18F-Fluorodeoxyglucose-PET/CT to evaluate tumor, nodal disease, and gross tumor volume of oropharyngeal and oral cavity cancer: comparison with MR imaging and validation with surgical specimen

Introduction The purpose of this paper is to evaluate the impact of adding combined 18 F-PET/CT to MRI for T and N staging of the oral and oropharyngeal cancer and calculation of the gross tumor volume (GTV) having histopathology as reference standard. Methods PET/CT and MRI were performed in 66 patients with suspected oral and oropharyngeal cancer (41 primary tumors/25 recurrent tumors) and nodal disease (114 nodes). Statistical analysis included the McNemar test, sensitivity, specificity for the diagnostic modalities as well as regression analysis, and Bland–Altman graphs for calculated tumor volumes. Results There was no statistically significant difference between the two modalities compared to pathological findings regarding detection of disease ( P ≥ 0.72). The sensitivity/specificity for tumor detection were 100/80% and 96.72/60% for MRI and PET/CT, respectively. The sensitivity/specificity for nodal metastases were 88.46/75% and 83.81/73.91% for MRI and PET/CT, respectively. In 18% of cases, the MRI-based T staging resulted in an overestimation of the pathologic tumor stage. The corresponding rate for PET/CT was 22%. Regarding the treated necks, both modalities showed 100% sensitivity for detection of the recurrent lesions. In necks with histologically N0 staging, MRI and PET/CT gave 22% and 26% false positive findings, respectively. The mean tumor volume in the pathologic specimen was 16.6 ± 18.6 ml, the mean volume derived by the MR imaging was 17.6 ± 19.1 ml while the estimated by PET/CT volume was 18.8 ± 18.1 ml ( P ≤ 0.007 between the three methods). The Bland–Altman analysis showed a better agreement between PET/CT and MRI. Conclusion The diagnostic performance of FDG-PET/CT in the local staging of oral cancer is not superior to MRI.