Transcript Document
Monte Carlo Based Implementation
of an Energy Modulation System for
Proton Therapy
G.A.P. Cirrone
Qualified Medical Physicist
PhD
Laboratori Nazionali del Sud
Istituto Nazionale Fisica Nucleare
Catania, Sicily
What is the hadron-therapy?
Use of ions for the radiotherapeutic
treatment of tumours
120
8 MV X-rays
200 MeV protons
20 MeV electrons
cobalt 60
% dose response
100
80
60
40
20
0
0
5
10
15
20
depth cm of water
25
30
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
PRESENT
TREATMENT
ROOM
LAYOUT
OF LNS
• 0 ° respect the switching magnet
• 80 meter after extraction
• 3 m proton beam line
Ligth
field
Laser
Modulator &
Range shifter
Monitor
chambers
Scattering
system
Patient Distribution
5
1
Total number of
patients : 84
2
5
1
4
6
1
5
2
20
Mean age: 57.6 yrs
29
30
50
58%
30
Number of patients
42%
Women
Men
25
16
20
15
6
10
1
5
0
0-25
25-50
50-75
Patients' age
75-100
Hadrontherapy GEANT4 Example
First release: june 2004 – GEANT4 6.2
1. A generic hadron therapy beam
reconstructed with all its elements;
line
can
be
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
Scattering system
Collimator system
Monitor chamber system
Real hadron-therapy
beam line
GEANT4 simulation
RO Geometry for 3D dose collection
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
Physics models: comparison with experimental data
Standard +
hadronic
Standard
Processes
Kolmogorov test
process
P-value
Test
Standard.
0.069
OK
Standard + Had.
0.40
OK
Low Energy
Low Energy
Low En. + Had
0.51
0.699
Low Energy
OK
+ hadronic
OK
Lateral Distribution: comparison with experimental data
Isodose curves comparison
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
Starting angle
Angular opening
G4Tubs class permits to define a
cylinder defining its height,
material, a starting angle and an
opening angle
Each modulator wing consists of
superimposition of many G4Tubs
elements each having different
angular openings and starting
angles
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
We delete and reconstruct
only the part of geometry
which contains the
modulator not updating
the entire geometry
The modulator angle is modified calling
the GeometryHasBeenModified
function
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 Spread Out Bragg Peak
Contribution from
different modulator
angles
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!