Background: Thermal ablation is becoming an increasingly utilized treatment modality for medically inoperable lung cancer patients. Assessing treatment response with non-invasive means is important as retreatment with ablation or radiotherapy is often possible. The purpose of our study was to analyze the FDG-PET studies pre- and post-ablation in order to find qualitative or quantitative measures of treatment success.

Methods: 38 patients who underwent thermal ablation with either radiofrequency (RFA) or microwave (MWA) for NSCLC (22 males, 16 females; average age 75) between 6/2003 and 9/2006 had FDG-PET scans on average 2 months prior and 7 months after ablation were retrospectively analyzed. Quantitative and qualitative analysis of the FDG-PET studies was performed by two board certified radiologists with experience in PET and board certification in nuclear medicine. Quantitative analysis of PET imaging features was performed by measuring the maximum standardized uptake value (SUV) prior to and after ablation. These results were compared with clinical outcomes.

Results: The SUV of NSCLC prior to RFA or MWA did not predict treatment response. The mean (range) SUV for all ablations pre- and post-PET was 6.5(1.3-17.7) and 4.0 (0.8-20.1), respectively.10/38 neoplasms had increased SUV after ablation and 28/38 neoplasms had a decrease in the SUV. Mean post-PET SUVs were not signifiantly different between RFA and MWA; MW alone (15 neoplasms, pre/post-SUV 6.1/3.7 ; RFA alone (23 neoplasms, pre/post-SUV 6.9/4.0). There were 14 known recurrences which exhibited higher than average post-PET SUV when compared to their stable counterparts. Recurrences had an average pre/post-PET SUV of 6.8/6.1, compared to their stable counterparts 6.1/2.8. Furthermore, 70% of patients with recurrences had increased SUV on post-PET ablation scans compared to 25% in patients who had an interval decrease in post-PET ablation SUV. Qualitatively post-ablation neoplasms exhibiting central photopenia with homogenous rim uptake similar to or less than medistinal background activity post ablation appear to be associated with disease stability. Of ten neoplasms that exhibited this radiographic feature only 1 recurred.

Conclusions: Post-ablation FDG-PET SUV and imaging features may be useful in assessing treatment response after thermal ablation.