Diffusion-weighted MRI and 18F-FDG PET correlation with immunity in early radiotherapy response in BNL hepatocellular carcinoma mouse model: timeline validation

PurposeImaging probes/biomarkers that are correlated with molecular or microenvironmental alterations in tumors have been used not only in diagnosing cancer but also in assessing the efficacy of cancer treatment. We evaluated the early response of hepatocellular carcinoma (HCC) to radiation treatment using T2-weighted magnetic resonance imaging (MRI), diffusion-weighted (DW) MRI, and F-18-fluorodeoxyglucose (F-18-FDG) positron emission tomography (PET).MethodsOrthotopic HCC tumors were established in the right liver lobe of Balb/c mice. Mice were longitudinally scanned using T2-weighted/DW MRI and F-18-FDG PET 1day before and on days 1, 3, 6, 9 and 13 after irradiation with 15Gy to the right liver lobe to determine tumor size, apparent diffusion coefficient (ADC) value, and maximum standardized uptake value. Immunohistochemical (IHC) staining was performed to validate the tumor microenvironment.ResultsIrradiation markedly retarded tumor growth in the orthotopic HCC model and led to increaes in ADC values as early as on day 1 after irradiation. Irradiation also resulted in increases in F-18-FDG uptake on day 1 that were sustained until the end of the observation period. IHC staining revealed a decrease in the number of proliferative cells and a continuous macrophage influx into irradiated tumors, which dramatically altered the tumor microenvironment. Lastly, in vitro coculture of HCC cells and macrophages led to interaction between the cells and enhanced the cellular uptake of F-18-FDG.ConclusionADC values and F-18-FDG uptake measured using DW MRI and F-18-FDG PET serve as potential biomarkers for early assessment of HCC tumor responses to radiation therapy.