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

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.