(Saturday, 4/7/2018)
Room: Foyer
Purpose: To assess the accuracy of 6 Degrees of Freedom (6DOF) couch for patient positioning in bothVarian and Elekta platforms using a custom developed phantom that can be used for dailyquality assurance.
Methods: An 80mm acrylic cube with implanted titanium markers at known off set distances and eight aluminum wire markers 2mm X 10 mm in diameter set in 2 rows that project on CBCT sliceswas used in this study. The cube was mounted on a novel platform that was precisely milledusing a computerized numerical control (CNC) milling machine so that the cube is warped 2.5degrees in each of the rotational axis ( Pitch, Roll and Yaw).CBCT images were acquired in both Varian True Beam and Elekta Versa linacs and analyzedusing the vendor supplied software. The 6DOF couch was adjusted based on the alignment ofmarkers and aluminum wires embedded in the acrylic cube.
Results: The baseline tilt accuracy of the CT and Linear accelerator couch was verified using a digital level and dual axis protractor. With the phantom precisely mounted on the platform with known rotationaloffsets, translational and rotational measurements were performed with a PerfectPitch (Varian)and Hexapod (Elekta). We achieved an alignment accuracy of 0.2 mm and 0.2 degree on bothplatforms
Conclusion: We have validated a custom developed phantom that can be used for quick and robust daily QAof 6DOF couches to ensure accurate patient positioning in highly conformal treatments. Thecurrent QA device can test the performance of the 6DOF couch on a True Beam (version 2.0)and Elekta Hexapod couches with an alignment accuracy of 0.2mm and 0.2 degree. Thisphantom has been integrated as part of daily QA on our Linear accelerators.
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