Tumor compactness improves the preoperative volumetry-based prediction of the pathological complete response of rectal cancer after preoperative concurrent chemoradiotherapy

// Che-Yu Hsu 1 , Chun-Wei Wang 2, 4 , Chia-Chun Kuo 3 , Yu-Hsuan Chen 2, 4 , Keng-Hsueh Lan 2, 4 , Ann-Lii Cheng 4, 5, 6 , Sung-Hsin Kuo 2, 4, 5, 6 1 Division of Radiation Oncology, Department of Oncology, National Taiwan University Hospital Yun-Lin Branch, Yunlin, Taiwan 2 Division of Radiation Oncology, Department of Oncology, National Taiwan University Hospital and National Taiwan University Cancer Center, Taipei, Taiwan 3 Division of Radiation Oncology, Department of Oncology, Taiwan Medical University Hospital, Taipei, Taiwan 4 National Taiwan University Cancer Center, National Taiwan University College of Medicine, Taipei, Taiwan 5 Cancer Research Center, National Taiwan University College of Medicine, Taipei, Taiwan 6 Graduate Institute of Oncology, National Taiwan University College of Medicine, Taipei, Taiwan Correspondence to: Sung-Hsin Kuo, email: shkuo101@ntu.edu.tw Keywords: rectal cancer, tumor compactness, pathologic complete remission, preoperative, chemoradiotherapy Received: March 30, 2016 Accepted: November 21, 2016 Published: December 10, 2016 ABSTRACT In addition to clinical factors (tumor and node stage) and treatment factors (equivalent radiotherapy dose and chemotherapy regimen), we assessed whether different performances of various tumor volume measurements help predict the pathological complete response (pCR) of locally advanced rectal cancer (LARC) after preoperative concurrent chemoradiotherapy (CCRT). A total of 122 patients with LARC treated with a long course of CCRT, between December 2009 and March 2015, were enrolled in this bi-institutional study. Tumor delineation was based on standard T2-weighted magnetic resonance imaging or contrast-enhanced computed tomography before CCRT. Tumor compactness was defined as the ratio of the volume and the surface area. The tumor compactness-corrected TV (TCTV) was defined as the ratio of the real TV (RTV) and tumor compactness. Twenty-three (18.9%) patients had a pCR. Areas under the curve of the receiver operating characteristic for pCR prediction calculated using the RTV, cylindrical approximated TV (CATV), and TCTV were 0.724, 0.747, and 0.780, respectively. The prediction performance of TCTV was significantly more efficient than that of both RTV ( P = 0.0057) and CATV ( P = 0.0329). Multivariate logistic regression analysis revealed tumor compactness ( P = 0.001), RTV ( P = 0.042), and preoperative clinical nodal status ( P = 0.044) as significant predictors of a pCR. In addition, poor tumor compactness was closely associated with lymphovascular space invasion ( P = 0.008) and pathological nodal status ( P = 0.003). For patients with LARC receiving preoperative CCRT, tumor compactness is a useful radiomic parameter for improving the volumetric based prediction model.