Dr. Sandro Sandri ( President of Italian Association of Radiation Protection , AIRP)

1. THE RADIATION FIELDS AROUND A PROTON THERAPY FACILITY: A COMPARISON OF MONTE CARLO SIMULATIONS Dr. Sandro Sandri (President of ItalianAssociation of RadiationProtection, AIRP) Head, RadiationProtectionLaboratory, IRP FUAC Frascati ENEA – RadiationProtectionIstitute sandro.sandri@enea.it 12th International Symposium on Radiation Physics 07 to 12 October 2012 - Rio de Janeiro - RJ

2. CONTENTS S. Sandri - 12th International Symposium on Radiation Physics - Rio de Janeiro - RJ • The TOP-IMPLART • Scope of the analysis • Simulation model • The computer codes • Results • Discussion and conclusion

3. TOP-IMPLART accelerator • TOP-IMPLART are the acronym of TerapiaOncologica con Protoni (Oncological Therapy with Protons) and Intensity Modulated Proton Linear Accelerator for Therapy • The first 7 MeV module of the accelerator, is already installed and has been tested • Additional modules will be added leading proton energy to 30, 70 and 150 MeV • In the final layout the bunker will be 30 m long and 3 m wide S. Sandri - 12th International Symposium on Radiation Physics - Rio de Janeiro - RJ

4. COMPUTER CODES • The principal subject of the current work is the analysis of the performance of two different computer codes • both based on the Monte Carlo algorithm: • FLUKA (FLUktuierendeKAskade) and • MCNPX (Monte Carlo N-Particle eXtended) • Info on the web sites: • www.fluka.org • mcnpx.lanl.gov S. Sandri - 12th International Symposium on Radiation Physics - Rio de Janeiro - RJ

5. SIMULATION MODEL • The model has been developed to simulate a 150 MeV proton beam • hitting a water phantom of cubic form, 32 cm thick (32x32x32 cm3) • with 2 mm plexiglasswalls • and located in front to the kapton membrane, 50 µm thick, that seals the vacuum chamber of the accelerator • Between the kapton membrane and the phantom there is a 2 cm air gap • The cross section of the proton beam reaching the kapton membrane has the maximum dimension of 7 mm (in x and y directions) S. Sandri - 12th International Symposium on Radiation Physics - Rio de Janeiro - RJ

6. SECONDARY PARTICLES Several secondaries are generated in the inelastic interactions of the beam protons with the target components (plexiglass and water). Both the codes were able to follow the different produced particles and provided different kind of related results. FLUKA for examples provided the following table per beam particle S. Sandri - 12th International Symposium on Radiation Physics - Rio de Janeiro - RJ

7. NEUTRON PRODUCTION The comparison of the data for neutron production shows a reasonable agreement between the two codes. However using the libraries in MCNPX the neutron yield is about 7% higher 2,6% S. Sandri - 12th International Symposium on Radiation Physics - Rio de Janeiro - RJ

8. PARAMETERS OF COMPARISON • the comparison of the code concentrated on the following fluence results: • Proton fluence in the target and in air around the target • Neutron fluence in the target and in air around the target • Photon fluence in the target and in air around the target S. Sandri - 12th International Symposium on Radiation Physics - Rio de Janeiro - RJ

9. FLUKA protonfluence Water phantom • In FLUKA the spatial distribution of a quantity can be reported in a 2d chromatic picture • MCNPX doesn’t have this capability S. Sandri - 12th International Symposium on Radiation Physics - Rio de Janeiro - RJ

10. MCNPX protonfluence • MCNPX, Proton fluence in air, 100 cm after the target • The total proton flux of about 1 10-8 (8,44% uncertainty) is the same of FLUKA S. Sandri - 12th International Symposium on Radiation Physics - Rio de Janeiro - RJ

11. Photonfluence FLUKA MCNPX Discrepancies in the results for photons are mainly due to differentunits and scaling S. Sandri - 12th International Symposium on Radiation Physics - Rio de Janeiro - RJ

12. Neutronfluence FLUKA MCNPX Due to the differentunits, the qualitative pathonly can be compared in the graphs, showing a goodagreement S. Sandri - 12th International Symposium on Radiation Physics - Rio de Janeiro - RJ

13. FLUKA, Neutron fluence, spatial distribution Neutrons are more intense in the forwarddirection, asforeseeable S. Sandri - 12th International Symposium on Radiation Physics - Rio de Janeiro - RJ

14. CONCLUSIONS • Both computer codes used in the simulation are well suitable to be applied to the analysis of the secondary radiation produced by the proton beam of the TOP-IMPLART accelerator • While MCNPX seems to be more flexible in the data library selection and update, FLUKA can provide a more complete output in term of graphical detail • Another advantage of MCNPX is the availability of versions developed to run on the world wide diffused Windows™ personal computer, on the other hand FLUKA can be installed on a pc with Linux system • The results obtained with the two codes showed a good agreement for the fluencevs energy spectra of the neutrons (the main secondary radiation) • In conclusion both the codes are appropriate for the specific calculation and the selection should be mainly based on the hardware and operative system availability, and on the specific skilfulness of the users S. Sandri - 12th International Symposium on Radiation Physics - Rio de Janeiro - RJ