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Polarization-Based Coincidence Discrimination for Compton-PET in Proton Therapy Range Verification

A Makarova

A Makarova1*, H Shirato1,2 , K Umegaki1,3 , L Xing4 , H Peng4 , (1) Global Station for Quantum Medical Science and Engineering, Global Institution for Collaborative Research and Education, Hokkaido University, Sapporo, Hokkaido, (2) Department of Radiation Medicine, Graduate School of Medicine, Hokkaido University, Sapporo, Hokkaido, (3) Division of Quantum Science and Engineering, Faculty of Engineering, Hokkaido University, Sapporo, Hokkaido, (4) Department of Radiation Oncology, Stanford University, Palo Alto, CA


SU-I-GPD-J-46 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: One challenge of PET imaging is its limited photon detection sensitivity. The dependence of Compton scattering angle on the orthogonal polarization of two annihilation gammas can be utilized to enhance the sensitivity and thus increase image signal-to-noise ratio (SNR) up to 22% (Toghyani, M., et al. "Polarisation-based coincidence event discrimination: an in silico study towards a feasible scheme for Compton-PET." Physics in Medicine and Biology 61(15), p. 5803 - 5817). In this study we investigate potential use of this approach for the range verification in proton therapy with Geant4 - based modeling.

Methods: The G4PolarizedComptonModel was selected as the model which uses Stokes vector for polarization. The figure presents the correlation of azimuthal Compton scattering angles for the annihilation photons modeled with Geant4.To receive the PET image of proton beam in water the concentration of positron emitters was recorded in each voxel in phantom. First, the basic PET installation was modeled in GAMOS. The code was added so that the polarization of photons is used for coincidence detection. Secondly, the Compton camera system will be modeled using the new addition to GAMOS framework.

Results: The two PET images with and without polarization information are reconstructed and compared for generic PET installation for the proof of concept. After that, modeling of Compton - PET will allow to measure the scattering angles of particles similar to real-life installation and investigate the impact of the new technique on the precision of range measurement.

Conclusion: Usage of the orthogonal polarizations of annihilation pairs in PET inexplicitly via measurement of the azimuthal angles of Compton scattering is a promising way to increase the output signal and spatial resolution.

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