Utilization of [Ga68]FAPI PET/CT in the Evaluation of Thyroid Nodules with 'Suspected' or ‘Malignant’ FNAB: Preliminary Results

Abstract

Abstract OBJECTIVE: Fine needle aspiration biopsy (FNAB) is the standard diagnostic approach for identifying thyroid cancer. However, there are challenges with FNAB, such as its invasiveness and the need for repeat procedures based on suspected cytology results. Stroma-targeted PET imaging, using 68Ga-FAPI PET/CT, has shown promising results in detecting tumors and may be a less invasive tool to differentiate between malignant and indeterminate thyroid nodules. METHODS: This prospective registry study included twenty two patients with tweny four nodules. 68Ga-FAPI PET/CT was performed after fine needle aspiration biopsy (FNAB). Any non-physiological uptake greater than adjacent normal tissue background on 68Ga-FAPI PET/CT was included in the study. The TBR (tumor to background ratio) was defined as the ratio of the lesions’ SUVmax and the SUVmax of healthy thyroid parenchyma tissue determined for each reconstruction algorithm. All the patients had undergone thyroidectomy to confirm the results of FNAB. The post operation histological specimen were also taken as the reference standard. Post-op histopathology, FNAB results and TBR values on 68Ga-FAPI FAPI PET/CT were compared. RESULT: The study found that malignant thyroid nodules had significantly higher mean SUVmax values compared to benign nodules. However, there was no significant difference in activity uptake between the backgrounds of the nodules. The tumor-to-background ratio (TBR) was higher in malignant nodules, although statistical significance was not reached. Non-follicular types of malignant nodules exhibited significantly higher SUVmax and TBR values compared to follicular variants and benign nodules. There was no significant difference in activity uptake in the backgrounds. Non-follicular types consistently showed higher SUVmax and TBR values, while follicular variants did not display significant activity uptake compared to benign nodules. CONCLUSION: Due to highly significant SUVmax correlation between benign nodules and background, TBR could be more reliable point of reference in evaluation of thyroid nodules. Non-follicular types of PTC showed significantly higher SUVmax values and prominent TBR compared to follicular variants and benign nodules. After re-categorization, 68Ga-FAPI PET/CT showed 100% sensitivity and NPV in detection of non-follicular types of PTC.