Welcome to TOPAS MC Inc., a non-profit organization to support and extend the TOPAS Tool for Particle Simulation.


12 August 2021: TOPAS Version 3.7 is Released. Licensed users can see details in the User Forum and the Code Repository.

TOPAS wraps and extends the Geant4 Simulation Toolkit to make advanced Monte Carlo simulation of all forms of radiotherapy easier to use for medical physicists. TOPAS can model x-ray and particle therapy treatment heads, model a patient geometry based on CT images, score dose, fluence, etc., save and replay a phase space, provides advanced graphics, and is fully four-dimensional (4D) to handle variations in beam delivery and patient geometry during treatment. TOPAS users configure pre-built components (such as nozzles, patient geometry, dosimetry and imaging components) to simulate a wide variety of radiation therapies with no required knowledge of the underlying Geant4 Simulation Toolkit or any programming language. All aspects of the simulation, including all 4D behaviors, are controlled from a unique, TOPAS Parameter Control System. TOPAS was engineered from the ground up to be flexible, yet easy to use, reliable and repeatable. The code includes a strong focus on “engineering-in” safety, employing a variety of techniques to make it harder for users to make mistakes. Two very brief introduction to TOPAS videos can be found here and here.

TOPAS is further described in the open-access manuscript: Perl J, Shin J, Schumann J, Faddegon B, Paganetti H. TOPAS: an innovative proton Monte Carlo platform for research and clinical applications. Med Phys. 2012 Nov; 39(11):6818-37. (View in: PubMed).This manuscript has has been cited 578 times in Google Scholar.

TOPAS basic concepts were originally created out of an NIH-funded collaboration of the SLAC National Accelerator Laboratory, Massachusetts General Hospital and the University of California at San Francisco. Following Beta testing by a community of users at 88 institutions, Stanford University has granted TOPAS MC Inc. the license to the copyrighted kernel of TOPAS so that we can distribute TOPAS to end-users and collect license fees that fund further development and user support. At last count we had 1828 licensed users at 515 institutions in 52 countries.

While most early applications of TOPAS have been in proton therapy, TOPAS is now available for use in all areas of radiation therapy research and is also suitable for some medical imaging applications. Work is ongoing to extend TOPAS to radiation biology and to science education. Other potential applications include studies of radiation damage to electronics, particle physics, nuclear physics and astrophysics.

Our mission is to make TOPAS into a tool that fits comfortably into the hands of every medical physicist.

Per user license cost ranges from Free to $2500. depending on class of user. See details under Types of Licenses.

TOPAS MC Inc. is a nonprofit public benefit corporation and is recognized by the IRS as a tax exempt public charity under section 501(c)(3).