Initial Clinical Investigation of [18F]Tetrafluoroborate PET/CT in Comparison to [124I]Iodine PET/CT for Imaging Thyroid Cancer.

AIM: Recently, [F]tetrafluoroborate ([F]TFB) has been introduced as a versatile PET probe for imaging the human sodium/iodide symporter activity. This pilot study aimed to compare [F]TFB-PET/CT with [I]NaI-PET/CT imaging in thyroid cancer patients.

METHODS: Nine patients with newly diagnosed differentiated thyroid cancer underwent both [F]TFB- and [I]NaI-PET/CT after total thyroidectomy. PET/CT scans were visually analyzed for the presence of remnant thyroid tissue and for metastatic lesions on a patient and lesion basis. For semiquantitative analysis, thyroid remnant/tumor to blood pool ratios were calculated.

RESULTS: All patients presented with positive [F]TFB and [I]NaI-PET/CT scans. Retention of I in remnant thyroid tissue was significantly higher as compared with [F]TFB (P < 0.01). In a lesion-based analysis, both tracers identified an almost equal number of foci with [F]TFB depicting a total of 41 foci and I a total of 40 foci, respectively. In 6 of 9 patients, both radiopharmaceuticals returned an identical number of foci. Two I-positive benign thyroid remnants were missed by [F]TFB-PET/CT in a single patient. In another case, both tracers identified different thyroid remnant tissues in the cervical region. Notably, [F]TFB demonstrated additional (I-negative) cervical lymph node metastases in 2 patients, leading to an overall agreement between the radiotracers of 91% (74/81 foci).

DISCUSSION: In this pilot study, [F]TFB-PET was not inferior to [I]NaI-PET for detecting thyroid cancer and its metastases and was able to detect [I]NaI-PET-negative viable differentiated thyroid cancer metastases. Further clinical evaluation as a PET tracer for imaging thyroid pathophysiology and human sodium/iodide symporter expressing neoplasms is highly warranted.