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Proton/Photon Beam Profile Based Isocentricity Check

R Rahimi Darabad1*, Y Yang2, P Wang3, J Fan4, (1) INOVA Schar Cancer Institute, Fairfax, VA, (2) University of Science and Technology of China, Hefei, Anhui, CN, (3) Inova Health System, Fairfax, VA, (4) Inova Health System, Fairfax, VA

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: Commercial softwares fail in processing the isocentricity check in cases of blurred beam edges caused by e.g. large lateral penumbra in clinical proton beam or large penumbra of Co60 beam in MRI linac. In this study, we use beam profiles measured for proton beams (also applicable to photon) and define the beam boundaries and the number of beam legs accordingly. The approach is different than the commercial approaches where beams borderlines are directly analyzed for determination of beam edges. Such cases generally encounter difficulties when beams are blended or the background is not significantly distinguishable, which happens so often with proton beams. In our approach, however, regardless of the background distinction and/or beams overlap, the beam legs are detected correctly since the interference is analyzed per measured profiles and is analyzed for the differences vs the absolute values.

Methods: The program is written in Matlab. Firstly, profiles are plotted along a circle that transverses all the beams. Then, the center of each beam is identified at entrance and exit. Next, a line connecting the centers is sketched to determine the beam central axis. Finally, the radius of the circle tangential to all the beam central axis is determined.


Results: We employed our software for proton beam commissioning and routine QA checks. In all studied cases, for 6D couch and PBS full gantry, with different proton energies, 70-226 MeV, the whole procedure was very smooth with results superior to commercial available softwares, to the best of our practice. We discuss on comparison with myQA, RIT and FilmQA softwares, that we have studied them all for this work.

Conclusion: The program is validated for analyzing starshot for proton in this work, and previously for all photon inclusively. Our open source program can be used by any user for beam isocentricity checks.

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