A graticule for evaluation of megavolt X-ray port films

Simulator films and port films are important documents of quality assurance of treatment delivery. Graticules have been constructed for linear accelerators which project mutually perpendicular arrays of equi-spaced dots on X ray films, similar to those projected by a graticule on the simulator. The spacing corresponds to 2 cm at the isocentric distance. The projected dot arrays function as built-in rulers in the films and greatly facilitate quantitative comparison of simulator films and treatment verification films, regardless of film magnification