Postsurgical medullary thyroid cancer patients who have elevated calcitonin levels, which can indicate that the cancer has returned, are well served with follow-up PET/CT using the radiotracer ¹⁸F-DOPA (fluorine-18-L-dihydroxyphenylalanine), according to a small study published online May 30 in Nuclear Medicine Communications.

Researchers at the University of Zagreb in Croatia scanned 28 patients with ¹⁸F-DOPA PET/CT after other imaging exams—including neck ultrasound and CT of the thorax, abdomen and/or pelvis—came back negative.

The patients were selected for the additional imaging because they had increasing calcitonin in visits following total thyroidectomy for medullary cancer. The mean follow-up period was 19.7 months.

The team reports that ¹⁸F-DOPA PET/CT turned up positive findings in 57 percent of the patients (16 out of 28), mostly because of metabolically active neck and mediastinal lymph nodes metastases.

Further, previously unknown bone metastases were found in six patients, and a positive scan was reported in four patients (25 percent of positive scans) with a very low calcitonin value.

The PET/CT results led to a change of management and therapy in 16 of the 28 positive patients. The modified care paths included surgery for eight patients, radiotherapy for five and chemotherapy for two.

The authors conclude that ¹⁸F-DOPA PET/CT “is a clinically useful modality in medullary thyroid carcinoma whenever the calcitonin level is increased.”

“There is a clear trend toward more positive scans with the higher calcitonin values,” they add, “but patients with moderately elevated calcitonin values should also be taken into consideration for molecular imaging with ¹⁸F-DOPA PET/CT as the tumor burden in these patients is probably low, enabling further therapy to be individualized and consequently more efficient.”