• Young Chul Kim, Joon Seok Lim, Ki Chang Keum, Kyung Ah Kim, Sungmin Myoung, Sang Joon Shin, Myeong-Jin Kim, Nam Kyu Kim, Jinsuk Suh, and Ki Whang Kim.
• Department of Radiology, Research Institute of Radiological Science, Yonsei University Health System, Seoul, Republic of Korea.
• J Magn Reson Imaging. 2011 Sep 1; 34 (3): 570-6.

PurposeTo compare diffusion-weighted imaging (DWI) and magnetic resonance (MR) volumetry for predicting treatment outcomes of locally advanced rectal cancers with preoperative chemoradiotherapy (CRT).Materials And MethodsThis prospective study was approved by our Institutional Review Board. Thirty-four patients underwent three MR examinations: pre-CRT (before CRT), early CRT (2 weeks after CRT initiation), and post-CRT (before surgery). The tumor apparent diffusion coefficient (ADC), ADC increase rate, and volume reduction rate were compared between responders and nonresponders using three reference standards: downstaging, modified Response Evaluation Criteria in Solid Tumors (mRECIST), and tumor regression grade (TRG). For DWI and volumetry, differences between responders and nonresponders were assessed by receiver operating characteristic analysis.ResultsThe median early tumor volume reduction rate of responders, subgrouped by downstaging and mRECIST (47.97% and 53.97%, respectively), was significantly higher than that of nonresponders (20.94% and 20.36%; P = 0.0024 and 0.0001, respectively), but there were no significant differences in pre-CRT ADC and early ADC increase rate using all references. When using the downstaging and mRECIST, the diagnostic performance of early tumor volume reduction rate (Az = 0.81 and 0.94, respectively) was higher than that of pre-CRT ADC (Az = 0.55 and 0.62; P = 0.033 and 0.007) and early ADC increase rate (Az = 0.58 and 0.64; P = 0.055 and 0.01) for predicting the treatment outcome. For TRG, there were no significant differences between DWI and volumetry.ConclusionEarly tumor volume reduction rate at the second week after CRT initiation may be a better indicator than DWI based on the mean ADC measurements for predicting CRT treatment outcome.Copyright © 2011 Wiley-Liss, Inc.

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