Comparative Study Of 68Ga-FAP1-04 PET/CT And 18F-FDG PET/CT In The Diagnosis And Staging Of Head And Neck Tumors

Objective:To compare the value of ⁶⁸Ga-FAPI-04 PET/CT and¹⁸F-FDG PET/CT in the diagnosis and staging of head and neck tumors.Methods:Forty-five patients with head and neck tumors were finally included in this study,and all of them underwent ⁶⁸Ga-FAPI-04PET/CT and ¹⁸F-FDG PET/CT imaging.The reference criteria for the final diagnosis included pathological examination,imaging（enhanced CT,MRI,bone scan,etc）and subsequent imaging follow-up results.The detection rates of primary foci,lymph node metastases,distant metastases and false-positive lesions were compared between the two imaging methods.The initial staging of patients with head and neck tumors was performed separately using the two images,and the concordance between the two in staging was compared.The display of primary lesions was visually assessed.The maximum standardized uptake value（SUVmax）of the primary tumor and the mean standardized uptake value（SUVmean）of the non-tumor tissue were measured in the two images separately.The target-to-background ratio（TBR）was calculated.The statistical differences between SUVmax and TBR of the two imaging types were compared and analyzed,and the area under the curve（AUC）of SUVmax and TBR were compared to find the optimal diagnostic threshold of SUVmax and TBR for head and neck tumors.Spearman’s rank correlation test was used to analyze the correlation between SUVmax of primary foci and metastatic lymph nodes and the long diameter,and to correlate the SUVmax of primary foci between the two imaging agents.Results:This retrospective study ultimately included 45 patients with histopathologically confirmed head and neck tumors,including 32nasopharyngeal,4 hypopharyngeal,3 laryngeal,4 oral,1 nasal,and 1maxillofacial.There were 41 squamous,1 adenocarcinoma,1 malignant melanoma,and 2 sarcomas of the 45 patients.（1）The detection rate of primary tumors was 97.78%（44/45）for both imaging methods,and the visual assessment of more primary lesions（25/45）was better with FAPI PET/CT.The SUVmax of primary lesions in FAPI and ¹⁸F-FDG PET/CT were 10.90±0.86 and 10.45±0.81,respectively,and the differences were not statistically significant.The TBR of primary lesions in two imaging methods were 11.50（5.55,17.55）and 9.80（5.80,12.80）,respectively,with P<0.01,and the results were statistically significant.The SUVmax of the primary tumor in both FAPI and ¹⁸F-FDG PET/CT showed a moderately strong positive correlation with the lesion length diameter,r=0.472 and 0.450,respectively,P<0.05.The SUVmax of the primary tumor between the two imaging agents showed a stronger degree of positive correlation,r=0.628,P<0.001.（2）For ROC curve analysis of SUVmax,FAPI-AUC was 0.904 and FDG-AUC was 0.685,corresponding to optimal diagnostic cut-off values of 6.1 and 10.4,respectively,with statistically significant differences（z=2.458,P=0.014）.For ROC curve analysis of TBR,FAPI-AUC was 0.859 and FDG-AUC was 0.578,corresponding to the optimal diagnostic cut-off values of 2.2and 3.9,respectively,with statistically significant differences（z=2.082,P=0.037）.（3）The detection rate of lymph node metastasis was 90.48%（209/231）for FAPI PET/CT and 96.54%（223/231）for ¹⁸F-FDG PET/CT.The detection rate of false-positive lymph nodes was 17.46%（11/63）and95.24%（60/63）,respectively.The SUVmax of metastatic lymph nodes in FAPI and ¹⁸F-FDG PET/CT were 6.9（4.3,10.4）and 6.5（4.3,11.5）,respectively,and the differences were not statistically significant.The SUVmax of metastatic lymph nodes in both imaging showed a moderately strong positive correlation with the length diameter,r was0.486 and 0.596,respectively,P<0.01.（4）The detection rate of distant metastases was 75%（12/16）for FAPI PET/CT and 87.5%（14/16）for¹⁸F-FDG PET/CT,and the detection rates of false-positive lesions were70%（7/10）and 50%（5/10）for both,respectively.The detection rates of lung metastases,bone metastases,liver metastases and adrenal metastases for both were 50%（2/4）vs 100%（4/4）,83.3%（5/6）vs 66.7%（4/6）,80%（4/5）vs 100%（5/5）,and 100%（1/1）vs 100%（1/1）,respectively.The SUVmax of pulmonary metastases in FAPI and ¹⁸F-FDG PET/CT were4.90±2.14 and 6.25±2.20,respectively.And liver metastases were 3.58±0.58 and 6.72±0.12,respectively.The differences of pulmonary and liver were statistically significant.The differences in SUVmax between bone metastases and adrenal metastases in the two imaging were not statistically significant.（5）The number of cases with errors in T,N,and M staging in FAPI PET/CT was less than that of ¹⁸F-FDG PET/CT in 45patients with head and neck tumors.In FAPI PET/CT,T-stage was upregulated in 6 patients.T-stage was underestimated in 2 patients.N-stage and M-stage was underestimated in 1 patient respectively.In¹⁸F-FDG PET/CT,N-stage was underestimated in 1 patient and M-stage was underestimated in 1 patient.N-stage was overestimated in 7 patients and M-stage was overestimated in 1 patient.For overall staging,FAPI PET/CT improved the total staging in 8 patients（up-regulated in 4patients and down-regulated in 4 patients）,although it underestimated the total staging in 2 patients.The agreement between the two imaging staging was 77.78%（35/45）.Conclusion:（1）FAPI PET/CT was comparable to ¹⁸F-FDG PET/CT for the detection of primary head and neck tumors,with better visual assessment of most lesions,demonstrating an excellent target-to-background ratio and favoring the display of skull base and intracranial invasion.（2）The detection rate of lymph node metastases by FAPI PET/CT was lower than that by ¹⁸F-FDG PET/CT,but greatly reduced the detection of false positive lymph nodes.（3）FAPI PET/CT is more advantageous than ¹⁸F-FDG PET/CT in detecting bone metastases,but less accurate than ¹⁸F-FDG PET/CT in detecting lung metastases and liver metastases.（4）FAPI PET/CT is more accurate than ¹⁸F-FDG PET/CT in detecting T-stage,N-stage and M-stage of head and neck tumors.The combined use of both imaging methods can improve the initial staging of head and neck tumors.⁶⁸Ga-FAPI-04,as a new PET imaging agent,improves patients’comfort and optimizes workflow,and has clinical value for the diagnosis and staging of head and neck tumors.