The microtrack example presents a geometry to calculate microdosimetry quantities for ion tracks in liquid water at a given energy, ensuring secondary electron equilibrium when needed. At each event, a random track hit defines a spherical scoring site; weighted sampling is then used to estimate energy imparted and related quantities.

Reference paper of this example:

Front. Phys. 9 (2021) 726787

This example is provided by the Geant4-DNA collaboration.

Geant4-DNA processes and models are documented at: http://geant4-dna.org

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

Med. Phys. 51 (2024) 5873–5889
Med. Phys. 45 (2018) e722-e739
Phys. Med. 31 (2015) 861-874
Med. Phys. 37 (2010) 4692-4708
Int. J. Model. Simul. Sci. Comput. 1 (2010) 157–178

2. Geometry

A box-shaped World of liquid water (G4_WATER) centered at the origin.
A box-shaped sensitive detector volume (SDbox) is created inside the world, centered at the origin. Its X/Y dimensions match those of the world.

The size of both volumes is determined by the parameters listed below:

Configurable geometry parameters:

/mygeom/material <name>: material of world/SD (default G4_WATER).
/mygeom/maxRange <value> [um|mm|cm]: maximum electron range.
/mygeom/hitSelRegZ <value> [um|mm|cm]: half-thickness of the central zone, within the SDbox, where energy transfer points (hits) are eligible for the random placement of the site.
/mygeom/hitSelRegXY <value> [um|mm|cm]: XY size of the central zone, within the SDbox, where energy transfer points (hits) are eligible for the random placement of the site.
/mygeom/siteRadius <value> [um|mm|cm]: radius of the site.

3. Particle source

Primary generator: G4ParticleGun with one particle per event. The source Z0 position is typically set at the world edge, pointing towards the SDbox. To achieve the desired energy at the SDbox center, the user may want to set the energy considering the expected energy loss from Z0 to the center.
Example: protons at 20.13 MeV from z_0 = -50.99 um, to achieve 20 MeV at z=0.

Configurable beam parameters (via UI):

/gun/particle <name>: e.g., proton, e-, ions available via G4DNAGenericIonsManager.
/gun/energy <value> [Energy]: kinetic energy compensated with (dE/dz)*Z0.
/beam/position/Z0 <value> [Length]: source position along Z coordinate.

The example macro run.mac sets proton at 20.13 MeV and Z0 = -50.99 um.

4. Physics

Default physics: G4EmDNAPhysics_option2.
Alternative lists can be selected at pre-init using:
- /physics/addPhysics dna_opt1|dna_opt2|dna_opt3|dna_opt4|dna_opt5| dna_opt6|dna_opt7|dna_opt8
- /physics/addPhysics liv (Livermore)
- /physics/addPhysics penelope
- /physics/addPhysics em_standard_opt4

Production cuts can be set:

/run/setCutForAGivenParticle gamma <L>
/run/setCutForAGivenParticle e- <L>
/run/setCutForAGivenParticle e+ <L>
/run/setCutForAGivenParticle proton <L>

5. Scoring

All energy depositions (Hits) are recorded in the sensitive detector. At end of each event:

One valid hit is randomly selected within the Hit Selection Region.
A spherical site (radius siteRadius) centered around a random offset within the sphere around this hit is defined. This procedure ensures that the spherical site sampled from a hit at the Hit Selection Region edge remains fully contained within SDbox.
For each event, we compute:
- Edep: total energy imparted inside the site.
- Nsel: number of hits in the Hit Selection Region.
- Nsite: number of hits in the site.
- Weighted and squared-weighted quantities are also histogrammed.
- KinE_in / KinE_out at the SD boundary for primary particles.

Output produced via Geant4 analysis (ROOT by default, multi-thread merge enabled):

File: microtrack.root in the run directory.
- Histograms:
  - H1[0]: f(E_{dep}) (single event energy imparted)
  - H1[1]: E_{dep} f(E_{dep}) (weighted single event energy imparted)
  - H1[2]: E_{dep}^2 f(E_{dep}) (squared-weighted single event energy imparted)
  - H1[3]: f(y) (lineal energy)
  - H1[4]: y f(y) (weighted lineal energy)
  - H1[5]: y^2 f(y) (squared-weighted lineal energy)
  - H1[6]: f(z) (specific energy)
  - H1[7]: z f(z) (weighted specific energy)
  - H1[8]: z^2 f(z) (squared-weighted specific energy)
  - H1[9]: N_{sel} (number of hits within the central selection region)
  - H1[10]: N_{site} (number of hits within the site)
  - H1[11]: N_{int} (number of hits within the site and the central selection region)
  - H1[12]: KinE_in (kinetic energy of primaries at SDbox upstream plane)
  - H1[13]: KinE_out (kinetic energy of primaries at SBbox downstream plane)
  - H2[0]: N_{site} vs E_{dep}.

6. Build and run

Prerequisites:

Geant4 built with analysis, UI and visualization if desired.

Configure and build (out-of-source recommended):

mkdir build && cd build
cmake ..
make -j

Run in batch mode with provided macro:

./microtrack run.mac

Interactive with visualization:

./microtrack

In the UI session, the visualization is configured by init_vis.mac and vis.mac.

Multi-threading: Set threads before initialization, e.g. in macro: /run/numberOfThreads 10.

7. Example macro (run.mac)

The provided run.mac configures a water world/SD, considering G4EmDNAPhysics_option2, proton beam at 20.13 MeV from z = -50.99 um, sites radius of 0.5 um, and 20 events. See the file for details and as a template.

8. Notes and limitations

Site selection uses a random hit within the Hit Selection Region; events with no eligible hits are skipped from analysis.

9. Acknowledgments and citations

This example is provided by the Geant4-DNA collaboration. Please cite the publications listed above.

README.md Unescape Escape

Geant4-DNA microtrack example

1. Introduction