An X-ray irradiation apparatus includes an enclosure and an X-ray beam system positioned within the enclosure for directing X-ray beams into an irradiation region. The X-ray beam system has more than one X-ray beam emitter for directing the X-ray beams into the irradiation region from different directions. Each X-ray beam emitter includes a vacuum chamber having a target window and an electron generator positioned within the vacuum chamber for generating electrons that are directed at the target window for forming X-rays which pass through the target window as an X-ray beam. The target window is supported by a support plate having a series of holes therethrough which allow passage of the electrons therethrough to reach the target window.