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L-3-[¹²³I]Iodo--Methyltyrosine Scintigraphy in Carcinoid Tumors: Correlation with Biochemical Activity and Comparison with [¹¹¹In-DTPA-D-Phe¹]-Octreotide Imaging

Departments of Nuclear Medicine, Medical Oncology, and Pathology & Laboratory Medicine, University Hospital Groningen, Groningen, The Netherlands

Carcinoid tumors can produce serotonin (5-hydroxytryptamine) and catecholamines from the precursors tryptophan and tyrosine. Our aim was to evaluate the tyrosine analog L-3-[¹²³I]iodo--methyltyrosine (IMT) in the detection and the determination of biochemical activity of these tumors in comparison with ¹¹¹In-labeled [diethylenetriaminepentaacetic acid (DTPA)-D-Phe¹]-octreotide (¹¹¹In-octreotide) scintigraphy. Methods: SPECT and planar whole-body imaging were performed 15 min after administration of 300 MBq IMT in 22 patients with metastatic carcinoid tumors. The number of lesions detected was compared with the number detected by ¹¹¹In-octreotide scintigraphy. The size and intensity of uptake of all lesions were graded using a simple scoring system, yielding a total body uptake score for both tracers. These scores were compared (nonparametric correlation) with biochemical markers of serotonin and catecholamine metabolism. Results: IMT SPECT detected only 63 of 145 lesions detected by ¹¹¹In-octreotide imaging (43%). IMT SPECT performance was best in the liver (60% detection rate). Both IMT uptake and ¹¹¹In-octreotide uptake scores correlated with markers of serotonin metabolism (respective values for urinary 5-hydroxyindoleacetic acid: r = 0.67 and 0.48, P < 0.001 and 0.05; for urinary serotonin: r = 0.56 and 0.40, P = 0.002 and 0.05; and for platelet serotonin: r = 0.57 and 0.45, P < 0.01 and 0.05). No correlation with adrenaline or noradrenaline metabolites was found. However, IMT uptake, but not ¹¹¹In-octreotide uptake, correlated with dopamine metabolite excretion (homovanillic acid: r = 0.60, P < 0.05; and dopamine relative sum: r = 0.61, P < 0.05). IMT uptake was higher in patients with increased dopamine metabolite excretion (P = 0.05). Conclusion: IMT uptake can be demonstrated in carcinoid lesions, but the method detected only 43% of carcinoid lesions that were positive on ¹¹¹In-octreotide scintigraphy. Uptake of both tracers is related to the serotonin secretory activity. However, IMT uptake, but not ¹¹¹In-octreotide uptake, was related to tumor dopamine metabolism. These findings may be of interest in the metabolic targeting of carcinoids.

Key Words: ¹²³I-methyltyrosine • carcinoid tumors • secretory activity • ¹¹¹In-octreotide

Received Sep. 8, 1999; revision accepted Apr. 4, 2000.

For correspondence contact: Pieter L. Jager, MD, Department of Nuclear Medicine, University Hospital Groningen, P.O. Box 30001, 9700 RB Groningen, The Netherlands.

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