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

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 LNS PRESENT TREATMENT ROOM

Scattering system Modulator & Range shifter Monitor chambers Ligth field Laser

30 50 Patient Distribution Total number of patients : 84 Mean age: 57.6 yrs

Hadrontherapy GEANT4 Example First release: june 2004 – GEANT 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 test processP-valueTest Standard.0.069OK Standard + Had.0.40OK Low Energy0.51OK Low En. + Had0.699OK

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

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!