| Description | I will discuss the motivation for use of Monte Carlo particle transport simulation in medical physics and radiation biology - why precision requirements in these fields are so significant, and how our understanding is moving beyond the concept of Dose to more complex quantities such as Relative Biological Effectiveness. I will then present the TOPAS - TOol for PArticle Simulation - a tool that makes such simulation more readily available for researchers in medical physics and radiation biology. TOPAS can model any form of radiation therapy or medical imaging apparatus, model a patient geometry based on CT (computed tomography) 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 or imaging. TOPAS users configure pre-built components (nozzle, patient handling, dosimetry or imaging components) to simulate a wide variety of particle therapies with no required knowledge of its underlying Geant4 Simulation Toolkit or any programming languages. 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. TOPAS is funded by the US National Cancer Institute and developed by the SLAC National Accelerator Laboratory, Massachusetts General Hospital and the University of California San Francisco. At last count TOPAS had 706 licensed users at 285 institutions in 37 countries. TOPAS is further described at www.topasmc.org |