# The TOPAS Tool for Particle Simulation, a Monte Carlo Simulation Tool for Physics, Biology and Clinical Research

> **NIH NIH U24** · UNIVERSITY OF CALIFORNIA, SAN FRANCISCO · 2021 · $848,679

## Abstract

The TOPAS TOol for PArticle Simulation, launched on NCI funding in 2009, is a breakthrough software project
that struck down a usability barrier that was limiting cancer research and treatment. Improvements to
radiotherapy and imaging require understanding how subatomic particles travel through apparatus and tissue.
The most precise calculations of such motion follow the Monte Carlo (MC) method. Yet MC's painstaking
specialized computer programming techniques had limited its availability to a small number of specialists.
TOPAS brings a reliable, experimentally validated and easy-to-use MC tool within reach of every physicist.
Requiring no programming knowledge, TOPAS provides nearly unlimited flexibility. It enables both clinical
applications (e.g. high precision patient dose calculation) and cutting edge research (e.g. four dimensional
time-of-flight simulations for detector developments), while its design promotes inter-institutional collaboration.
In 2013, on a second NCI award, TOPAS was expanded from its initial focus on proton therapy physics to also
cover radiation biology. TOPAS has been widely accepted in proton therapy physics and biology with 272
users at 121 institutions in 24 countries, but those working on other radiotherapy modalities and medical
imaging lack such a tool. We seek to address these needs, creating the only fully integrated platform for
advanced radiotherapy including multi-modality treatments and a broad range of image guidance. We shall:
Specific Aim 1: Enhance the TOPAS Environment for User-Friendly Interactive Modeling and Simulation
· Expand support for multi-processor, cluster, cloud and grid environments
· Improve I/O compatibility with other medical physics standards
· Improve computational speed and Graphical User Interface
Specific Aim 2: Extend TOPAS Capabilities for Translational and Clinical Applications
· Library of radiotherapy and imaging components, simplify simulation of complex therapy, QA and shielding
· Biological models for radiation protection and pre-clinical research
· Imaging systems and patient simulation, including more complex patient models
Specific Aim 3: Maintain TOPAS for all User Communities
· Respond to changes in underlying software packages and operating systems
· Expand automated regression testing system for quality control
Specific Aim 4: Disseminate TOPAS with Full Participation in ITCR Program Activities
· Disseminate TOPAS through workshops at key conferences and web site
· Provide user support through online user forum, web-based training and twice-yearly in-person trainings
· Develop TOPAS user collaboration, initiate projects to address key user needs identified post-award,
 maintain depository for users to exchange customizations and extensions, move TOPAS to open source

## Key facts

- **NIH application ID:** 10167645
- **Project number:** 5U24CA215123-04
- **Recipient organization:** UNIVERSITY OF CALIFORNIA, SAN FRANCISCO
- **Principal Investigator:** BRUCE FADDEGON
- **Activity code:** U24 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $848,679
- **Award type:** 5
- **Project period:** 2018-06-04 → 2023-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10167645

## Citation

> US National Institutes of Health, RePORTER application 10167645, The TOPAS Tool for Particle Simulation, a Monte Carlo Simulation Tool for Physics, Biology and Clinical Research (5U24CA215123-04). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10167645. Licensed CC0.

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