The metabolic response using 18F-fluorodeoxyglucose-positron emission tomography/computed tomography and the change in the carcinoembryonic antigen level for predicting response to pre-operative chemoradiotherapy in patients with rectal cancer.

Abstract

To predict tumor regression in pre-operative chemoradiotherapy (CRT) using (18)F-fluorodeoxyglucose-positron emission tomography/computed tomography (PET/CT) and serum carcinoembryonic antigen (CEA) in patients with rectal cancer. The metabolic response of the tumor was assessed by determining the maximal standardized uptake value (SUV(max)), absolute difference (ΔSUV(max)), and SUV reduction ratio (SRR) on pre- and post-CRT PET/CT scans. The serum CEA, absolute difference (ΔCEA), and the CEA reduction ratio (CRR) were also determined. A receiver-operating characteristic (ROC) curve was generated. Of all seventy two patients, mean pre- and post-CRT SUV(max) was 14.9 and 5.8, respectively. The mean pre- and post-CRT CEA level was 15.5 ng/ml and 5.4 ng/ml, respectively. Forty-three patients (59.8%) were classified as responders (Dworak's tumor regression grade 3-4) and 36 patients (50%) achieved tumor down-staging. ROC analysis showed that both post-CRT SUV(max) and SRR were predictive factors for responders (p=0.03 and p=0.02, respectively). A threshold of post-CRT SUV(max) was 5.4 and that of SRR was 53.1%. Pre-CRT SUV(max), ΔSUV(max), and all parameters in regard to CEA were not significant in ROC analysis. The post-CRT SUV(max) and SRR are potential factors for predicting tumor response in pre-operative CRT. The patients with lower post-CRT SUV(max) and higher SRR could be expected to achieve maximum tumor regression after pre-operative CRT in this study.