Fiber-coupled organic plastic scintillators present an attractive method for time-resolved dose measurements during radiotherapy. Most organic scintillators exhibit a fast response, making it possible to use them to measure individual high-energy X-ray pulses from a medical linear accelerator. This can be used in complex treatment procedures such as gated intensity-modulated radiotherapy (IMRT)1, where the advantage of dose rate measurements of high temporal resolution is highly emphasized. We report on development of a fast data acquisition scintillator-based system as well as measurements performed on Varian medical linear accelerators, delivering 6 MV X-ray beams. The dose delivery per radiation pulse was found to agree with expectations within roughly 1%, although minor discrepancies and transients were evident in the measurements.