MO-FG-303-05: A Feasibility Study of Using a Cherenkov Detector Material with the Prompt Gamma Range Verification Technique in Proton Therapy

Authors


Abstract

Purpose:

To simulate the feasibility of a Cherenkov glass material for the determination of the penetration depth of therapeutic proton beams in water.

Methods:

Proton pencil beams of various energies incident onto a water phantom with dimensions of 5 × 5 × 30 cm3 were used for simulation with the Geant4 toolkit. The model used standard electromagnetic packages, packages based on binary-cascade nuclear model, several decay modules (G4Decay, G4DecayPhysics, and G4RadioactiveDecayPhysics), and optical photon components (G4OpticalPhysics). A Cherenkov glass material was modeled as the detector medium (7.2 g of In2O3 + 90 g cladding, density of 2.82 g/cm3, Zeff = 33.7, index of refraction n(600 nm) = 1.56, and energy threshold of production Eth = 156 keV ). The emitted secondary particles are analyzed characterizing their timing, energy, and angular distributions. A feasibility analysis was conducted for a simplistic detector system using this material to locate the position of the Bragg Peak.

Results:

The escaping neutrons have energies ranging from thermal to the incident proton energy and the escaping photons have energies >10 MeV. Photon peaks between 4 and 6 MeV were attributed to originate from direct proton interactions with 12C (∼ 4.4 MeV) and 1⁶O (∼ 6 MeV), respectively. The escaping photons are emitted isotropically, while low (≤10 MeV) and high (>10 MeV) neutrons are isotropic and forward-directional, respectively. The emissions of photons are categorized into prompt (∼ns) and delayed (∼min) where the prompt photons include the 4.4 and 6 MeV. The Cherenkov material had on average <2% of neutron interactions while LYSO and BGO scintillators had a minimum of ∼50%. Our simplistic detector system was capable of discerning Bragg Peak locations using a timing discrimination of ∼50 ns.

Conclusion:

We investigate the viability of using the Cherenkov material for MeV photon detection medium for the prompt gamma technique.

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