Quantitative Correlation at the Molecular Level of Tumor Response to Docetaxel by Multimodal Diffusion-Weighted Magnetic Resonance Imaging and [18F]FDG/[18F]FLT Positron Emission Tomography

We aimed to quantitatively characterize the treatment effects of docetaxel in the HCT116 xenograft mouse model, applying diffusion-weighted magnetic resonance imaging (MRI) and positron emission tomography (PET) using 2-deoxy-2-[F-18] fluoro-D-glucose ([F-18] FDG) and 3'-deoxy-3'-[F-18]-fluorothymidine ([F-18] FLT). Mice were imaged at four time points over 8 days. Docetaxel (15 mg/kg) was administered after a baseline scan. Voxel-wise scatterplots of PET and apparent diffusion coefficient (ADC) data of tumor volumes were evaluated with a threshold cluster analysis and compared to histology (GLUT1, GLUT3, Ki67, activated caspase 3a). Compared to the extensive tumor growth observed in the vehicle-treated group (from 0.32 +/- 0.21 cm(3) to 0.69 +/- 0.40 cm(3)), the administration of docetaxel led to tumor growth stasis (from 0.32 +/- 0.20 cm(3) to 0.45 +/- 0.23 cm(3)). The [F-18] FDG/ADC cluster analysis and the evaluation of peak histogram values revealed a significant treatment effect matching histology as opposed to [F-18] FLT/ADC. [F-18] FLT uptake and the Ki67 index were not in good agreement. Our voxel-based cluster analysis uncovered treatment effects not seen in the separate inspection of PET and MRI data and may be used as an independent analysis tool. [F-18] FLT/ADC cluster analysis could still point out the treatment effect; however, [F-18] FDG/ADC reflected the histology findings in higher agreement.