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Evaluation of a Ceramic-Centered Phantom for QA of a 6 Degree-Of-Freedom Couch

G Owen

G Owen*, J Keller , A Harrison , P Florio , D To , Y Yu , P Charpentier , Thomas Jefferson University, Philadelphia, PA


SU-I-GPD-J-19 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To validate the ISO Cube™ phantom use for the Elekta HexaPOD evo RT System positional accuracy following TG-142 guidelines and comparison to current clinical phantom.

Methods: Phantom shifts were performed from predetermined translational offset with an induced 1 degree rotation along the z-axis. The initial cone-beam CT (CBCT) of the phantom using the Elekta XVI (Fast Head and Neck) protocol and the clipbox autoregistration algorithm produce a fusion between the local and reference images. Positional shifts were made with the Elekta HexaPOD evo RT System to align the phantom at isocenter. A second CBCT was taken to determine the positional accuracy of the initial shifts. A clinical physicist performed this procedure on both the ISO Cube™ and the QUASAR™ Penta-Guide phantoms and final positional shifts were recorded for ten setups over multiple days.

Results: Over the course of ten iterations, the final translational shift averages for the ISO Cube™ are 0.18+/-0.06, 0.08+/-0.06, and 0.07+/-0.09 mm in the x, y, and z directions with angular rotations of 0.29+/-0.06, 0.31+/-0.03, and 0.15+/-0.08 degree along the x, y, and z axes. The QUASAR™ Penta-Guide translational shift averages are 0.26+/-0.14, 0.20+/-0.17, and 0.58+/-0.30 mm in the x, y, and z directions with angular rotations of 0.14+/-0.05, 0.36+/-0.08, and 0.25+/-0.07 degree along the x, y, and z axes.

Conclusion: As a daily QA phantom, the ISO Cube™ in conjunction with the XVI autoregistartion algorithm provides verification of the necessary submillimeter accuracy for CBCT positioning recommended by TG-142 guidelines for linear accelerators performing SRS/SBRT treatment necessary for the Elekta HexaPOD evo RT System. Compared to the QUASAR™ Penta-Guide, the ISO Cube™ has an overall lower average translational shifts and standard deviations increasing consistency in QA results and allows institutional policies invoking tighter tolerances for cone-beam positional accuracy.

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