G. Cosmo, S. Guatelli, M.G Pia

1
http//cern.ch/geant4/geant4.htmlhttp//www.ge.in
fn.it/geant4/events/salamanca.html
Brachytherapy exercise

• G. Cosmo, S. Guatelli, M.G Pia
• Salamanca, 15-19 July 2002

2
Plan of this exercise

• Learn the basics of how to build a simple user
  application
• Mandatory user classes
• Optional user actions
• Learn the basics of how to use interactive
  facilities
• User Interface
• Visualisation
• Histogramming
• How well proceed
• Illustrate design and implementation basic
  features
• Propose a simple exercise on the same topic
• Show the solution

3
Basics of user classes

• See lecture on Monday
• Would you like to refresh an overview of Geant4
  user classes?

4
User requirements (main ones listed only)
The application provides the simulation of dose
distribution of brachytherapic sources in a
phantom

• The user shall be able to change the absorber
  material of the phantom
• The user shall be able to change interactively
  the brachytherapic source
• The user shall be able to put sources in
  different positions inside the phantom
• Low Energy electromagnetic processes should be
  available
• The user shall be able to calculate the total
  absorbed energy in the phantom
• 3D distribution in the volume
• 2D distribution in the plane containing the
  source
• The dose should be collected 1mm voxels
• The user shall be able to define the isodose
  curves in the phantom
• The user shall be able to visualize the geometry
  involved and the trajectories of the particles

5
Part 1

• Use case model a brachytherapy seed and a
  phantom
• Use case model a 192Ir brachytherapy seed
• Use case model a water phantom
• Use case visualise the geometry
• Exercise model a soft tissue phantom
• Exercise select phantom material from the UI
• Exercise model a 125I brachytherapy seed
• Use case model the radioactive source as a
  primary generator of monocromatic photons
• Exercise model the spectrum of a 125I source

6
OOAD
7
Implementation

• Exercise Brachy1
• header files in include/.hh, source code in src/
  .cc
• main in Brachy.cc
• macro initInter.mac
• Classes
• BrachyDetectorConstruction
• BrachyPrimaryGeneratorAction
• BrachyPhysicsList
• BrachyRunAction
• BrachyEventAction
• - BrachyVisManager

8
How to run

• Define necessary environment variables
• source setup_brachy.csh
• How to compile and link
• gmake
• How to run
• G4WORKDIR/bin/Linux/Brachy

Default macro initInter.mac
9
(No Transcript)
10
Run Brachy1
At the idlegt prompt, type help, information
about interactive commands

• It will appear the visualization of the box
• It will appear idlegt (interactive mode)
• type /run/beamOn number of events
• The simulation is executed
• Type exit

OGLIX Immediate visualization
No images saved!
About Visualization
DAWN Interactive panel
images saved
Default visualization driver OGLIX Defined in
InitInter.mac
11
Model a 192Ir brachytherapy seed

• Open BrachyDetectorConstruction in the editor
• Follow the guided tour by Susanna
• How the geometry is build

ExpHall world volume
Phantom Box
Capsule of the source
the mother volume is the containing volume!
Iridium core
12
(No Transcript)
13
More about visualization
How to change driver in initInter.mac
/vis/open OGLIX /vis/open DAWNFILE
/vis/open OGLIX /vis/open DAWNFILE
How to work with DAWN

• How to work with OGLIX
• At the idlegt prompt
• Type help
• Type the number corresponding to /vis/
• Information about visualization commands
• Eg. rotation of the geometry
• magnification

• The interactive panel appears
• devices choose the format
• of the image
• camera choose the geometry
• parameters
• (rotation, magnification...)

14
Before starting
Documentation http//geant4.web.cern.ch/geant4
click on documentation
click on Users Guide
For Application Developers very useful
!
15
Exercise model a soft tissue phantom
element Fractional mass
H 0.104472
C 0.23219
N 0.02488
O 0.630238
Na 0.00113
Mg 0.00013
P 0.00133
S 0.00199
Cl 0.00134
K 0.00199
Ca 0.00023
Fe 0.00005
Zn 0.00003

• Composition of soft tissue material
• (from NIST data base)
• Guidance
• define necessary elements
• define tissue material
• associate the tissue material to the phantom
• volume
• SolutionBrachy2

16
Exercise select phantom material from UI

• Select a water/tissue phantom
• The user shall be able to change interactively
  the material of the phantom
• Guidance
• create a BrachyDetectorMessenger
• Create a BrachyDetectorMessenger pointer in
  BrachyDetectorConstruction
• Create the member function SetMaterial in
  BrachyDetectorConstruction
• Help! Novice example N02
• Solution Brachy3

17
ExerciseModel a simplified I-125 brachytherapic
sourcegeometry and materials

• 3 tubs
• Iodium core
• Air
• Titanium capsule tip (box)
• Titanium tube

Iodium core
Iodium core Inner radius 0 Outer radius
0.30mm Half length1.75mm
Titanium tube Outer radius0.40mm Half
length1.84mm
Mean gamma energy 28.45keV
Air Outer radius0.35mm half length1.84mm
Titanium capsule tip Box Side 0.80mm
Change the geometry of the source
in BrachyDetector Construction
18
Exercise model a 125I brachytherapy seed

• Guidance
• define necessary elements, materials
• define solids, logical volumes, physical volumes
• suggestion proceed incrementally (i.e. implement
  one/few features at a time, compile, verify that
  it is OK, add a new feature etc)
• Solution Brachy4
• In Brachy4 the initial energy of primary
  particles is 28.45 KeV

Pay attention to overlapping volumes the
simulation seems to run but after few events
it stops to work, it seems dead !
19
Model a monocromatic photon source

• Open BrachyPrimaryGeneratorAction in the editor
• Follow the guided tour by Susanna

20
Exercise model a source spectrum
Energy(keV) Probability
27.4 0.783913
31.4 0.170416
35.5 0.045671

• Description of the spectrum
• Guidance
• Change in the BrachyPrimaryGeneratorAction
• Introduce an array (my array) with 3
  cells(corr.3probabilities) in the constructor
• In the GeneratePrimaries method
• Solution Brachy5

To be implemented !
G4UniformRand() returns a number between 0 and 1
G4double randomG4UniformRand() G4double
sum0 G4int i0 while(sumltrandom) sum
myarrayi i ..
Generation of Random numbers
21
What you learned today

• The design of a basic user application
• The mandatory user classes
• The optional user classes
• How to describe materials
• How to model a simple geometry
• How to implement a DetectorConstruction
• How to visualise geometry and tracks
• How to control features from the user interface
• How to model the primary generator
• How to implement a UserPrimaryGeneratorAction

22
Part 2

• Use case calculate the energy deposit in a
  phantom from a brachytherapy seed
• Use case generate physics interactions in the
  phantom
• Exercise select alternative physics processes
• Exercise modify the production thresholds
• Use case collect the energy deposit in the
  phantom
• Exercise model the hits as consisting of the
  energy deposited in each voxel and the
  coordinates of the voxel centre
• Use case produce a 1-D histogram with the energy
  deposited in the phantom
• Exercise produce a 2-D histogram with the dose
  distribution in the phantom

23
(No Transcript)
24
Generate physics interactions

• Open BrachyPhysicsList in the editor
• Follow the guided tour by Susanna

25
Exercise select alternative processes

• Replace LowEnergy processes with standard ones
• For gamma and e-
• Change the production thresholds to 0.1mm for
  all the particles involved
• Guidance
• User Guide for Application Developers
• Physics ReferenceManual
• standard processes in geant4/source/processes/elec
  tromagnetic/standard/
• Solution Brachy6

26
Collect energy deposited in the phantom
Example Brachy7
This is the Geant4/examples/advanced/brachytherapy

• Open BrachyROGeometry, BrachyHit in the editor
• Follow the guided tour by Susanna

27
(No Transcript)
28
Exercise hits consisting of Edep, x,y,z

• Add Edep
• Associate Edep to the voxel coordinates
• Guidance
• In BrachyEventAction
• Take inspiration from
• Solution Brachy8

i((CHC)h)-gtGetZID() k((CHC)h)-gtGetXI
D()
29
Produce a 1-D histogram

• Open BrachyAnalysis, Brachy in the editor
• Follow the guided tour by Susanna

30
(No Transcript)
31
(No Transcript)
32
Exercise add a 2-D histogram

• Produce a 2-D histogram with the dose
  distribution in the phantom
• Guidance
• x, z, Edep in BrachyEventAction
• Edep is the weight
• Introduce 2-D histogram in BrachyAnalysisManager
• Similar implementation as in 1-D histogram
• Solution Brachy9

33
What you learned today

• How to select particles, physics processes and
  production thresholds
• How to implement a PhysicsList
• How to model the detector response
• read-out geometry, hits
• How to produce histograms in your simulation
  applications