Purpose: The purpose of this study was to investigate the predictability of pretreatment values including Dynamic Contrast-Enhanced Magnetic Resonance Imaging (DCE-MRI) derived parameters (Ktrans, Kep and Ve), early changes in parameters (Ktrans, tumor volume), and heterogeneity (standard deviation of Ktrans) for radiation therapy responses via a human colorectal cancer xenograft model. Materials and Methods: A human colorectal cancer xenograft model with DLD-1 cancer cells was produced in the right hind limbs of five mice. Tumors were irradiated with 3 fractions of 3 Gy each for 3 weeks. Baseline and follow up DCE-MRI were performed. Quantitative parameters (Ktrans, Kep and Ve) were calculated based on the Tofts model. Early changes in Ktrans, standard deviation (SD) of Ktrans, and tumor volume were also calculated. Tumor responses were evaluated based on histology. With a cut-off value of 0.4 for necrotic factor, a comparison between good and poor responses was conducted. Results: The good response group (mice #1 and 2) exhibited higher pretreatment Ktrans than the poor response group (mice #3, 4, and 5). The good response group tended to show lower pretreatment Kep, higher pretreatment Ve, and larger baseline tumor volume than the poor response group. All the mice in the good response group demonstrated marked reductions in Ktrans and SD value after the first radiation. All tumors showed increased volume after the first radiation therapy. Conclusion: The good response after radiation therapy group in the DLD-1 colon cancer xenograft nude mouse model exhibited a higher pretreatment Ktrans and showed an early reduction in Ktrans, demonstrating a more homogenous distribution.
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