A method and apparatus for quality assurance of an image guided radiation treatment delivery system. A quality assurance ("QA") marker is positioned at a preset position under guidance of an imaging guidance system of a radiation treatment delivery system. A radiation beam is emitted from a radiation source of the radiation treatment delivery system at the QA marker. An exposure image of the QA marker due to the radiation beam is generated. The exposure image is then analyzed to determine whether the radiation treatment delivery system is aligned.