To develop a new MV x-ray detector with a high quantum efficiency and an adequate spatial resolution for image-guided radiotherapy, scintillating fibers with a diameter of 1 mm were embedded in lead to form a honeycomb pattern with a thickness of 2 cm. The properties of the detector were measured using a 6 MV beam on a Linac machine. The prototype detector has a quantum efficient of 35%, about an order of magnitude higher than that of current detectors used in the clinic. The spatial resolution of the prototype is comparable to that of video-based electronic portal imaging systems. The prototype detector can also suppress scattered signals which will help to improve the signal to noise ratio of the image. This work indicates that using scintillating fibers to generate and guide imaging signals, it is possible to increase the quantum efficiency and maintain an adequate spatial resolution for MV x-ray imaging.