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Imaging of Prompt Gamma Rays Emitted During Delivery of Clinical Proton Beams with a Compton Camera: Feasibility Studies for Range Verification

J Polf

J Polf1*, S Avery2 , D Mackin3 , S Beddar3 , (1) University of Maryland School of Medicine, Baltimore, MD, (2) UNIVERSITY OF PENNSYLVANIA, Philadelphia, PA, (3) UT MD Anderson Cancer Center, Houston, TX


WE-EF-303-7 (Wednesday, July 15, 2015) 1:45 PM - 3:45 PM Room: 303

Purpose: Evaluation of a prototype Compton camera (CC) for imaging prompt gamma rays (PG) emitted during clinical proton beam irradiation for in vivo beam range verification.

Methods: We irradiated a water phantom with 114 MeV and 150 MeV proton pencil beams at clinical beam currents ranging from 1 nA up to 5 nA. The CC was placed 15 cm from the beam central axis and PGs from 0.2 MeV up to 6.5 MeV were measured during irradiation. From the measured data, 2-dimensional (2D) PG images were reconstructed. One-dimensional (1D) profiles from the PG images were compared to measured depth dose curves.

Results: The CC was able to measure PG emission during delivery of both a single 150 MeV pencil beam and a 5 cm x 5 cm mono-energetic layer of 114 MeV pencil beams. From the 2D images, a strong correlation was seen between the depth of the distal falloff of PG emission and the Bragg peak (BP). 1D profiles extracted from the PG images show that the distal 60% falloff of the PG emission lined up well with the distal 90% of the BP. Shifts as small as 3 mm in the beam range could be detected on both the 2D PG images and 1D profiles with an uncertainty of 1.5 mm. With the current CC prototype, a minimum dose delivery of 400 cGy was required to produce usable PG images.

Conclusions: It was possible to measure and image PG emission with our prototype CC during proton beam delivery and to detect shifts in the BP range in the images. Therefore prompt gamma imaging with a CC for the purpose of in vivo range verification is feasible. However, for the studied system improvements in detector efficiency and reconstruction algorithms are necessary to make it clinically viable.

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