Accuracy of MRI and 18F-FDG PET/CT for restaging after preoperative concurrent chemoradiotherapy for rectal cancer

Abstract

Background: Performing a restaging work-up with magnetic resonance imaging (MRI) and (18)F-fluorodeoxyglucose-positron emission tomography/computed tomography ((18)F-FDG PET/CT) can provide information about the effects that are related to preoperative concurrent chemoradiotherapy (CCRT). The purpose of the present study was to investigate the accuracy of MRI and (18)F-FDG PET/CT for restaging after preoperative CCRT for rectal cancer.

Methods: Between April 2005 and February 2006, 30 patients with histologically proven rectal adenocarcinoma were included in this study. Pelvic MRI and (18)F-FDG PET/CT were performed to clinically restage the tumor after CCRT. The results of the pathologic staging were correlated with those of the MRI and (18)F-FDG PET/CT after CCRT. Two patients underwent transanal endoscopic microsurgery after CCRT, and they were excluded when the N category was evaluated.

Results: The overall accuracy of MRI for the T category was 67% (kappa = 0.422, P = 0.003), whereas overstaging and understaging occurred in 30 and 3% of the patients, respectively. For the N category, accurate staging was noted in 75% (kappa = 0.410, P = 0.030) of all the patients, whereas 14% were overstaged and 11% were understaged. The overall accuracy rates for the T and N categories with performing (18)F-FDG PET/CT were 60% (kappa = 0.372, P = 0.004) and 71% (kappa = 0.097, P = 0.549), respectively. While MRI could not predict any patient who showed a pathologic complete response, (18)F-FDG PET/CT predicted three of the four patients who showed a pathologic complete response after preoperative CCRT. Furthermore, (18)F-FDG PET/CT identified distant metastases with an accuracy rate of 97%.

Conclusions: For restaging patients with rectal cancer after preoperative CCRT, MRI is a useful diagnostic modality to predict both the T and N categories. (18)F-FDG PET/CT is helpful in predicting a pathologic complete response and in finding metastasis after preoperative CCRT.