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

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.