The role of [18F]FDG PET/CT in pulmonary microwave ablation

Introduction: As the population ages, an increasing number of patients cannot afford surgery because of comorbidities. Consequently, in the last two decades numerous techniques for local treatment have been developed. Microwave ablation (MWA) presents several advantages, such as higher temperatures, larger ablation volumes, shorter ablation times, and less intra-procedural pain. Today, [¹⁸F]FDG PET/CT is continually applied in clinical oncology routine for assessing treatment response.

The purpose of our study was to retrospectively evaluate whether semi-quantitative and volumetric parameters from [¹⁸F]FDG PET/CT could be associated with clinical outcomes in patients with pulmonary lesions treated with MWA.

Methods: Between January 2013 and December 2023, 40 patients (26 male, 14 female, mean age 76 years) underwent MWA in our hospital (Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan). [¹⁸F]FDG PET/CT was performed before and after a median of 3 ± 3 months (median ± IQR; range: 1-17 months) from procedure. For each lesion we semi-automatically calculated SUVmax, SUVmean, total lesion glycolysis (TLG), and metabolic tumor volume (MTV), as well as their percentage of change (Δ) using Syngo-via software. Progression-free survival (PFS) and overall survival (OS) were determined and compared using the Kaplan-Meier and the log-rank test. The median follow-up was 76 months (95% CI: 42-109 months).

Results: Overall 50 pulmonary lesions, primary lung cancers (n=41) and metastases (n=9), were treated with MWA. The mean maximal axial diameter of lesions was 16.4 ± 6.97 mm (mean ± SD; range: 5–35 mm). The median hospital length of stay was of 2 ± 2 days (median ± IQR; range: 1-7). The complication rate was 40%: pneumothorax (n=15), pulmonary hemorrhage (n=2), pneumonia (n=2), and pleural effusion (n=1), while no adverse events occurred in 25 (62.5%) patients.

Patients with median SUVmax after MWA lower than 2.53 and those with median ΔSUVmean lower than -4.17% showed longer PFS (p=0.02 and p=0.021, respectively). Likewise, median SUVmax and median SUVmean after MWA, as well as median ΔSUVmean were significantly associated with OS (p=0.038, p=0.037, and p=0.02, rispectively) (Figure 1), whereas median SUVmax at baseline showed only a tendency (p=0.06). On the other hand, volumetric parameters, expressed by TLG and MTV, were not prognostic neither for PFS nor for OS.

Conclusions: Our preliminary results showed that the metabolic activity, at the first evaluation after MWA, was correlated with PFS and OS. SUVs parameters can be a potentially valuable tools for identifying patients who are likely to benefit from MWA.

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