Early indicators of treatment success after percutaneous radiofrequency of pulmonary tumors.

We retrospectively reviewed the imaging of patients after radiofrequency ablation (RFA) of lung metastases performed at our institution to assess the usefulness of ground glass opacification (GGO) margin for the prediction of complete tumor ablation. From January 2004 to March 2007, patients were identified where there was a postprocedure thin collimation scan to allow multiplanar reformatting, either immediately or at 24 h and at least 6 months of imaging follow-up. Thirty-six tumors in 22 patients were identified. The scans were assessed for the presence and width of GGO margin, and minimal and maximal dimensions were measured. A second reviewer, blinded to the outcome of the postprocedure assessment, reviewed the follow-up imaging for recurrence. The recurrence group had larger tumors (p = 0.045) and smaller mean minimal GGO margin width (p = 0.0001). Multivariate binary regression analysis confirmed that the minimal GGO margin was significantly (p < 0.005) associated with tumor recurrence. Receiver operator characteristic curve analysis suggests a cutoff of 4.5 mm for complete tumor ablation. There was substantial agreement (kappa = 0.759) between the site of absent GGO margin and the site of tumor recurrence. The point on the tumor surface where there is no GGO margin is likely to be the site of future recurrence. In our experience, a circumferential GGO margin of >5 mm is the minimal margion required to ensure complete tumor ablation.