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Session: Therapy General ePoster Viewing [Return to Session]

Cross-Validation of Patient Positioning Systems Using An Optical Surface Image Guidance Platform

D Pinkham1*, S Hancock2, (1) Yale University School of Medicine, New Haven, CT, (2) Southeast Health, Cape Girardeau, MO


PO-GePV-T-386 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: Treatment delivery machines in radiation therapy are often accompanied by several supporting/complimentary subsystems for patient positioning and monitoring. During stereotactic radiation therapy procedures, these can utilize both ionizing and non-ionizing radiation to ensure that radiation is delivered accurately, often with submillimeter precision. With so many technologies at the medical physicist’s disposal, the purpose of this project is to illustrate ways that one of these technologies, optical surface image monitoring, can cross-validate the accuracy of other positioning/imaging subsystems during commissioning or routine QA.

Methods: A surface image monitoring system (C-RAD) was used to cross-validate submillimeter offsets of a CBCT registration algorithm as well as the motions effected by a corresponding 6-DOF hexapod couch. This was studied in two independent scenarios: (1) During C-RAD system commissioning, two IGRT phantoms were initially aligned to their reference CT using the hexapod, and a reference surface was captured with C-RAD. Both were subsequently misaligned over a range of clinically-relevant translations and rotations (in isolation and in combination) using prescribed offsets input directly into the hexapod system. At each misalignment step a CBCT registration was repeated and 6-DOF offsets were recorded from both the XVI system and C-RAD. (2) During hexapod couch commissioning, a Winston-Lutz cube phantom was used to confirm a relative adjustment made to the couch base using simultaneous MV imaging and C-RAD monitoring.

Results: C-RAD calculated offsets agreed with prescribed hexapod offsets with RMSE below 0.2 mm and 0.1 degrees. Similarly, C-RAD calculated offsets agreed with XVI calculated offsets with comparable RMSE. During table axis adjustment, C-RAD confirmed a 0.4mm lateral adjustment of the couch axis, agreeing with pre- and post- Winston lutz images within 0.1 mm.

Conclusion: Surface imaging, if available, can be a versatile commissioning and QA tool for other positioning systems within the radiation treatment vault.


Surface Matching, Optical Imaging, Quality Assurance


IM/TH- RT X-Ray Imaging: General (most aspects)

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