The metabolic response using F-18-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

Background and purpose: To predict tumor regression in pre-operative chemoradiotherapy (CRT) using F-18-fluorodeoxyglucose-positron emission tomography/computed tomography (PET/CT) and serum carcinoembryonic antigen (CEA) in patients with rectal cancer. Materials and methods: The metabolic response of the tumor was assessed by determining the maximal standardized uptake value (SUVmax), absolute difference (Delta SUVmax), and SUV reduction ratio (SRR) on pre- and post-CRT PET/CT scans. The serum CEA, absolute difference (Delta CEA), and the CEA reduction ratio (CRR) were also determined. A receiver-operating characteristic (ROC) curve was generated. Results: Of all seventy two patients, mean pre- and post-CRT SUVmax 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 SUVmax and SRR were predictive factors for responders (p = 0.03 and p = 0.02, respectively). A threshold of post-CRT SUVmax was 5.4 and that of SRR was 53.1%. Pre-CRT SUVmax, Delta SUVmax, and all parameters in regard to CEA were not significant in ROC analysis. Conclusions: The post-CRT SUVmax and SRR are potential factors for predicting tumor response in pre-operative CRT. The patients with lower post-CRT SUVmax and higher SRR could be expected to achieve maximum tumor regression after pre-operative CRT in this study. (C) 2010 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 98 (2011) 134-138