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Patient-Based Study On Characteristic Prompt Gamma-Ray Spectra Using a Prompt Gamma Imaging System During Proton Therapy

E Lee

E Lee1*, J Polf2, D Mackin3, D Dolney4, S Beddar5, S Avery6, (1) University of Pennsylvania, Philadelphia, PA, (2) Oklahoma State University, Stillwater, OK, (3) MD Anderson Cancer Center, Houston, TX, (4) University of Pennsylvania, Philadelphia, PA, (5) MD Anderson Cancer Ctr., Houston, TX, (6) University of Pennsylvania, Philadelphia, PA

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

Purpose: To demonstrate the adaptation of prompt gamma (PG) imaging for the spot scanning in a patient phantom as an independent tool for non-invasive proton beam range verification.

Methods: A cylindrical high-purity germanium (HPGe) detector was modeled using GEANT4 Monte Carlo toolkit and implemented into a modulated proton beam scanning model. Simulations were run to calculate the spectrum of energy deposited by gamma ray interactions in the modeled HPGe detector from a water phantom and a patient CT phantom during irradiations with proton beam. Images for individual spots (spot patterns were determined from a real patient treatment plan) will be reconstructed using all detected gammas as well as the gamma characteristic of specific nuclear excitations.

Results: Dose depth profiles along arbitrary lines in the beam direction showed the dependence of PG 50% falloff on the location of the dose falloff within the water phantom and the patient CT phantom. The PG energy spectra at the emission point (inside phantoms) and the detector outside phantoms were illustrated. Reconstructed gamma emission profile will be compared with dose depth profile. Prompt gamma images will be reconstructed for spot and/or treatment field.

Conclusion: This work indicated the first study of clinical implementation of the PG imaging for proton range verification using the incorporated detector response to the patient CT phantom irradiated with proton beam. The results showed feasible correlation between the spot scanning does distribution and prompt gamma ray production. This study will be used in future investigation of detector design optimization following measurements that will be carried out using custom-build prototype detector system using Compton reconstruction.

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