Whole-body PET with [11C]-5-hydroxytryptophan for localization of neuroendocrine tumors

• Purpose: [11C]-5-Hydroxytryptophan (5-HTP) has previously been shown to be an excellent tracer for localization of neuroendocrine tumors, especially hormone-producing midgut carcinoids. To improve the clinical usefulness of 5-HTP PET in a diagnostic setting, we wanted to develop a whole-body scanning approach.Methods: The patients received 200 mg carbidopa orally as premedication to block physiological decarboxylation, thereby improving tumor/background contrast. Two hundred to 800 MBq of 5-HTP was injected in a forearm vein. Ten minutes post-injection emission scanning was performed, covering thorax and abdomen in whole-body mode. In a GE4096 scanner (10 cm FOV), a protocol of up to 6 bed positions with timeframes of 5, 7, 10, 10, 15, and 20 minutes was used. In a Siemens CTI Ecat HR+ scanner (15.5 cm FOV), 4 bed positions with timeframes of 7, 10, 15, and 20 minutes was used. Transmission scans were performed for 2–4 minutes for each bed position and segmented for attenuation correction. Comparison with CT, octreotide scintigraphy, and surgical end points were made.Results: So far 50 patients referred for staging of carcinoid tumors, localization of ectopic ACTH-producing tumors or endocrine pancreatic tumors have been investigated. 5-HTP generally shows more lesions than CT and in some cases more lesions and lesions at an earlier stage than octreotide scintigraphy. Clinical trials have been set up to define the role of 5-HTP whole-body scans in routine clinical use.Conclusions: Whole-body PET with 5-HTP is a promising new approach in diagnostic imaging of neoplasias of neuroendocrine origin, evidently changing treatment planning in selected patient groups. (Clin Pos Imag 1999;2:338) All rights reserved.

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