TUMOR VOLUME CHANGES ASSESSED BY THREE-DIMENSIONAL MAGNETIC RESONANCE VOLUMETRY IN RECTAL CANCER PATIENTS AFTER PREOPERATIVE CHEMORADIATION: THE IMPACT OF THE VOLUME REDUCTION RATIO ON THE PREDICTION OF PATHOLOGIC COMPLETE RESPONSE

Purpose: The aim of this study was to determine the correlation between tumor volume changes assessed by three-dimensional (3D) magnetic resonance (MR) volumetry and the histopathologic tumor response in rectal cancer patients undergoing preoperative chemoradiation therapy (CRT). Methods and Materials: A total of 84 patients who underwent preoperative CRT followed by radical surgery were prospectively enrolled in the study. The post-treatment tumor volume and tumor volume reduction ratio (% decrease ratio), as shown by 3D MR volumetry, were compared with the histopathologic response, as shown by T and N downstaging and the tumor regression grade (TRG). Results: There were no significant differences in the post-treatment tumor volume and the volume reduction ratio shown by 3D MR volumetry with respect to T and N downstaging and the tumor regression grade. In a multivariate analysis, the tumor volume reduction ratio was not significantly associated with T and N downstaging. The volume reduction ratio (>75%,p = 0.01) and the pretreatment carcinoembryonic antigen level (<= 3 ng/ml,p = 0.01), but not the post-treatment volume shown by 3D MR (<= 5ml), were, however, significantly associated with an increased pathologic complete response rate. Conclusion: More than 75% of the tumor volume reduction ratios were significantly associated with a high pathologic complete response rate. Therefore, limited treatment options such as local excision or simple observation might be considered after preoperative CRT in this patient population. (C) 2010 Elsevier Inc.