title: 18F-FDG small-animal PET for monitoring the therapeutic effect of CT-guided radiofrequency ablation on implanted VX2 lung tumors in rabbits.
abstract: 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.
authors.affiliation: Department of Radiology, Osaka City University Graduate School of Medicine, Osaka, Japan. o-kuma@msic.med.osaka-cu.ac.jp
authors.forename: Tomohisa
authors.initials: T
authors.lastname: Okuma
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Matsuoka
authors.forename: Terue
authors.initials: T
authors.lastname: Okamura
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Wada
authors.forename: Akira
authors.initials: A
authors.lastname: Yamamoto
authors.forename: Yoshimasa
authors.initials: Y
authors.lastname: Oyama
authors.forename: Koichi
authors.initials: K
authors.lastname: Koyama
authors.forename: Kenji
authors.initials: K
authors.lastname: Nakamura
authors.forename: Yasuyoshi
authors.initials: Y
authors.lastname: Watanabe
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Inoue
mesh_terms: 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
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18