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Real-Time Visualization of Discrete Spot Scanning Proton Therapy Beam for Quality Assurance

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Y Matsuzaki

Y Matsuzaki1*, C Jenkins2 , Y Yang2 , T Yoshimura3 , Y Fujii3 , K Umegaki4 , L Xing2 , (1) Proton Beam Therapy Center, Hokkaido University Hospital, Sapporo, Hokkaido, (2) Stanford University, Stanford, California, (3) Hokkaido University Graduate School of Medicine, Sapporo, Hokkaido, (4) Global Institution for Collaborative Research and Education (GI-CoRE), Hokkaido University, Sapporo, Hokkaido


TU-FG-BRB-12 (Tuesday, August 2, 2016) 1:45 PM - 3:45 PM Room: Ballroom B

Purpose: With the growing adoption of proton beam therapy there is an increasing need for effective and user-friendly tools for performing quality assurance (QA) measurements. The speed and versatility of spot-scanning proton beam (PB) therapy systems present unique challenges for traditional QA tools. To address these challenges a proof-of-concept system was developed to visualize, in real-time, the delivery of individual spots from a spot-scanning PB in order to perform QA measurements.

Methods: The PB is directed toward a custom phantom with planar faces coated with a radioluminescent phosphor (Gd2O2s:Tb). As the proton beam passes through the phantom visible light is emitted from the coating and collected by a nearby CMOS camera. The images are processed to determine the locations at which the beam impinges on each face of the phantom. By so doing, the location of each beam can be determined relative to the phantom. The cameras are also used to capture images of the laser alignment system. The phantom contains x-ray fiducials so that it can be easily located with kV imagers. Using this data several quality assurance parameters can be evaluated.

Results: The proof-of-concept system was able to visualize discrete PB spots with energies ranging from 70 MeV to 220 MeV. Images were obtained with integration times ranging from 20 to 0.019 milliseconds. If not limited by data transmission, this would correspond to a frame rate of 52,000 fps. Such frame rates enabled visualization of individual spots in real time. Spot locations were found to be highly correlated (R²=0.99) with the nozzle-mounted spot position monitor indicating excellent spot positioning accuracy

Conclusion: The system was shown to be capable of imaging individual spots for all clinical beam energies. Future development will focus on extending the image processing software to provide automated results for a variety of QA tests.

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