Postablation signs predict successful lung RFA

A lesion's contrast enhancement pattern and change in size after treatment can predict the successful radio-frequency ablation of a lung tumor, according to a study in the October issue of the American Journal of Roentgenology.

Dr. Gong Yong Jin and colleagues at Chonbuk and Seoul National University Hospitals in Korea retrospectively evaluated 21 patients who underwent percutaneous RFA for lung cancer and metastases from extrapulmonary lesions. Using contrast-enhanced CT, they sought to describe postablation lesion characteristics and patient response to treatment.

The researchers found that the most successfully ablated lesions appeared on follow-up scans as low-attenuation areas without contrast enhancement. These lesions consistently shrank on subsequent follow-up scans.

Based on contrast-enhanced CT findings after treatment, the researchers split patients into two groups: those who had achieved complete ablation, and those with a partial ablation. Follow-up CT imaging of each group showed serial changes in enhancement patterns, size, peripheral ground-glass opacities, and other factors.

Nine patients in the complete ablation group showed no contrast enhancement on follow-up CT. Their lesions' mean reduction rate at three, six, nine, 12, and 15 months compared with the size right after treatment was 5.7%, 11.4%, 14.3%, 40%, and 40%, respectively.

Twelve patients in the partial ablation group showed diverse degrees of enhancement. In contrast to the previous group, their lesions gradually increased in size after the six-month follow-up with CT. Five out of 21 lesions on postablation scans showed enveloped ground-glass opacity surrounding the tumor.

Usually, a brief increase in blood flow occurs along the tissue surrounding an ablated lesion. Experts speculate that residual malignant cells overlapping this area might go undetected by follow-up CT immediately after treatment. Ablation should thus include a peripheral normal tissue margin of .5 to 1 cm to boost results and increase the sensitivity of treatment follow-up.

Lack of histopathologic confirmation limited the study's measure for success. Several other researchers, however, agree that contrast-enhanced CT findings may correlate well with the ablated lesion's pathologic features, the investigators wrote in the study.

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