Forrest Iandola and Joseph Perl
7/5/2011
Forest Iandola
1) Very nice
2) What are you comparing with? Data of what kind? Other simulations
(GEANT)?
3) Does GEANT do collimators?
4) What exactly is the comparison: (a-b)/a
Project 1 –Validation of Tool for Particle Simulation (TOPAS)
Tool for Particle Simulation (TOPAS) enables the simulation of proton beam cancer therapy scenarios. A collaboration of scientists from SLAC, Massachusetts
General Hospital, and UC San Francisco is currently developing TOPAS. Alpha testers at select institutions currently use TOPAS, Beta testing will begin Fall 2012, and TOPAS will launch for public use in Fall 2013.
Validation is a crucial step in the development of physics simulations such as
TOPAS. Some application developers validate their simulations by implementing realworld cancer treatments in their simulations. Then, these developers compare the simulation results with the real-world results. However, a host of subtle flaws in the simulation software may conspire to make the simulation results differ significantly from the real-world measurements. When the simulation of a complex cancer treatment scenario yields inaccurate results, it is inevitably difficult to determine the causes of the errors.
Instead of starting with complicated cancer treatment scenarios, our strategy for validating TOPAS begins with the implementation of simple benchmarks. Our benchmarks will include shooting particles at boxes, cylinders, and spherical volumes that are subdivided along various Cartesian, cylindrical and spherical axes. We will verify the correctness of TOPAS on these simple benchmarks by comparing output data from
TOPAS with hand calculations and real-world results.
Validating the correctness of TOPAS will serve as the fundamental result of this study. In addition, this study will yield a collection of well-documented benchmarks that may aid in the validation of future medical physics simulation tools.
Project 2 – Representing Proton Beam Apertures with Computational Geometry
In most proton therapy facilities, an extensive beamline lies between the proton source and the patient. This beamline typically includes components such as collimators, magnets, a range modulator, scatterers, and an aperture. The aperture sits close to the patient. The center of an aperture contains a hollow space. The outline of the hollow space matches the projection of the planning target (the tumor plus some additional treatment margin) into the plane of the treatment beam. Thus, the aperture collimates the protons into the shape of the tumor.
This study seeks to represent apertures with computational geometry. Our first step is review the methods currently used for representing apertures in other physics simulation software. We will also review computational geometry literature (not specific to medical physics simulations) for applicable strategies.
From our literature survey, we will extract a few geometrical methods that have a theoretical basis for being fast and accurate. We will implement each of these aperture representations in C++.

Forrest Iandola and Joseph Perl
7/5/2011
After implementing a number of aperture representation methods, we will benchmark the methods for both accuracy and performance. Our accuracy benchmarking will consist of testing the aperture representation methods in simulations of welldocumented cancer treatment case studies. We will compare the fluence received by the patient in each aperture representation method with existing data measured from apertures at the Francis H. Burr Proton Therapy Center.
In addition, we will conduct performance benchmarking to test the computation time of each of aperture implementation. Specifically, we will test the computation time needed for each method to check whether each of a collection of points is inside or outside the aperture’s volume.
Benchmarking will show which aperture representation method offers the best performance without compromising accuracy. The method that performs best in our benchmarks will be used for representing apertures in TOPAS.