283. 18F-FDG PET/MRI FOR RESTAGING ESOPHAGEAL CANCER AFTER NEOADJUVANT CHEMORADIOTHERAPY

Abstract

Abstract Background The accuracy of 18F-FDG PET/CT is insufficient to detect residual locoregional esophageal cancer after neoadjuvant chemoradiotherapy (nCRT). This feasibility study aims to investigate whether post-treatment 18F-FDG PET/MRI may potentially improve tumor detection. Methods This was a prospective, single center feasibility study. At 6–12 weeks after nCRT, patients underwent standard 18F-FDG PET/CT followed by PET/MRI, and completed a questionnaire to evaluate burden. Two teams of readers either assessed the 18F-FDG PET/CT or the 18F-FDG PET/MRI first; the other scan was assessed one month later. SULmax and ADCmean were measured at the primary tumor location. Histopathology of the surgical resection specimen served as reference standard for diagnostic accuracy calculations. When patients with clinically complete response continued active surveillance, response evaluations until nine months after nCRT served as proxy for ypT and ypN (i.e. ‘ycT’, ‘ycN’). Results In the 21 included patients (median age 70 [IQR 62–75], 16 males), disease recurrence was found in the primary tumor in 14 (67%) patients (of whom one ypM+, detected on both scans), and in locoregional lymph nodes in six patients (29%). Accuracy (team 1/team 2) to detect yp/ycT+ with 18F-FDG PET/MRI vs 18F-FDG PET/CT was 38/57% vs 76/61%. For ypN+, accuracy was 63/53% vs 63/42%, resp. Neither SULmax (both scans) nor ADCmean were discriminatory for yp/ycT+. Fourteen of 21 (67%) patients were willing to undergo a similar 18F-FDG PET/MRI examination in the future. Conclusion 18F-FDG PET/MRI currently performs comparably to 18F-FDG PET/CT. Improvements in the scanning protocol, increasing reader experience, and performing serial scans might contribute to enhance accuracy of tumor detection after nCRT using 18F-FDG PET/MRI.