A Head-to-Head Comparison of ⁶⁸Ga-DOTA-FAPI-04 and ¹⁸F-FDG PET/MR in Patients with Nasopharyngeal Carcinoma: A Prospective Study

Purpose: To conduct a head-to-head comparison of the diagnostic ability of ⁶⁸Ga-DOTA-FAPI-04 (⁶⁸Ga-FAPI) and ¹⁸F-FDG PET/MR in nasopharyngeal carcinoma (NPC) patients.

Methods: Patients diagnosed with NPC were prospectively enrolled. All patients underwent head-and-neck ⁶⁸Ga-FAPI PET/MR and ¹⁸F-FDG PET/MR within one week. Primary tumor, lymph node numbers, and tracer uptake were compared by SUVmax and visual evaluation. The primary tumor volumes derived from ⁶⁸Ga-FAPI, ¹⁸F-FDG PET, and MRI were also compared.

Results: Fifteen patients were enrolled from June to August 2020. Both ⁶⁸Ga-FAPI and ¹⁸F-FDG PET had 100% detection rate of the primary tumor. The ⁶⁸Ga-FAPI SUVmax of primary tumors (13.87±5.13) was lower than that of ¹⁸F-FDG (17.73±6.84), but the difference was not significant (p=0.078). Compared with ¹⁸F-FDG, ⁶⁸Ga-FAPI PET improved the delineation of skull-base invasion in eight out of eight patients and intracranial invasion in four out of four patients. When 25%SUVmax of ⁶⁸Ga-FAPI or 20%SUVmax of ¹⁸F-FDG was utilized as a threshold for determining tumor volume, it was highly consistent with MRI. ¹⁸F-FDG PET detected much more positive lymph nodes than ⁶⁸Ga-FAPI (100 vs 48). The SUVmax of 48 paired lymph nodes was significantly lower on ⁶⁸Ga-FAPI than ¹⁸F-FDG (8.67±3.88 vs 11.79±6.17, p<0.001). Additionally, ⁶⁸Ga-FAPI further detected four small, distant metastases in three patients. Compared with ¹⁸F-FDG, ⁶⁸Ga-FAPI changed overall staging in six of fifteen patients, with three patients being up-staged, and three down-staged.

Conclusions: ⁶⁸Ga-FAPI outperforms ¹⁸F-FDG in delineating the primary tumor and detecting distant metastases, particularly in the evaluation of skull-base and intracranial invasion, suggesting ⁶⁸Ga-FAPI hybrid PET/MR has the potential to serve as a single-step staging modality for patients with NPC. However, its value regarding lymph node evaluation needs further study.