Efficacy of Preoperative Combined 18-Fluorodeoxyglucose Positron Emission Tomography and Computed Tomography for Assessing Primary Rectal Cancer Response to Neoadjuvant Therapy

Purpose Efficacy of F-18 fluorodeoxyglucose positron emission tomography combined with computed tomography (FDG-PET/CT) for determining neoadjuvant therapy response in rectal cancer is not well established. We sought to evaluate serial FDG-PET/CT for assessing tumor down-staging, percentage residual tumor, and complete response or microscopic disease with rectal cancer neoadjuvant therapy. Methods Patients with rectal cancer undergoing neoadjuvant therapy, definitive surgical resection, and FDG-PET/CT before and 4–6 weeks after neoadjuvant treatment were included. Tumors were evaluated pretreatment and on final pathology for size and stage. FDG-PET/CT parameters assessed were visual response score (VRS), standardized uptake value (SUV), PET-derived tumor volume (PETvol), CT-derived tumor volume (CTvol), and total lesion glycolysis (δTLG). Results Twenty-one rectal cancer patients over 3 years underwent neoadjuvant treatment, serial FDG-PET/CT, and resection. Complete response or microscopic disease (n = 7, 33%) was associated with higher ΔCTvol (AUC = 0.82, p = 0.004) and ΔSUV (AUC = 0.79, p = 0.01). Tumor down-staging (n = 14, 67%) was associated with greater ΔPETvol (AUC = 0.82, p < 0.001) and ΔSUV (AUC = 0.82, p < 0.001). Pathologic lymph node disease (n = 7, 33%) correlated with ΔCTvol (AUC = 0.75, p = 0.03) and ΔPETvol (AUC = 0.70, p = 0.08). Conclusion FDG-PET/CT parameters were best for assessing tumor down-staging and percentage of residual tumor after neoadjuvant treatment of rectal cancer and can potentially assist in treatment planning. This work was presented in the plenary session of the 47th Annual Meeting of the Society for Surgery of the Alimentary Tract at the Digestive Disease Week in Los Angeles, CA on 24 May 2006.