Monte Carlo Based Monte Carlo Based Implementation of an Energy Implementation of an Energy Modulation System for Proton Modulation System for Proton
TherapyTherapy
G.A.P. CirroneQualified Medical Physicist
PhD
Laboratori Nazionali del SudIstituto Nazionale Fisica
Nucleare
Catania, Sicily
What is the hadron-therapy?
Use of ions for the radiotherapeutic treatment of
tumours
LNS Superconducting Cyclotron is the unique machine in in Italy and South Europe
used for protontherapy
Treatment of the choroidal and iris
melanoma
In Italy about 300 new cases for year
• 0 ° respect the switching magnet
• 80 meter after extraction
• 3 m proton beam line
LAYOUT OF LNSPRESENT TREATMENT ROOM
Scattering system
Modulator & Range shifter
Monitor chambers
Ligth field
Laser
58%
42%
Women
Men
30 50
Patient Distribution
1
16
29
6
0
5
10
15
20
25
30
Nu
mb
er o
f p
atie
nts
0-25 25-50 50-75 75-100
Patients' age
20
6
5
5
5
4
2
2
1
1
1
Total number of patients :
84
Mean age: 57.6 yrs
Hadrontherapy GEANT4 Example
First release: june 2004 – GEANT4 6.2
1. A generic hadron therapy beam line can be reconstructed with all its elements;
2. Each element can be changed in shape, size, position, material via idle;
3. A final collimator or a modulator can be inserted;
4. The Bragg curve as well as a lateral dose distribution can be obtained at the end of each run (two detectors are simulated);
Beam Line Simulation
Collimator system
Scattering system
Monitor chamber system
Real hadron-therapy beam line
GEANT4 simulation
Detector simulated as a 3D cube (RO Geometry Class)
Energy collected in each voxel at the end of a run
(End of Run Action)The cube shape can be changed:
•A plane for the GAF simulation
•A small cylinder for the Markus simulation
•The whole cube if all the informations are needed
RO Geometry for 3D dose collection
Physics models: comparison with experimental data
Standard Processes
Standard + hadronic
Low Energy
Low Energy + hadronic
Kolmogorov testprocess P-value Test
Standard. 0.069 OK
Standard + Had. 0.40 OK
Low Energy 0.51 OK
Low En. + Had 0.699 OK
Isodose curves comparison
Lateral Distribution: comparison with experimental data
Beam Line Simulation: THE MODULATION
TUMOUR
MODULATOR WHEEL
Pure Bragg Peak
Spread Out Bragg Peak (SOBP)
Modulator consists of four identical sectors
It’s sufficient simulate only a wing
Only G4Tubs Class
The modulator needs to be rotated around its axis parallel to the proton
beam direction
Each modulator wing consists of superimposition of many G4Tubs elements each having different angular openings and starting
angles
Starting angle
Angular opening
G4Tubs class permits to define a cylinder defining its height,
material, a starting angle and an opening angle
Simulation example of the first slice
Common parameters for all slices
Particular parameters for this slice
The mother volume of the modulator is a simple air-box volume. It’s permits the rotation of modulator just changing
its angle
Modulator is included from a different file.icc to simplify the
DetectorConstruction file
The only parameter (ModulatorAngle) describing the rotation is imported via Messenger class method from an
user-defined input file, which contains the angle of the wheel as a function of the time
The modulator angle is modified calling the GeometryHasBeenModified
function
We delete and reconstruct only the part of geometry
which contains the modulator not updating
the entire geometry
Contribution from different modulator angles
The Spread Out Bragg Peak
The Spread Out Bragg Peak
Main dosimetric parameters (diff. Less than 5 %)
Conclusion & developments
1. A proton therapy transport beam line can be easily reconstructed;
2. Depth and lateral dose distribution agree with experimental data;
3. A modulated (theraputhical) proton beam can be reproduced with the GEANT4 toolkit;
FOLLOWING STEP
Comparison of our Monte Carlo application with the output of the
treatment planning system normally used in proton therapy
Thank you!