Radiofrequency ablation of medically inoperable stage IA non-small cell lung cancer: are early posttreatment PET findings predictive of treatment outcome?

Abstract

Objective: The purpose of this study was to evaluate initial experience with (18)F-FDG PET/CT after pulmonary radiofrequency ablation of stage IA non-small cell lung cancer to determine whether treatment success or residual disease can be predicted with early postablation PET.

Subjects and methods: Thirty patients with medically inoperable stage IA non-small cell lung cancer (12 men, 18 women; median age, 76 years; range, 60-87 years) underwent outpatient CT-guided radiofrequency ablation over a 33-month period. Mean tumor size was 2.0 cm (range, 1.3-2.9 cm). PET/CT was performed within 60 days before radiofrequency ablation (RFA), within 4 days after RFA, and 6 months after RFA. Metabolic response was categorized as complete response or partial or no response at early post-RFA PET/CT and complete response, partial response, or progressive metabolic disease at 6-month post-RFA PET/CT and was compared with the 1-year clinical event rate (death, disease progression at contrast-enhanced CT, or repeat ablation).

Results: Early PET/CT images, obtained within 4 days of RFA, were evaluable for 26 patients (23 at 6 months). Patients with a complete metabolic response at early PET/CT had a 1-year event rate of 43%, whereas those with partial or no response or disease progression had a 1-year event rate of 67% (p = 0.27). Patients with a complete metabolic response at 6-month PET/CT had a 1-year event rate of 0%. Those with a partial response and those with disease progression had an overall event rate of 75% (p = 0.001).

Conclusion: Early post-RFA PET/CT is not necessary and 6-month post-RFA PET/CT findings correlate better with clinical outcome at 1 year.

Fig. 1

Standards for Reporting of Diagnostic Accuracy diagram shows numbers of patients in PET substudy cohort undergoing PET/CT 1–4 days and 6 months after RFA.

Fig. 2

66-year-old woman with stage IA non–small cell lung cancer. A–C, Axial PET (A), CT (B), and fused PET/CT (C) images obtained before radiofrequency ablation (RFA) show area of intense FDG uptake corresponding to tumor in right upper lobe. D–F, Axial PET (D), CT (E), and fused PET/CT (F) images obtained 3 days after RFA show homogeneous rim activity along periphery of ablation site with central photopenia (complete response). Rim activity is higher than background mediastinal activity. G–I, Axial PET (G), CT (H), and fused PET/CT (I) images 6 months after RFA no longer show homogeneous rim activity. Mild linear FDG uptake at ablation site has intensity similar to mediastinal blood pool activity (complete response).

Fig. 3

85-year-old woman with stage IA non–small cell lung cancer. A–C, Axial PET (A), CT (B), and fused PET/CT (C) images obtained before radiofrequency ablation (RFA) show area of intense FDG uptake in left upper lobe. D–F, Axial PET (D), CT (E), and fused PET/CT (F) images obtained 4 days after RFA show discrete focus of intense activity at medial margin of ablation site corresponding to opacity with irregular margins (arrow) (partial response). G–I, Axial PET (G), CT (H), and fused PET/CT (I) images obtained 6 months after RFA images show minimal homogeneous rim activity with complete interval resolution of intense focus of increased activity in D–F (complete response).

Fig. 4

87-year-old woman with stage IA non–small cell lung cancer. A–C, Axial PET (A), CT (B), and fused PET/CT (C) images show area of intense FDG uptake corresponding to tumor in right upper lobe. D–F, Axial PET (D), CT (E), and fused PET/CT (F) images obtained 3 days after radiofrequency ablation (RFA) show more discrete focus of increased activity (arrow, D) at medial aspect of ablation site (partial response). Ablation site otherwise exhibits mild peripheral uptake and central photopenia. G–I, Axial PET (G), CT (H), and fused PET/CT (I) images obtained 6 month after RFA show persistent and slightly more intense discrete focus of increased activity (arrow, G) at medial portion of ablation site corresponding to small nodular opacity at posterome-dial aspect of triangular ablation cavity (progressive disease). J, Axial CT densitometry image obtained 6 months after RFA shows enhancement of nodular focus at medial aspect of ablation cavity (arrow) that corresponds to location of discrete focal activity in D–I.