Evaluation of tumor growth in vivo in a rat model of liver metastasis, using a newly devised index obtained by positron emission tomography with [18F] FDG

Background/Purpose [¹⁸F] fluorodeoxyglucose-positron emission tomography (FDG-PET) is regarded as a unique imaging modality, because the images reflect tumor activity. This characteristic of PET encouraged us to use it to develop a novel method of quantitatively measuring liver metastasis viability. Methods F344 rats were injected with rat colon adenocarcinoma cells (RCN-9 cell line) via the portal vein, and some of them were treated with 5-fluorouracil (5-FU). Tumor growth and tumor activity were measured by PET. We used a tumor viability index (TVI) to evaluate changes in tumor activity and to quantitatively evaluate tumor proliferation activity, instead of using the standardized uptake value (SUV) of the tumor tissue. The TVI was compared with the number of tumor nodules and the proliferating cell nuclear antigen (PCNA) index 28 days after RCN-9 cell inoculation. Results [¹⁸F] FDG uptake by the liver tumors was measured by PET, and the TVI was found to increase as the tumor nodules increased in number and size. The TVI values in the experimental model represented the viability of tumors suppressed by chemotherapy, and the values were significantly correlated with the number of nodules and the PCNA index. Conclusions The TVI was concluded to be superior to the SUV, the commonly used indicator, for evaluating tumor growth, especially that of multiple, small tumors.