Objective: The performance of microPET using 18F-FDG was evaluated in a rabbit model of hematogenous pulmonary metastatic cancer.
Methods: A total of 15 Japanese white rabbits and VX-2 carcinoma were used in this study. In the microPET study, tumor-bearing rabbits were administered intravenously 74 MBq of 18F-FDG, and 30 min later, the emission data were acquired for 60 min. The transmission scans were performed with a 68Ge/68Ga external point source. To augment the anatomical information, we performed multi-detector row computed tomography (MDCT) in the combination with MDCT and microPET on 10 rabbits. The other 5 rabbits were followed once a week for 5 weeks only by microPET. Tumor/muscle (T/M) ratios were used for quantitative evaluation in this study.
Results: Multiple pulmonary nodules were detected by MDCT and microPET starting 14 days after the tumor injection. The high-uptake lesions in the lung detected by microPET corresponded well to the tumors detected by MDCT. The smallest nodule detected by microPET was ca. 1.5 mm in diameter. Overall, 87 nodules were detected by MDCT and the ratios of lesions detected by microPET to those by MDCT were 35.3%, 77.5%, and 90% for tumors equal to or smaller than 2 mm, 2-4 mm, and 4-6 mm in diameter, respectively. The respective T/M ratios were 2.41 +/- 0.41, 2.93 +/- 0.55, and 3.34 +/- 0.71. The T/M ratio increased with tumor size, but it was similar in each tumor size category. In the 35-day follow-up protocol, it was possible to follow sequentially the same tumor by the microPET.
Conclusions: By FDG-microPET, it is possible to evaluate tumors larger than 2 mm in diameter and to follow the growth of individual tumors. Our results also suggest that the rabbit model of VX-2 pulmonary metastasis is a stable experimental model for evaluation using FDG. Monitoring of the therapeutic effects of anticancer drugs and radiation therapy could be tried by using this model and microPET.