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.