8 May 2024: Funding update
In light of community response and support,  we can now assure users that the web site, code repository, documentation site and user forum will remain in place. Funding is still being sought to reach our larger goals of providing ongoing world-class support.

May 6, 2024: A message regarding other codes that have put TOPAS into their name can be found here.

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 over 1200 times in Google Scholar  – proof that TOPAS enables extensive and varied cancer solutions.

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. TOPAS MC Inc. serves as a central resource for TOPAS users. At last count, our TOPAS User and Development Community included 2956 users at 708 institutions in 71 countries.

TOPAS is applied in all areas of radiation therapy research and is also actively used in medical imaging research, radiation biology, materials science, particle physics and education. Other potential applications include studies of radiation damage to electronics, nuclear physics and astrophysics.

Our mission is to make TOPAS into a tool that fits comfortably into the hands of every scientist and engineer.

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).

This website, including all pages, is protected intellectual property, © 2014-2025 TOPAS MC Inc.