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Tissue-Equivalent Phantom Materials for Neutron Dosimetry in Proton Therapy

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R Hälg

R Halg1*, S Clarke2 , B Wieger2 , E Pryser2 , R Arghal2 , S Pozzi2 , V Bashkirov3 , U Schneider4 , R Schulte3 , A Lomax1 , (1) Paul Scherrer Institut, Villigen-PSI, (2) University of Michigan, Ann Arbor, MI, (3) Loma Linda University Medical Center, Loma Linda, CA, (4) Radiotherapy Hirslanden, Zurich


SU-E-T-329 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To characterize tissue equivalence of phantom materials in terms of secondary neutron production and dose deposition from neutrons produced in radiation therapy phantom materials in the context of proton therapy using Monte Carlo simulations and measurements.

Methods: In order to study the influence of material choice on neutron production in therapeutic proton beams, Monte Carlo simulations using the Geant4 and MCNPX-PoliMi transport codes were performed to generate the neutron fields produced by protons of 155 and 200 MeV. A simple irradiation geometry was used to investigate the effect of different materials. The proton beams were stopped in slab phantoms to study the production of secondary neutrons. The investigated materials were water, Lucite, and tissue-equivalent phantom materials (CIRS Inc., Norfolk, VA). Neutron energy spectra and absorbed dose by neutrons and their secondary particles were scored. In addition, simulations were performed for reference tissues (ICRP/ICRU) to assess tissue equivalence with respect to neutron generation and transport. In order to benchmark the simulation results, measurements were performed with a system developed at the University of Michigan; organic liquid scintillators were used to detect the neutron emissions from the irradiation of tissue-equivalent materials. Additionally, the MPPost code was used to calculate the scintillator response from the MCNPX-PoliMi output.

Results: The simulated energy spectra and depth dose curves of the neutrons produced in different phantom materials showed similar shape. The differences of spectra and fluences between all studied materials and reference tissues were well within the achievable precision of neutron dosimetry. The shape of the simulated detector response of the liquid scintillators agreed well with measurements on the proton beamline.

Conclusion: Based on Geant4 and MCNPX-PoliMi simulations, the investigated materials appear to be suitable to study the production of neutrons in proton therapy. MC simulations were verified with neutron measurements in therapeutic proton beams.

Funding Support, Disclosures, and Conflict of Interest: This work was funded in part by the ANDANTE grant of the European Commission in the 7th Framework Program.

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