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Proton Therapy Range Verification Using Prompt Gamma Rays: 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

MO-G-137-1 Monday 5:15PM - 6:00PM Room: 137

Purpose: To simulate a coincidence detector system for in vivo range verification using prompt gamma (PG) emission technique for proton radiation therapy and to compare the results with the alternative technique utilizing the positron-emitting nuclei (PEN).

Methods: A coincidence detector system for characterizing both emitted and registered prompt gamma spectrum was simulated by Geant4 Monte Carlo toolkit version 9.4.9 p02. The interaction of 110 MeV protons with target phantom of PMMA (5 cm x 5 cm x 50 cm) was used in the simulation. A virtual detector (5 cm x 5 cm x 1 mm) was replicated 500 times to form a bank of detectors. A lower bank was placed 1 cm above the phantom while another bank was placed 1 cm above the lower bank. A coincidence requirement was met when a gamma had passed through both a bottom detector segment and the corresponding top detector segment directly above it. Our investigation used the built-in physics list consisting of electromagnetic as well as nuclear interactions.

Results: The depths corresponding to the maximum prompt gamma counts were found to be in close proximity to the range of protons as determined by the Bragg Peak. We noted that the PEN yields had their maximum and distal 50% yield more superficially than the Bragg Peak. This is clearly different compared to PG yields that showed their maximum in closer proximity to the Bragg Peak. The 50% distal PEN yields also lied shallower to the Bragg peak whereas the 50% distal PG yields lied deeper with respect to the Bragg Peak.

Conclusion: This work shows clearly that the range of the incident protons can be measured in vivo via a suitable detector system utilizing the PG technique. More realistic simulations by implementing and optimizing various detector materials are now being planned.

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