TOPAS is a user-friendly simulation software layered upon the general-purpose Geant4 particle transport toolkit. It was designed specifically for medical physics applications by MGH, Stanford and UCSF.

TOPAS software is available here and the documentation is here.

Key MGH personnel involved

  • Harald Paganetti, PhD (PI)
  • Jan Schuemann, PhD
  • Jungwook Shin, PhD
  • Aimee McNamara, PhD
  • David Hall, DPhil


  • Joseph Perl (SLAC)
  • Bruce Faddegon (UCSF)
  • Jose Ramos Mendez (UCSF)