). Patients, who gave informed consent, were given intravenous injection of FLT. Image of the brain was obtained 40 minutes later by 20-min emission scan and 3-min transmission scan, and image of the body was obtained 50 min later by 3-min emission and 1-min transmission scan for 5 to 6 frames. Region of interest was set on the tumor and semi-quantitative value of uptake (SUV) was measured and compared with histological diagnosis.Uptake of FLT in brain tumors reflected the malignant grade of the tumor, and the FLT uptake in the tumor increased as the grade of the glioma increased. Uptakes in malignant lymphoma and in metastatic brain tumor were also in the range of malignant glioma. SUV of brain tumor showed positive relationship with the expression of cell proliferation marker, MIB-1.In cases, where recurrence of brain tumor was suspected, FLT-PET could detect malignant-transformed recurrent lesion correctly in some patients, while in other cases, spuriously high FLT uptake was observed in benign recurrent tumors and in granulomatous lesion.As for malignant tumors of the body trunk, high FLT uptake was observed for lung and pancreatic cancers. Evaluation of treatment effect was possible for 10 patients. Except for 2 patients with malignant lymphoma, showing low initial uptake, FLT uptake decreased during or early post-treatment, showing the possibility of FLT-PET for early prediction of treatment effect.