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Colloidal semiconductor nanocrystals exhibit physical properties that are characteristic of intermediate size scales between molecular states and solid state materials, and are often called quantum dots. Solid state semiconductor materials have been used extensively as scintillation detectors for ionizing radiation. We describe the use of semiconductor quantum dot - organic polymer composites for use as scintillation detectors and report the first use of quantum dot - polymer composite thin films for X-ray imaging. We have prepared quantum dot - polymer thin film samples using both aqueous CdTe quantum dots in polyvinyl alcohol and non-aqueous CdSe quantum dots in polystyrene. Optical absorption spectra and emission spectra are used to characterize the quantum dot morphology in the polymer film and to evaluate the impact of the host polymer matrix on the quantum dot dopant. We report the fluorescence lifetime changes of the quantum dots in the polymer host and discuss the impact on high frame rate X-ray imaging. The emission spectrum of the X-ray induced luminescence is found to have the same spectral dependence as the laser induced fluorescence. The details of the quantum dot - polymer composite scintillator fabrication and characterization will be discussed. The thin film substrates are coupled to a CCD camera and used to record X-ray images.