Technical note: Extension of Van Herk's treatment margin model for anisotropic systematic positioning errors in cartesian coordinate systema.

摘要

PURPOSE: A coefficient of a treatment margin model for anisotropic systematic positioning errors has been calculated in Cartesian coordinate system based on van Herk's analytical formulation. METHODS: Three-dimensional (3D) patient population distribution was formulated in Cartesian coordinate system to model anisotropic systematic positioning errors. Analytical 3D integration with anisotropic standard deviations Sigma's and the following Newton's method yielded the coefficient of van Herk's systematic positioning error model in Cartesian coordinate system. RESULTS: The treatment margins for the anisotropic systematic errors in Cartesian coordinate system were 2.1 Sigma for 90% patient population coverage and 2.4 Sigma for 95% patient population coverage. CONCLUSIONS: It was found that the treatment margins for anisotropic systematic positioning errors in Cartesian coordinate system were smaller than those for the isotropic model in spherical coordinate system for a given patient population coverage probability.