Example splitting

Authorship

Authors: J. A. Ramos-Mendez and B. A. Faddegon

Department of Radiation Oncology, University of California San Francisco

This example is provided by the Geant4-DNA collaboration.

These processes and models are further described at: http://geant4-dna.org

Any report or published results obtained using the Geant4-DNA software shall cite the following Geant4-DNA collaboration publications:

• Phys. Med. 31 (2015) 861-874
• Med. Phys. 37 (2010) 4692-4708

If use this example, please cite

• J Ramos-Mendez, et. Al. Phys. Med. Biol. 62(15), 5908-5925, (2017) DOI: 10.1088/1361-6560/aa7831

A brief description

The Splitting example uses variance reduction to improve the computational efficiency of calculations of ionization cluster size distributions. Ionization events are scored in a nanoscaled cylinder. Ionized electrons generated by the first generation of secondary electrons are split, i.e. new clone electrons are generated, labeled and propagated. The label is used to classify those new particles as if they were produced by independent histories to avoid overlapping of tracks at final analysis. The Splitting is performed only if the ionization event occurred in the cylinder.

Geant4-DNA processes are used.

The example package contains:

• source files (src, include)
• README
• .in, plot.C and visualization macro files

Set-up

The geometry is a nanoscaled cylinder centered in the world. The medium is water everywhere. The dimensions can be defined with

/detector/diameter  6 nm
/detector/length   10 nm

User can define the split number (default is 1, i.e. no split) with:

/vrt/numberOfSplit 10

How to run the example.

In interactive mode, run:

./Splitting
Idle> /control/execute vis.mac

In batch mode , run:

./Splitting run.mac

To get visualization, make sure to uncomment the #/control/execute vis.mac line in the macro.

Physics

This example shows:

• how to use the Geant4-DNA processes,
• how to implement the Splitting via G4WrappedProcess
• how to set the Splitting in specific region
• how to propagate new track information to secondary particles

A simple electron capture process is also provided in order to kill electrons below a chosen energy threshold, set in the Physics list.

Look at the PhyscisList.cc file.

Simulation output

The output results consists in two histograms in root format

• the energy deposit in the cylindrical target
• the frequency distribution of ionization cluster size

Important

Every time a value is added to a ROOT histogram, it contributes to the statistics. For this example, to correct estimate the uncertainties is recommended to split the simulation into several jobs and to calculate the statistics from them: batch mode. Otherwise, the statistical uncertainty may be underestimated.

Contact

If you have any questions or wish to notify of updates and/or modification please contact:

J. Ramos-Mendez at joser.nosp@m.m84@.nosp@m.gmail.nosp@m..com

Acknowledgments

Sebastien Incerti (CNRS) for its guidance