The value of 18F-DOPA PET/CT in patients with medullary thyroid carcinoma and increased calcitonin values.

Abstract

The aim of this prospective observational study was to examine the benefit of a fluorine-18-L-dihydroxyphenylalanine (F-DOPA) PET/computed tomography (CT) scan in patients with medullary thyroid carcinoma (MTC) in terms of increased calcitonin levels. Twenty-eight MTC patients after initial total thyreoidectomy with increasing follow-up calcitonin levels suggestive for active disease after negative conventional imaging findings (neck ultrasound or thorax, abdomen, pelvis multislice computed tomography as standard imaging) were scanned using F-DOPA PET/CT from November 2012 to April 2016. The mean calcitonin level was 108.5 (range: 6.7-290) pmol/l and the mean carcinoembryonic antigen level was 15.7 (range: 1.1-221.9) μg/l. The mean follow-up period was 19.7 months. F-DOPA PET/CT was positive in 16 out of 28 (57%) patients, mostly because of metabolically active neck and mediastinal lymph nodes metastases. Previously unknown bone metastases were found in six patients. A positive scan was reported in four patients (25% of positive scans) with a very low calcitonin value of less than 49.9 pmol/l. PET/CT findings led to a change of management and therapy in 16 out of 28 patients, with surgical procedure performed in eight patients, radiotherapy in five patients, and chemotherapy in two patients. F-DOPA PET/CT is a clinically useful modality in MTC whenever the calcitonin level is increased. There is a clear trend toward more positive scans with the higher calcitonin values, but patients with moderately elevated calcitonin values should also be taken into consideration for molecular imaging with F-DOPA PET/CT as the tumor burden in these patients is probably low, enabling further therapy to be individualized and consequently more efficient.