Quantitative Assessment of Tumor Responses after Radiation Therapy in a DLD-1 Colon Cancer Mouse Model Using Serial Dynamic Contrast-Enhanced Magnetic Resonance Imaging

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 (K-trans, K-ep and V-e), early changes in parameters (K-trans, tumor volume), and heterogeneity (standard deviation of K-trans) 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 (K-trans, K-ep and V-e) were calculated based on the Tofts model. Early changes in K-trans, standard deviation (SD) of K-trans, 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 K-trans than the poor response group (mice #3, 4, and 5). The good response group tended to show lower pretreatment K-ep, higher pretreatment V-e, and larger baseline tumor volume than the poor response group. All the mice in the good response group demonstrated marked reductions in K-trans 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 K-trans and showed an early reduction in K-trans, demonstrating a more homogenous distribution.