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!