18F-FDG small-animal PET for monitoring the therapeutic effect of CT-guided radiofrequency ablation on implanted VX2 lung tumors in rabbits.
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).


CONCLUSIONS
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.
Okuma
Tomohisa
T
Department of Radiology, Osaka City University Graduate School of Medicine, Osaka, Japan. o-kuma@msic.med.osaka-cu.ac.jp
Matsuoka
Toshiyuki
T
Okamura
Terue
T
Wada
Yasuhiro
Y
Yamamoto
Akira
A
Oyama
Yoshimasa
Y
Koyama
Koichi
K
Nakamura
Kenji
K
Watanabe
Yasuyoshi
Y
Inoue
Yuichi
Y
D000818:Animals; D002277:Carcinoma / Q000473:pathology; D017115:Catheter Ablation; D004195:Disease Models, Animal; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007249:Inflammation; D008168:Lung / Q000473:pathology; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000628:therapy*; D009368:Neoplasm Transplantation; D049268:Positron-Emission Tomography / Q000379:methods*; D011817:Rabbits; D019275:Radiopharmaceuticals; D013997:Time Factors; D014057:Tomography, X-Ray Computed
D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18