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The aim of the present study was to compare the tumor volume reduction rate (TVRR), as determined by three-dimensional region-of-interest magnetic resonance volumetry, and Response Evaluation Criteria in Solid Tumors (RECIST) data for predicting the pathological tumor response (PTR) of locally advanced rectal cancer (LARC) following treatment with neoadjuvant chemoradiation (CRT). The current cohort consisted of 105 patients with LARC [clinical tumor stage (cT)3-4 or clinical lymph node stage (cN)+] from a prospective randomized trial who had undergone pre-operative CRT and radical proctectomy. Tumor volumes were measured prior to and following CRT to determine TVRR. Furthermore, receiver operating characteristic (ROC) curves of TVRR and RECIST were constructed to predict the PTR in terms of tumor regression grade (TRG) and downstaging. Values for the area under the ROC curve (AUC) were compared and TVRR cut-off levels were determined. RECIST was used to identify 5 (4.8%) cases of complete response, 44 (41.9%) of partial response, 55 (52.4%) of stable disease and 1 (0.9%) of progressive disease. The mean TVRR was 58.6±24.4%, and a good TRG (0-1) and downstaging occurred in 54 (51.4%) and 59 (56.2%) patients, respectively. In addition, TVRR and RECIST were significantly correlated with TRG and downstaging (P<0.01). The TVRR AUC was significantly larger than that of RECIST for TRG (P=0.020). For downstaging, TVRR also exhibited a larger AUC than RECIST, however, the difference was not significant (P=0.180). The sensitivity and specificity of TVRR in predicting a good TRG were 70.4 and 80.4%, respectively, therefore, the optimal TVRR cut-off value was determined to be 65%. TVRR appeared to be more accurate than RECIST in predicting PTR, particularly for TRG associated with survival. Thus, TVRR may be considered as a novel parameter for evaluating the efficacy of CRT for patients with LARC. [ABSTRACT FROM AUTHOR]