FEASIBILITY OF TUMOR IMAGING USING L-3-[IODINE-123]-IODO-ALPHA-METHYL-TYROSINE IN EXTRACRANIAL TUMORS

L-3-[I-123]-lodo-alpha-methyl-tyrosine (IMT) is a modified amino acid. It is reported to be avidly taken up in brain tumors, reflecting amin o acid transport and is suitable for SPECT. Methods: To determine whet her tumors outside the brain can also accumulate this tracer, we injec ted 300-450 MBq IMT into 20 patients with different tumors [5 breast c ancers, 4 lung tumors (1 benign), 2 carcinoid liver metastases, 4 soft -tissue tumors (1 benign), 3 malignant lymphomas and 2 primary brain t umors]. Tumor size ranged from 1-12 cm. Imaging was repeated after rad iotherapy in two patients with breast cancer. Histology was available in all cases. Dynamic scans, whole-body imaging and SPECT were perform ed during the first hour and 3 hr after injection. Plasma samples were analyzed for IMT, free I-123 and other metabolites. Results: All prim ary tumors were visualized. Tumor-to-background ratios ranged from 1.1 to 3.8 on planar and from 1.3 to 6.2 on SPECT images. Tumor uptake pe aked in the first hour. Two carcinoid lesions in the liver tumors exhi bited no IMT uptake above liver background. Tumor-to-background ratios in a benign bone inflammatory process and a focal pulmonary vasculiti s were less than 1,2 (planar) and 1.9 (SPECT) and could be differentia ted from uptake in all malignant nonbrain tumors. IMT was rapidly clea red from the plasma [3.6% +/- 0.6% (mean +/- s.d.) injected dose/liter at 10 min postinjection]. Minor in vivo deiodination was present (<1% of injected dose 1 hr postinjection). No other metabolites were found . Normal distribution consists of some uptake in the brain, liver, spl een, muscles, pancreatic region and intestinal structures and massive uptake and excretion in the kidneys and bladder. Conclusion: IMT has p otential as a metabolic tracer in tumors outside the brain.