Local Tumor Progression after Radiofrequency Ablation of Colorectal Liver Metastases: Evaluation of Ablative Margin and Three-Dimensional Volumetric Analysis

Purpose: Detection of local tumor progression (LTP) after radiofrequency (RF) ablation of colorectal cancer liver metastases may facilitate repeat intervention with potential benefits for patient survival. Ablative margins 1 month after RF ablation may predict LTP, and repeated three-dimensional (3D) volumetric analysis of coagulation volume after ablation may provide earlier detection of LTP versus conventional morphologic criteria. Materials and Methods: Seven patients with LTP and four patients without LTP after a follow-up of at least 24 months were identified. Multidetector computed tomography (CT) was performed at 1 and 3 months after RF ablation and then at 3-month intervals until 24 months. Ablative margins were determined from preablation tumor diameter and the corresponding coagulation diameter 1 month after ablation. Postablation coagulation volume was measured from 81 follow-up multidetector CT images using a seeding-based semiautomatic 3D method. Results: LTP was detected at a median of 9 months (range, 6-21 months) after RF ablation. A coagulation diameter smaller than the preoperative tumor diameter was associated with LTP. Increase in coagulation volume was found in six of seven patients at the time of diagnosis of LTP by conventional morphologic criteria. Conclusion: Three-dimensional volumetric analysis of postablation coagulation volume is feasible for detection of LTP after RF ablation of colorectal cancer liver metastases. No advantage in early detection of LTP was found for 3D volumetric analysis compared with conventional morphologic criteria in this preliminary study. These findings may reflect a type II error caused by the limited sample size.