18F-Dihydroxyphenylalanine PET in patients with biochemical evidence of medullary thyroid cancer:: Relation to tumor differentiation

Curative treatment for recurrent medullary thyroid cancer (MTC), diagnosed by rising serum calcitonin, is surgery, but tumor localization is difficult. Therefore, the value of (18)F-dihy-droxyphenylanaline PET ((18)F-DOPA PET), (18)F-FDG PET, (99m)Tc-V-di-mercaptosulfuricacid (DMSA-V) scintigraphy, and MRI or CT was studied. Methods: Twenty-one patients with biochemical recurrent or residual MTC underwent (18)F-DOPA PET, (18)F-FDG PET, DMSA-V scintigraphy, and MRI or CT. Patient- and lesion-based sensitivities were calculated using a composite reference consisting of all imaging modalities. Results: In 76% of all patients with MTC, one or more imaging modalities was positive for MTC lesions. In 6 of 8 patients with a calcitonin level of < 500 ng/L, imaging results were negative. In 15 patients with positive imaging results, (18)F-DOPA PET detected 13 (sensitivity, 62%; with 4.6 lesions per patient [Ipp]). Morphologic imaging (n = 19) was positive in 7 (sensitivity, 37%; 4.7 Ipp), DMSA-V (n - 18) in 5 (sensitivity, 28%; 1.1 Ipp), and (18)F-FDG PET (n = 17) in 4 (sensitivity, 24%; 1.6 Ipp). In a lesion-based analysis, (18)F-DOPA PET detected 95 of 134 lesions (sensitivity, 71 %), morphologic imaging detected 80 of 126 (sensitivity, 64%), DMSA-V detected 20 of 108 (sensitivity, 19%), and (18)F-FDG PET detected 48 of 102 (sensitivity, 30%). in 2 of 3 patients with a calcitonin/carcinoembryonic antigen (CEA) doubling time of <= 12 mo, (18)F-FDG PET performed better than (18)FDOPA PET; in the third patient, (18)F-FDG PET was not performed. Conclusion: MTC lesions are best detectable when serum calcitonin was > 500 ng/L. (18)F-DOPA PET is superior to (18)F-FDG PET, DMSA-V, and morphologic imaging. With short calcitonin doubling times (<= 12 mo), (18)F-FDG PET may be superior.