18F-FDG Small-Animal PET for Monitoring the Therapeutic Effect of CT-Guided Radiofrequency Ablation on Implanted VX2 Lung Tumors in Rabbits

摘要

id="p-1">The primary goals of this study were to investigate the behavior of normal lung tissues after radiofrequency ablation (RFA) and to determine the suitability of 18F-FDG PET, using a dedicated small-animal scanner, for monitoring the early therapeutic effects of RFA on VX2 lung tumors (VX2s) in rabbits. >Methods: Fourteen Japanese white rabbits with normal lungs underwent RFA, followed by 18F-FDG PET at 1 d and at 1, 2, 4, and 8 wk. In addition, 7 rabbits with untreated VX2s underwent 18F-FDG PET, and 13 rabbits with RFA-treated VX2s underwent 18F-FDG PET at 1 d (n = 7) or 1 wk (n = 6) after the treatment. >Results: After RFA of normal lungs, ring-shaped accumulations of 18F-FDG, which coincided with inflammation caused by ablation, were observed. The mean early- (40-60 min after injection) and delayed (100-120 min)-phase ablated lesion-to-muscle ratios were, respectively, 2.9 ?± 1.0 and 3.3 ?± 0.8 (1 d), 4.1 ?± 0.6 and 5.2 ?± 0.9 (1 wk), 4.1 ?± 1.0 and 5.3 ?± 1.5 (2 wk), 3.1 ?± 0.5 and 3.6 ?± 1.1 (4 wk), and 1.8 ?± 0.1 and 2.3 ?± 0.1 (8 wk). At 4 and 8 wk, the uptake was less than that at 1 and 2 wk (P 0.05). VX2s showed mean tumor-to-muscle ratios of 6.6 ?± 2.1 and 8.6 ?± 3.3 at the early and delayed phases, respectively. For ablated tumors, the respective ratios were 0.8 ?± 0.4 and 1.1 ?± 0.7 (1 d) and 1.2 ?± 0.5 and 1.5 ?± 0.7 (1 wk). These values were significantly lower than those for nonablated tumors (P 0.001). Histopathologic examination confirmed the absence of viable tumors. 18F-FDG accumulation around ablated tumors reflected thermally damaged normal tissues and was significantly lower than that of control VX2s (P 0.01). >Conclusion: Our data suggest that 18F-FDG PET is promising for evaluating the therapeutic response of lung malignancies to RFA: Accumulation of 18F-FDG in surrounding normal tissues appears to be time dependent, and the data suggest that, clinically, 18F-FDG PET should be performed 4 wk or more after RFA. Delayed-phase images seem to better distinguish tumor from inflammation than do early-phase images.