PREDICTING CHEMOTHERAPEUTIC RESPONSE TO SMALL-CELL LUNG-CANCER OF PLATINUM COMPOUNDS BY TL-201 SINGLE-PHOTON EMISSION COMPUTERIZED-TOMOGRAPHY

Thallium-201 single-photon emission computerized tomography (SPECT) wa s used to clarify the relationship between (TI)-T-201 uptake and the r esponse in chemotherapy to platinum compounds in 21 patients with smal l-cell lung cancer. Tl-201-SPECT scans were obtained twice: at 15 min (early scan) and 120 min (delayed scan) after an intravenous injection of 111 MBq (3 mCi) of thallium-201 chloride. We obtained the uptake r atio from each scan and calculated the retention index:uptake ratio = region of interest uptake / contralateral normal lung uptake; retentio n index = (delayed ratio - early ratio)/early ratio. After (TI)-T-201 scintigraphy, 12 patients received chemotherapy consisting of platinum compounds and nine were treated with chemoradiation. Among patients r eceiving only chemotherapy, the retention index correlated with the re sponses to chemotherapy. In an in vitro study, ouabain, an inhibitor o f the Na,K-ATPase pump, reduced sensitivity to cisplatin and inhibited intracellular thallium uptake in the small-cell lung cancer cell line . These studies suggest that (TI)-T-201-SPECT is a useful indicator of response to chemotherapy with platinum compounds in small-cell lung c ancer, and that Na,K-ATPase is commonly involved in transporting both thallium and platinum compounds into cancer cells.