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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!