A personal‐computer‐based method to obtain “star‐shots” of mechanical and optical isocenters for gantry rotation of linear accelerators

This work describes a method to obtain “star‐shots” of the mechanical and optical isocenters of linear accelerators, similar to the star‐shots of radiation isocenters normally obtained using films. In this method a digital camera is connected to a personal computer so that multiply exposed images can be taken at a fixed camera position. A mechanical pointer or a wire aligned along the optical axis can then be imaged by the camera. Multiple exposures at varying gantry angles are then superimposed on a digital image which can be analyzed by the computer to give a high‐resolution star‐shot. The method provides a convenient way for a linear accelerator quality assurance procedure.