Clinical values of ¹⁸FDG PET-CT and MRI in precise radiotherapy after surgery in patients with oropharyngeal squamous cell carcinoma

Objective: To investigate the clinical values of ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸FDG PET-CT) and magnetic resonance imaging (MRI) in precise radiotherapy after surgery in patients with oropharyngeal squamous cell carcinoma. Methods: A total of 53 patients with oropharyngeal squamous cell carcinoma were enrolled and underwent PET-CT and MRI imaging within two weeks after surgery. The detection rates of residual lesions and lymph node metastases after surgery by PET-CT and MRI were compared on the basis of the pathological results of biopsy. The gross tumor volume (GTV) and clinical target volume (CTV) determined by PET-CT and MRI were compared; the normally distributed data were analyzed using the t test, and the skewed distribution data by the Wilcoxon rank sum test. The sensitivity, specificity, accuracy, positive predictive value and negative predictive value in predicting precise radiotherapy after surgery, as determined by PET-CT and MRI, were compared with the chi-square test. Results: Fourteen patients had residual lesions after surgery. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of PET-CT in detecting residual lesions after surgery were significantly higher than those of MRI (92.86%, 94.87%, 86.67%, 97.37%, and 94.34% vs. 57.14%, 76.92%, 47.06%, 83.34%, and 71.70%, all P < 0.05); the specificity, positive predictive value, and accuracy of PET-CT in detecting lymph node metastases were also significantly higher than those of MRI (all P < 0.05), except for the sensitivity and negative predictive value (P > 0.05). For the 14 patients with residual lesions, GTV_PET/CT was significantly smaller than GTV_MRI(45.62 ± 22.13 cm³ vs. 60.61 ± 23.12 cm³, P = 0.034), so did CTV (125.54 ± 17. 53 cm³ vs. 142.18 ± 21.22 cm³, P = 0.011). There was no significant difference between CTV_PET/CT and CTV_MRI in 39 patients without residual lesions after surgery (117.87 ± 17.66 cm³ vs. 128.05 ± 20.65, P = 0.099). Conclusions: PET-CT is superior to MRI in detecting the residual lesions and lymph node metastases after surgery in patients with oropharyngeal squamous cell carcinoma, which provides valuable information for radiotherapy planning. (authors)