Threshold of maxSUV and SUV reduction rate in detection of remnant malignancy after preoperative chemoradiation therapy in patients with rectal cancer

1209 Objectives The purpose of our study is to determine the threshold of maxSUV and SUV reduction ratio in detecting remnant malignancy after preoperative chemoradiation therapy (CRT) in rectal cancer. Methods Rectal cancer patients (n=25) who underwent F-18 FDG PET/CT (PET/CT) before and after CRT were included. All of them underwent operation after second PET/CT. The mean time interval from CRT to PET was 35.4 ± 6.2 days. Complete regression and remnant malignancy groups were pathologically determined after surgery. The threshold of maxSUV (on PET after preoperative CRT) and SSR (SUV reduction ratio = (staging SUV-restaging SUV)/staging SUV]) were measured by the areas under the ROC curve. Results Complete remissions were showed in four patients. Twenty-one patients had remnant malignancies on operation. For detecting remnant malignancy, maxSUV threshold of >4 showed sensitivity 66.7%, specificity 100%, positive predictive value 100% and negative predictive value 36.4% (p=0.0031). However, SSR dose not show an ability to distinguish between complete remission and remnant lesions (p=0.77). Conclusions In restaging PET/CT after preoperative CRT in rectal cancer, maxSUV threshold over 4 can be used to determine remnant malignancy