The application of the Inverse Monte Carlo Ray Tracing (IMCRT) method to define the concentrator geometry of solar collectors with round absorbers is presented. Such absorber geometry is the most common in current commercial systems. Parabolic trough collectors (PTC) concentrate radiation onto the absorber tube generating a non-homogeneous flux distribution, which may cause thermal stress problems; especially the case in direct steam generation systems. The proposed methodology is applied to calculate new reflector geometries considering two different objective flux profiles. The results have been obtained regarding the solar sunshape and the glass cover refraction. The geometries obtained have been validated with a 2D in-house ray tracing code. (C) 2016 Elsevier Ltd. All rights reserved.