Introduction to TOPAS

TOPAS wraps and extends the Geant4 Simulation Toolkit to provide an easier-to-use application for the medical physicist. TOPAS’s unique parameter control system lets you assemble and control a rich library of simulation objects (geometry components, particle sources, scorers, etc.) with no need to write C++ code.

Advanced users remain free to implement their own simulation objects in C++ code, and add them to TOPAS via an extension mechanism. While user-written objects benefit from underlying functionality of TOPAS base classes and the TOPAS parameter system, they can exploit the full flexibility of Geant4.

To discover the Geant4 version used by a specific version of TOPAS, please consult the History.


Users should carefully read the Introduction to Parameter System, as well as the introductory parts of the sections Geometry Components, Particle Sources, Physics and Scoring. The rest of the documentation provides a detailed reference that you may just want to skim initially.