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.

THE “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 2.5.0 code

A PROTON-THERAPY CENTER

THE WENDI-2 REM-METER

Extended range to En > 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

COMPARISON BETWEEN MONTE CARLO 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

INTRODUCTION 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

EVALUATION IN THE CYCLOTRON ROOM

Model of the cyclotron hall H*(10) calculated by

MCNPX 2.5.0 GEANT4 9.6 (by T. Vanaudenhove)

Measurement with WENDI-2

•

ab c

def

g

average current extracted from cyclotron: 150 nA

max

*(10)6.35MCNPX

W

H

H

EVALUATION IN THE GANTRY ROOM

h

ijk

l

m

no

p

q

BeamWater 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

PENCIL 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

*(10)MCNPX

W

H

H

DOUBLE 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

*(10)MCNPX

W

H

H

CONCLUSIONS OF THIS STUDY

Good agreement obtained between the MCNPX 2.5.0 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 2.5.0 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.

EXTENSION 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

FUTURE 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