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Emission of Secondary Particles From a PMMA Phantom During Proton Irradiation: A Simulation Study with the Geant4 Monte Carlo Toolkit

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A Lau

A Lau*, Y Chen , S Ahmad , University of Oklahoma Health Sciences Ctr., Oklahoma City, OK


SU-E-T-519 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Proton therapy exhibits several advantages over photon therapy due to depth-dose distributions from proton interactions within the target material. However, uncertainties associated with protons beam range in the patient limit the advantage of proton therapy applications. To quantify beam range, positron-emitting nuclei (PEN) and prompt gamma (PG) techniques have been developed. These techniques use de-excitation photons to describe the location of the beam in the patient. To develop a detector system for implementing the PG technique for range verification applications in proton therapy, we studied the yields, energy and angular distributions of the secondary particles emitted from a PMMA phantom.
Methods: Proton pencil beams of various energies incident onto a PMMA phantom with dimensions of 5 x 5 x 50 cm3 were used for simulation with the Geant4 toolkit using the standard electromagnetic packages as well as the packages based on the binary-cascade nuclear model. The emitted secondary particles are analyzed.
Results: For 160 MeV incident protons, the yields of secondary neutrons and photons per 100 incident protons were ~6 and ~15 respectively. Secondary photon energy spectrum showed several energy peaks in the range between 0 and 10 MeV. The energy peaks located between 4 and 6 MeV were attributed to originate from direct proton interactions with 12C (~ 4.4 MeV) and 16O (~ 6 MeV), respectively. Most of the escaping secondary neutrons were found to have energies between 10 and 100 MeV. Isotropic emissions were found for lower energy neutrons (<10 MeV) and photons for all energies, while higher energy neutrons were emitted predominantly in the forward direction. The yields of emitted photons and neutrons increased with the increase of incident proton energies.
Conclusions: A detector system is currently being developed incorporating the yields, energy and angular distributions of secondary particles from proton interactions obtained from this study.

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