Evaluation of Dual-Timepoint 18F-FDG PET/CT Imaging for Lymph Node Staging in Vulvar Cancer

Abstract

This study aimed to assess the value of dual-timepoint ¹⁸F-FDG PET/CT in the prediction of lymph node (LN) status in patients with invasive vulvar cancer (VC) scheduled for inguinofemoral LN dissection. Methods: From April 2013 to July 2015, all consecutive patients with VC scheduled for inguinofemoral LN dissection were prospectively enrolled. All patients underwent a preoperative whole-body ¹⁸F-FDG PET/CT scan at 1 h (standard examination) and an additional scan from T11 to the groins at 3 h (delayed examination) after ¹⁸F-FDG injection. On both scans, each groin was visually scored 0 or 1 concerning ¹⁸F-FDG LN uptake relative to background. Semiquantitative analysis included SUV_max and the corresponding retention index of SUV_max, measured on both scans. The optimal cutoff value of these parameters was defined using a receiver-operating-characteristic analysis. Histopathology was the standard of reference. Results: Thirty-three patients were included, with a total of 57 groins dissected and histologically evaluated. At histopathology, 21 of 57 (37%) groins contained metastatic LNs. Concerning visual score, sensitivity, specificity, negative predictive value, positive predictive value, and accuracy were 95.2%, 75%, 96.4%, 69%, and 82.5% on standard scanning and 95.2%, 77.8%, 96.6%, 71.4%, and 84.2% on delayed scanning, respectively. At receiver-operating-characteristic analysis, sensitivity and specificity were 95.2% and 77.8% on standard and delayed ¹⁸F-FDG PET/CT for an SUV_max cutoff of greater than 1.32 and 1.88, respectively, and 95.2% and 80% for a retention index of SUV_max cutoff of greater than 0. Conclusion: Standard ¹⁸F-FDG PET/CT is an effective preoperative imaging method for the prediction of LN status in VC, allowing the prediction of pathologically negative groins and thus the selection of patients suitable for minimally invasive surgery. Delayed ¹⁸F-FDG PET/CT did not improve the specificity and the positive predictive value in our series. Larger studies are needed for a further validation.

Keywords: 18F-FDG; FDG-retention index; dual time point PET/CT; groin lymph node metastasis; vulvar cancer.