Three-dimensional Radiologic Assessment of Chemotherapy Response in ă Ewing Sarcoma Can Be Used to Predict Clinical Outcome

Purpose: To compare the agreement of three-dimensional (3D) tumor ă measurements for therapeutic response assessment of Ewing sarcoma ă according to the Children's Oncology Group (COG) criteria, ă one-dimensional (1D) Response Evaluation Criteria in Solid Tumors ă (RECIST), and two-dimensional (2D) measurements defined by the World ă Health Organization (WHO) with tumor volume measurements as the standard ă of reference and to determine which method correlates best with clinical ă outcomes. ă Materials and Methods: This retrospective study was approved by the ă institutional review board of three institutions. Seventy-four patients ă (mean age +/- standard deviation, 14.5 years +/- 6.5) with newly ă diagnosed Ewing sarcoma treated at three medical centers were evaluated. ă Primary tumor size was assessed on pre-and posttreatment magnetic ă resonance images according to 1D RECIST, 2D WHO, and 3D COG ă measurements. Tumor responses were compared with the standard of ă reference (tumor volume) on the basis of RECIST, COG, and WHO ă therapeutic response thresholds. Agreement between the percentage ă reduction measurements of the methods was assessed with concordance ă correlation, Bland-Altman analysis, and Spearman rank correlation. ă Agreement between therapeutic responses was assessed with Kendall tau ă and unweighted kappa statistics. Tumor responses were compared with ă patient survival by using the log-rank test, Kaplan-Meier plots, and Cox ă regression. ă Results: Agreement with the reference standard was significantly better ă for 3D measurement than for 1D and 2D measurements on the basis of ă RECIST and COG therapeutic response thresholds (concordance correlation ă of 0.41, 0.72, and 0.84 for 1D, 2D, and 3D measurements, respectively; P ă