Sentinel lymph node detection in thyroid carcinoma using [⁶⁸Ga]Ga-tilmanocept PET/CT: a proof-of-concept study

Purpose: Sentinel lymph node (SLN) biopsy is rarely used for thyroid carcinoma staging. This is due to challenges associated with conventional Tc-99m-labeled tracers, often producing a large hotspot at the injection site, potentially hiding nearby SLNs (shine-through effect). The aim of this study was to demonstrate the feasibility and effectiveness of SLN visualization using the new PET tracer [⁶⁸Ga]Ga-tilmanocept.

Methods: Patients with thyroid carcinoma underwent ultrasound-guided peritumoral injection of [⁶⁸Ga]Ga-tilmanocept and ICG-[^99mTc]Tc-nanocolloid. [⁶⁸Ga]Ga-tilmanocept PET/CT scans were conducted at 15 min and 60 min post-injection to visualize the SLNs. SLN biopsy was performed using ICG-[^99mTc]TC-nanocolloid for intraoperative identification. The corresponding lymph node level was resected for reference.

Results: Seven differentiated thyroid carcinoma (DTC) and 3 medullary thyroid carcinoma (MTC) patients were included, of which 6 were clinically node-negative. The median number of SLNs detected on [⁶⁸Ga]Ga-tilmanocept PET/CT and resected was 3 (range 1-4) and 3 (range 1-5), respectively. Eight SLNs were found on PET/CT in the central compartment and 19 in the lateral compartment. The SLN procedure detected (micro)metastases in all patients except one. Seventeen of 27 pathologically assessed SLNs were positive, 8 negative, and 2 did not contain lymph node tissue, which led to upstaging in 5 out of 6 clinically node-negative patients.

Conclusions: [⁶⁸Ga]Ga-tilmanocept PET/CT identified SLNs in all patients, mainly in the lateral neck. The SLNs were successfully surgically detected and resected using ICG-[^99mTc]Tc-nanocolloid. This technique has the potential to improve neck staging, enabling more personalized treatment of thyroid cancer according to the lymph node status.

Trial registration: 2021-002470-42 (EudraCT).