To determine a treatment field for radiation therapy, a conventional X-ray simulator has been used so far. However, exact extension of the tumor can not be obtained by a conventional X-ray simulator, and, it is often difficult to simulate the treatment field obtained by CT on a conventional X-ray simulator. We have developed a method to produce a beam's eye projection through axial CT data, which has an identical geometrical location as verification film taken by the anticipated treatment beam called process Computed Simulationgraphy. The process and image enable treatment planning, making the treatment field on the patient's skin and verifying the port film.
