The role of sequential 18F-FDG PET/CT in predicting tumour response after preoperative chemoradiation for rectal cancer

Aim The aim of this study was to investigate the potential of sequential positron emission tomography (PET)/CT standardized uptake value (SUV)/metabolic area variation in predicting the pathological response to preoperative chemoradiotherapy (CRT) for rectal cancer. Method Fifty-three patients diagnosed with clinical T3-4 and/or N+ rectal cancer were enrolled. All patients received CRT followed by radical surgery after 68weeks. A PET/CT scan was performed before (PET/CT1) initiation of treatment and a second scan (PET/CT2) was performed within 1week after the completion of CRT. Thirty-five of 53 patients also underwent a third (PET/CT3) scan within 1week before surgery. Maximal SUV within the tumour (SUVmax), average SUV within the tumour (SUVmean), metabolic tumour volume (MV), total lesion glycolysis (TLG) and response indices (%, i.e. the percentage difference between two different PET/CT scans for SUVmax, SUVmean, MV and TLG) were calculated. The different metabolic parameters were analysed and correlated with the tumour regression grade (TRG) score. Results When patients were regrouped as responders (TRG 3-4) and nonresponders (TRG 0-2), significant differences were observed in the percentage differences between PET/CT1 and PET/CT3 for MV (%MV(1-3); 91.08% vs 75.43%) and for TLG (%TLG(1-3); 94.00% vs 82.02%). As demonstrated by receiveroperating characteristics analysis, %MV(1-3) and %TLG(1-3) both had a strong capability to discriminate between responders and nonresponders. Patients classified as having a pathological complete response (pCR) and a non-pCR showed significant differences in the percentage difference between PET/CT1 and PET/CT3 in SUVmax (% SUVmax(1-3); 69.17% vs 57.77%), SUVmean (% SUVmean(1-3); 44.20% vs 30.19%), %MV(1-3) (90.93% vs 80.30%) and %TLG(1-3) (94.22% vs 85.63%). %TLG (1-3) was a more powerful discriminator than the others. Conclusion Differences in the SUV/metabolic area with 18F-fluorodeoxyglucose (18F-FDG) PET/CT have the potential to predict a response to preoperative CRT for rectal cancer.