This is a phase II clinical trial to evaluate the capability of 68Ga-labeled targeted covalent radiopharmaceutical (TCR) fibroblast activation protein inhibitor (FAPI) PET/CT to guide the surgical treatment of medullary thyroid carcinoma (MTC). The surgical extent of MTC is determined based on the lesion range revealed by 68Ga-TCR-FAPI PET/CT, with the main endpoint being 1-month post-surgical calcitonin level.

Surgery remains the only curative option for MTC, yet the current imaging-based method (ultrasound, CT, MRI, 18F-FDG PET/CT) or calcitonin-based method are insufficient to map the extent of disease. In the previous studies, TCR-FAPI can covalently bind to FAP that increase tumor uptake and tumor retention, and better diagnosed MTC than the current radiotracers.

This is a phase II clinical trial to evaluate the capability of 68Ga-labeled targeted covalent radiopharmaceutical (TCR) fibroblast activation protein inhibitor (FAPI) PET/CT to guide the surgical treatment of medullary thyroid carcinoma (MTC). The surgical extent of MTC is determined based on the lesion range revealed by 68Ga-TCR-FAPI PET/CT, and the principles of surgery remains the same with differentiated thyroid carcinoma (i.e., lymph node dissection of level II-IV is required if lateral neck lymph node is considered metastasis). The primary endpoint of the study is 1-month post-surgical calcitonin level, and the secondary endpoints include the 2-year event free survival (EFS), the ratio of patient that change surgical plan, and the accuracy, sensitivity, specificity of 68Ga-TCR-FAPI PET/CT in identifying MTC lesions.

Patient will be divided into three arms: 1) newly diagnosed MTC and all 68Ga-TCR-FAPI PET/CT avid lesions are resected; 2) recurrent/persistent MTC and all 68Ga-TCR-FAPI PET/CT avid lesions are resected; 3) distant metastasis or unresectable lesions shown by 68Ga-TCR-FAPI PET/CT imaging but still recommended for surgical treatment. The three arms will not be compared between each other but will be separately analyzed.

Inclusion Criteria:

• Age between 18 and 75 years；
• Diagnosed with MTC and have surgical indication based on preliminary evaluation; the tumor may be newly diagnosed or previously treated;
• Expected survival of at least 12 weeks;
• No major organ dysfunction (heart, lung, liver, kidney and other major organ include), acute or life-threatening status of infection;
• Be willing and able to understand the research content and provide written informed consent/assent for the trial.

Exclusion Criteria:

• Have a history of imaging agent allergies;
• Does not meet the PET-CT scan sedation requirements, or has contraindications for PET-CT examination;
• Be pregnant or breastfeeding, or expecting to conceive or father children within the projected duration of the trial;
• No surgical indication (i.e., no measurable disease, unresectable disease, or significant present of distant metastasis), refusing surgery or 68Ga-TCR-FAPI PET/CT-guided surgery.