The reconstruction toolkit (RTK), an open-source cone-beam CT reconstruction toolkit based on the insight toolkit (ITK). The Reconstruction Toolkit (RTK) is an open-source and cross-platform software for fast circular cone-beam CT reconstruction based on the Insight Toolkit (ITK). RTK is developped by the RTK consortium. RTK provides or will provide: Basic operators for reconstruction, e.g., filtering, forward, projection and backprojection; Multithreaded CPU and GPU versions; Tools for respiratory motion correction; I/O for several scanners; Preprocessing of raw data for scatter correction.