Monte Carlo Based Implementation of an Energy Modulation System for Proton Therapy

1. Monte Carlo Based Implementation of an Energy Modulation System for Proton Therapy G.A.P. CirroneQualified Medical PhysicistPhD Laboratori Nazionali del SudIstituto Nazionale Fisica Nucleare Catania, Sicily

2. What is the hadron-therapy? Use of ions for the radiotherapeutic treatment of tumours

3. 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

4. PRESENT TREATMENT ROOM • 0 ° respect the switching magnet • 80 meter after extraction • 3 m proton beam line LAYOUT OF LNS

5. Modulator & Range shifter Ligth field Scattering system Monitor chambers Laser

6. Patient Distribution 5 1 2 5 1 4 6 1 5 2 20 30 50 Total number of patients : 84 Mean age: 57.6 yrs

7. Hadrontherapy GEANT4 Example First release: june 2004 – GEANT4 6.2 • A generic hadron therapy beam line can be reconstructed with all its elements; • Each element can be changed in shape, size, position, material via idle; • A final collimator or a modulator can be inserted; • The Bragg curve as well as a lateral dose distribution can be obtained at the end of each run (two detectors are simulated);

8. Beam Line Simulation Scattering system Collimator system Monitor chamber system

9. GEANT4 simulation Real hadron-therapy beam line

10. 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

11. Physics models: comparison with experimental data Standard + hadronic Standard Processes Low Energy + hadronic Low Energy

12. Lateral Distribution: comparison with experimental data Isodose curves comparison

13. TUMOUR Beam Line Simulation: THE MODULATION

14. 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

15. 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

16. Simulation example of the first slice Common parameters for all slices Particular parameters for this slice

17. 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

18. 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

19. The Spread Out Bragg Peak Contribution from different modulator angles

20. Main dosimetric parameters (diff. Less than 5 %) The Spread Out Bragg Peak

21. Conclusion & developments • A proton therapy transport beam line can be easily reconstructed; • Depth and lateral dose distribution agree with experimental data; • 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

22. Thank you!