Objective: We sought to describe the appearance of primary and secondary lung malignancies treated with radiofrequency ablation on follow-up helical CT and to identify the important CT findings for evaluating therapeutic efficacy and response on follow-up CT.
Materials and methods: Among the 21 patients in our study population, 17 had lung cancer and four had metastatic nodules. All patients underwent follow-up helical CT immediately after undergoing percutaneous radiofrequency ablation, 1 month later, and then every 3 months. Two reviewers interpreted the CT findings and reached a consensus opinion. Patients were divided into two groups on the basis of the posttreatment contrast-enhanced CT findings-those with a complete ablation and those with a partial ablation. The serial changes in the enhancement pattern, size, peripheral ground-glass opacities, and other findings in the treated area in the two groups were assessed on follow-up CT.
Results: In the complete ablation group (n = 9 patients), the ablated lesions were completely without contrast enhancement on follow-up CT, and the mean percentage of decrease in the size of the ablated lesions at 3, 6, 9, 12, and 15 months was 5.7%, 11.4%, 14.3%, 40%, and 40%, respectively, compared with the lesion size on the follow-up CT scans obtained immediately after treatment. In the partial ablation group (n = 12 patients), the ablated lesions had various degrees of enhancement, and the mean percentage of ablated lesion size gradually increased after the 6-month follow-up CT examination. Enveloped ground-glass opacity surrounding tumor was seen in five (23.8%) of 21 lesions on the immediate follow-up CT scans.
Conclusion: Of the CT findings of lung malignancy after radiofrequency ablation therapy, the enhancement pattern and the size of the change in the ablated lesion are the most important factors for determining whether a complete ablation has been achieved.