FREDONE, A PROJECT ON DOSIMETRY OF HIGH ENERGY NEUTRONS Valérie De Smet (1), Isabelle Gerardy (2), Fréderic Stichelbaut (3), (1) IRISIB, Département nucléaire, Rue Royale 150, 1000 Bruxelles, Belgium (2) ISIB, Haute Ecole Spaak, Bruxelles, Belgium (3) Ion Beam Applications S.A. (IBA), Chemin du Cyclotron 3, 1348 Louvain-la-Neuve, Belgium.

T HE “ FREDONE ” PROJECT Research project funded by the Walloon region Includes a collaboration with an industry: Ion Beam Application s.a. (IBA) Evaluation (measurement) of the ambient dose equivalent for neutron energy up to 230 MeV. Present situation: study of the WENDI 2 extended range neutron detector and comparison between H*(10) measured and calculated using MCNPX code

A PROTON - THERAPY CENTER

T HE W ENDI -2 REM - METER Extended range to E n > 15 MeV due to Tungsten shell; spallation reactions Response of the detector: Calibration factor Evaluated with a Cf-252 source Neutron energy spectrum = fission spectrum

C OMPARISON BETWEEN M ONTE C ARLO SIMULATIONS AND H*(10) MEASUREMENTS PERFORMED WITH A WENDI-2 DETECTOR INSIDE A PROTON THERAPY FACILITY Actual situation of the research Poster presented during the NEUDOS symposium (Aix-en-Provence, 3 – 7 June 2013) Collaboration: IRISIB and ISIB IBA s.a. ULB, Inter-university Institute for High Energies (IIHE), ULB, Service de Métrologie Nucléaire

I NTRODUCTION AND GOAL Scope : accurate measurement of the H*(10) for high energy neutrons (up to 230 MeV) produced in a proton therapy facility by interaction of proton with matter in the cyclotron in the beam line in the nozzle in the patient Measurements with the WENDI 2 H*(10) depends on the neutron energy spectrum Comparison with Monte Carlo H*(10) calculation obtained in different neutron spectra (different positions) WENDI-2 detector Treatment nozzle

E VALUATION IN THE CYCLOTRON ROOM Model of the cyclotron hall H*(10) calculated by MCNPX GEANT4 9.6 (by T. Vanaudenhove) Measurement with WENDI-2 a bc de f g average current extracted from cyclotron: 150 nA

E VALUATION IN THE GANTRY ROOM h i jk l m no p q Beam Water phantom Gantry stop block Gantry counter- weight Gantry isocenter Gaussian proton beam σ = 3 mm Water phantom Gaussian proton beam σ = 3 mm Water phantom Gantry isocenter First scatterer Second scatterer Range modulator Pencil beam scanning Double scattering

P ENCIL BEAM SCANNING Active technique, a narrow beam “scans” the tumour Ratio between 1.85 and 4.08 out of the gantry room ~17 in Position “o” Proton dose rate: ~2 Gy/min

D OUBLE SCATTERING Passive technique, scattering materials used to enlarge the beam Ratio between 2.17 and 7.30 for all measured points Highest value in Position “o” Proton dose rate: ~2 Gy/min

C ONCLUSIONS OF THIS STUDY Good agreement obtained between the MCNPX and GEANT4 results of the neutron ambient dose equivalent H*(10). The results differ by at most a factor 2 between the two codes. For most of the considered positions, MCNPX is the code that yields the largest values. In all considered positions located outside the shielded rooms, the simulation results obtained with both codes overestimate the measured data obtained with the WENDI-2. Factor between 1.85 and 7.30, except for one position in the PBS study (factor of 16.6, MCNPX). In future work, the systematic uncertainties associated to the simulation results will be investigated through sensitivity analyses concerning geometrical aspects, material definitions and physics models.

E XTENSION OF COLLABORATION : Academic : University of Bologna by means of the subject of a master thesis in 2012 Université Libre de Bruxelles (ULB) became an scientific partner in 2011 ; the researcher was admitted in the doctoral school of the Inter-university Institute for High Energies With research center: CRC (Belgium LLN): measurements in quasi-monoenergetic neutron beams of 33 and 60 MeV a calibrated continuous neutron spectrum  foreseen in the next three months Possibility of performing measurements in monoenergetic neutron beams up to 246 MeV in RCNP (Osaka, Japan) in collaboration with the dosimetry unit of the CERN; foreseen in October 2013

F UTURE DEVELOPMENTS Study of SP2 detector Allowing an evaluation of the neutron spectrum Polyethylene sphere containing Dy foils at different depth  reconstruction of the spectrum but not sensitive enough for low dose rate situation Evaluation of the response of TEPC detector Direct evaluation of the H*(10) using micro- dosimetry techniques Evaluation of the Q factor of the secondary particles produced in tissue Possible master or PhD thesis