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 amino acid transport and is suitable for SPECT. Methods: To determine whether tumors outside the brain can also accumulate this tracer, we injected 300-450 MBq IMT into 20 patients with different tumors [5 breast cancers, 4 lung tumors (1 benign), 2 carcinoid liver metastases, 4 soft-tissue tumors (1 benign), 3 malignant lymphomas and 2 primary brain tumors]. Tumor size ranged from 1-12 cm. Imaging was repeated after radiotherapy in two patients with breast cancer. Histology was available in all cases. Dynamic scans, whole-body imaging and SPECT were performed during the first hour and 3 hr after injection. Plasma samples were analyzed for IMT, free I-123 and other metabolites. Results: All primary 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 peaked in the first hour. Two carcinoid lesions in the liver tumors exhibited no IMT uptake above liver background. Tumor-to-background ratios in a benign bone inflammatory process and a focal pulmonary vasculitis were less than 1,2 (planar) and 1.9 (SPECT) and could be differentiated from uptake in all malignant nonbrain tumors. IMT was rapidly cleared from the plasma [3.6% +/- 0.6% (mean +/- s.d.) injected dose/liter at 10 min postinjection]. Minor in vivo deiodination was present (