Within-patient comparison between [68Ga]Ga-tilmanocept PET/CT lymphoscintigraphy and [99mTc]Tc-tilmanocept lymphoscintigraphy for sentinel lymph node detection in oral cancer: a pilot study

Purpose To compare sentinel lymph node (SLN) identification using [ 68 Ga]Ga-tilmanocept PET/CT lymphoscintigraphy to [ 99m Tc]Tc-tilmanocept lymphoscintigraphy (including SPECT/CT) in early-stage oral cancer. Furthermore, to assess whether reliable intraoperative SLN localization can be performed with a conventional portable gamma-probe using [ 99m Tc]Tc-tilmanocept without the interference of [ 68 Ga]Ga-tilmanocept in these patients. Methods This prospective within-patient comparison pilot study evaluated SLN identification by [ 68 Ga]Ga-tilmanocept PET/CT lymphoscintigraphy compared to conventional lymphoscintigraphy using [ 99m Tc]Tc-tilmanocept (~ 74 MBq) in 10 early-stage oral cancer patients scheduled for SLN biopsy. After conventional [ 99m Tc]Tc-tilmanocept lymphoscintigraphy, patients underwent peritumoral administration of [ 68 Ga]Ga-tilmanocept (~ 10 MBq) followed by PET/CT acquisition initiated 15 min after injection. Intraoperative SLN localization was performed under conventional portable gamma-probe guidance the next day; the location of harvested SLNs was correlated to both lymphoscintigraphic images in each patient. Results A total of 24 SLNs were identified by [ 99m Tc]Tc-tilmanocept lymphoscintigraphy, all except one were also identified by [ 68 Ga]Ga-tilmanocept PET/CT lymphoscintigraphy. [ 68 Ga]Ga-tilmanocept PET/CT lymphoscintigraphy identified 4 additional SLNs near the injection site, of which two harbored metastases. Lymphatic vessels transporting [ 68 Ga]Ga-tilmanocept were identified by PET/CT lymphoscintigraphy in 80% of patients, while draining lymphatic vessels were visualized by [ 99m Tc]Tc-tilmanocept lymphoscintigraphy in 20% of patients. Of the 33 SLNs identified by [ 68 Ga]Ga-tilmanocept PET/CT lymphoscintigraphy, 30 (91%) were intraoperatively localized under conventional gamma-probe guidance. Conclusion [ 68 Ga]Ga-tilmanocept PET/CT lymphoscintigraphy provided more accurate identification of SLNs and improved visualization of lymphatic vessels compared to [ 99m Tc]Tc-tilmanocept lymphoscintigraphy. When combined with peritumoral administration of [ 99m Tc]Tc-tilmanocept, SLNs detected by [ 68 Ga]Ga-tilmanocept PET/CT lymphoscintigraphy can be reliably localized during surgery under conventional gamma-probe guidance.