Interim Fluorine-18 Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography to Predict Pathologic Response to Preoperative Chemoradiotherapy and Prognosis in Patients With Locally Advanced Rectal Cancer

A pathologic complete response (pCR) to neoadjuvant chemoradiotherapy for rectal cancer has been associated with a better prognosis. To assess the role of interim fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography in the prediction of a pCR and prognosis, we performed a retrospective study. Of the parameters studied, the post-preoperative concurrent chemoradiotherapy maximum standardized uptake value and the change in the maximum standardized uptake value were potent predictors for pCR and well associated with overall survival. Introduction: The goal of the present study was to investigate the predictive and prognostic values of interim fluorine-18 (18F) fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) parameters for the prediction of a complete pathologic response (pCR) in patients with locally advanced rectal cancer (LARC) who had received preoperative chemoradiotherapy (PCRT). Patients and Methods: A total 103 patients with LARC were included in the present study. All the patients were evaluated by 18F FDG PET/CT before and after 45 Gy of radiotherapy with concurrent oral capecitabine chemotherapy. The quantitative, volumetric parameters and their percentage of change (D%) were used to predict the pCR and calculate the overall survival (OS). The predictive value for a pCR of 18F FDG PET/CT cutoff values were determined by receiver operating characteristic analysis. The prognostic significance was assessed using Kaplan-Meier analysis. Results: A pCR occurred in 22 patients (21.4%). Univariate and multivariate analyses demonstrated that the post-PCRT maximum standardized uptake value (SUVmax2) and change in the SUVmax (Delta SUVmax) as significant factors for the prediction of pCR, with a sensitivity of 68.2% and specificity of 87.7% and sensitivity of 90.9% and specificity of 80.3%, respectively. Kaplan-Meier analysis showed that a low SUVmax2 (< 2.5) and high Delta SUVmax (>= 62.2%) were potent predictors for OS. Conclusion: The present study has shown the capability of interim 18F FDG PET/CT parameters to predict the achievement of pCR after PCRT in patients with LARC. Of the parameters, SUVmax2 and Delta SUVmax were potent predictors for pCR and well associated with OS.