RETENTION INDEX OF TL-201 SINGLE-PHOTON EMISSION COMPUTERIZED-TOMOGRAPHY (SPECT) AS AN INDICATOR OF METASTASIS IN ADENOCARCINOMA OF THE LUNG

We examined the relationship between the retention of thallium-201 (Tl -210) on a delayed scan and the metastatic potential of adenocarcinoma s of the lung. We studied 43 patients with adenocarcinoma of the lung and divided them into two groups according to the presence or absence of lymph node metastasis. Tl-201 single photon emission computerised t omography (SPECT) was conducted twice: 15 min (early scan) and 120 min (delayed scan) after intravenous injection of 3 mCi of Tl-201 chlorid e. We calculated the retention index in order to evaluate the degree o f Tl-201 retention in the primary tumour. The retention indices were s ignificantly higher in the group that was positive for lymph node meta stasis than in the negative group. In adenocarcinomas with high metast atic potential, Tl-201 SPECT demonstrated slow washout or increased re tention on the delayed scan. The retention index of Tl-201 SPECT is a useful indicator of metastatic potential, thereby facilitating the pre diction of prognosis, and provides insight into the relationship betwe en Tl-201 uptake and malignancy. This is the first report demonstratin g a significant relationship between the retention of Tl-201 SPECT and lymph node metastasis.