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Design and Geometric Validation of An Externally and Internally Deformable, Programmable Lung Motion Phantom

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Y Cheung

Y Cheung*, A Sawant, UT Southwestern Medical Center, Dallas, TX


SU-C-BRF-5 Sunday 1:00PM - 1:55PM Room: Ballroom F

Most clinically-deployed strategies for respiratory motion management in lung radiotherapy (e.g., gating, tracking) use external markers that serve as surrogates for tumor motion. However, typical lung phantoms used to validate these strategies are rigid-exterior+rigid-interior or rigid-exterior+deformable-interior. Neither class adequately represents the human anatomy, which is deformable internally as well as externally. We describe the construction and experimental validation of a more realistic, externally- and internally-deformable, programmable lung phantom.

The outer shell of a commercially-available lung phantom (RS-1500, RSD Inc.) was used. The shell consists of a chest cavity with a flexible anterior surface, and embedded vertebrae, rib-cage and sternum. A 3-axis platform was programmed with sinusoidal and six patient-recorded lung tumor trajectories. The platform was used to drive a rigid foam “diaphragm” that compressed/decompressed the phantom interior. Experimental characterization comprised of mapping the superior-inferior (SI) and anterior-posterior (AP) trajectories of external and internal radioopaque markers with kV x-ray fluoroscopy and correlating these with optical surface monitoring using the in-room VisionRT system.

The phantom correctly reproduced the programmed motion as well as realistic effects such as hysteresis. The reproducibility of marker trajectories over multiple runs for sinusoidal as well as patient traces, as characterized by fluoroscopy, was within 0.4 mm RMS error for internal as well as external markers. The motion trajectories of internal and external markers as measured by fluoroscopy were found to be highly correlated (R=0.97). Furthermore, motion trajectories of arbitrary points on the deforming phantom surface, as recorded by the VisionRT system also showed a high correlation with respect to the fluoroscopically-measured trajectories of internal markers (R=0.92).

We have developed a realistic externally- and internally-deformable lung phantom that will serve as a valuable tool for clinical QA and motion management research. This work was supported through funding from the NIH and VisionRT Ltd.

Funding Support, Disclosures, and Conflict of Interest: Amit Sawant has research funding from Varian Medical Systems, VisionRT and Elekta

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