FDG-PET EVALUATION OF THERAPEUTIC EFFECTS ON VX2 LIVER-TUMOR

Transplanted VX2 liver tumor in the rabbit is an experimental liver tu mor model in which F-18-2-fluoro-2-deoxy-D-glucose (FDG) accumulates t o a 3.5-fold level that surrounds normal liver tissue. In this study, changes in FDG uptake were assessed in this liver tumor model after tr anscatheter arterial embolization (TAE) and radiotherapy. Methods: Fif teen rabbits bearing VX2 liver tumors were treated with TAE with gelat in sponges 1 day before the FDG study, and 18 rabbits received local i rradiation with electron beams at a dose of 12-36 Gy 1-10 days before the FDG study. In the FDG study, serial arterial blood sampling was pe rformed to determine arterial input (Al), and 1 hr after tracer inject ion, normal liver tissue and tumor tissue were excised to measure radi oactivity. The tumor FDG level per Al and the tumor-to-normal liver ra tio were assessed. Dynamic PET images were obtained in 20 of the 46 ra bbits. Results: Tumor FDG uptake was significantly decreased 1 day aft er TAE (from 3.54 to 0.83 in the tumor-to-normal liver ratio) and 5 da ys after 30 Gy of irradiation (from 3.54 to 1.28). The decrease in tum or FDG uptake was dose-dependent, especially in the relatively low dos e range (12-24 Gy). The untreated tumors could be clearly distinguishe d from the surrounding normal liver tissue, while the embolized tumors or the irradiated tumors were not clearly delineated. Histological an alysis showed that the decrease in tumor FDG after treatment agreed we ll with the decrease in number of viable tumor cells. Conclusion: The VX2 liver tumor is an appropriate experimental tumor model For evaluat ing the change in FDG uptake in various therapeutic modalities. Moreov er, the therapeutic effects can be assessed 1 day after TAE and 5 days after irradiation. Further clinical trials for the early evaluation o f therapeutic effects on liver tumors using FDG-PET are warranted.