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A Simulation Study with Geant4 Investigating the Secondary Prompt Gamma Emissions From Incident 40 MeV Protons Onto Various Materials

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A lau

A lau*, Y Chen, S Ahmad, Oklahoma Univ. Health Science Ctr., Oklahoma City, OK

SU-E-T-302 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: This study aims to investigate the prompt secondary gamma spectrum and the
depth-dose distributions of incident 40 MeV protons onto various phantom materials.
The goal is to find a relationship between the secondary prompt gamma emissions and
the range of the incident particles.

Methods: An application was constructed using the Geant4 Monte Carlo
Toolkit utilizing various physics packages. Several phantom materials were irradiated
with a pencil beam of 40 MeV protons. These materials include PMMA (C5H8O2,
density 1.18 g/cm³) and the built-in Geant4 materials bone, soft-tissue, and water. For
each simulation, the energy deposited from the incident proton was recorded every 1 mm
increment of depth in the phantom. The resulting prompt secondary gamma emissions
were recorded from 0 to 10 MeV in energy bins of 10 keV.

Results: The secondary prompt gamma spectrum has various peaks. The peaks located
about 4.4 and 6 MeV correspond to the carbon and oxygen de-excitation photons,
respectively. Our simulations show greater production of the higher-energy gamma
particles closer to the Bragg-Peak. When we plot the oxygen peak against the normalized
Bragg-Peak we found that in all materials the difference between Bragg-Peak and the
oxygen de-excitation photon peak to be about 2 mm. The oxygen peak could be used in
the clinic for range verification of the incident proton beam.

Conclusions: Our Geant4 Monte Carlo application was used to investigate the secondary
prompt gamma emissions from incident 40 MeV protons. A relationship was between
the 6 MeV peak and the incident proton Bragg Peak. We believe that prominent peaks
around 4 and 6 MeV can be used to locate the range of the incident beam provided a
detector system is built that can count these high-energy gamma particles.

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