Room: AAPM ePoster Library
Purpose: establish a simple workflow for the daily QA of a 6-degrees-of freedom (6DOF) treatment table by applying a known transformation matrix on a straight-aligned CT image of the Daily QA phantom.
Methods: Quasar Penta-Guide phantom was CT scanned with 0° rotations (yaw, pitch, roll) using the CT scanner laser alignment. Before loading the images into the treatment planning system, a transformation matrix with 1.5° of roll, pitch and yaw was digitally applied to the image matrix. All image preprocessing steps were done in the 3D Slicer platform. The transformed image was used to create a daily QA plan containing 3 set-up fields: CBCT and orthogonal KVs. The Penta-Guide phantom was then acquired using CBCT with a known translation shift, and registered to the transformed planning image to obtain the measured translation, roll, pitch and yaw estimates. The pre- and post-alignment orthogonal KV images were used to verify that the planned iso-center was within 2mm of the machine iso-center after the alignment.
Results: was performed on the Varian TrueBeam OBI software using automated registration between the planning CT and CBCT to minimize user dependent registration errors. The preset values for translation and rotation were: vertical 1.2 cm, lateral 1.0 cm, longitudinal -1.4 cm, roll 1.5°, pitch 1.5° and yaw 1.5°. After the alignment, the overall uncertainty of the measured translational and rotational values were below 1mm and 0.1° and the iso-center was within 1mm of the original positioning.
Conclusion: proposed simplified workflow is capable of accurately assessing the rotational estimates of the 6DOF treatment table on a daily basis without the need for additional devices. Implementing this method will not increase the time to perform daily QA, as the registration of the transformed phantom will provide the verification of the 6DOF in a single acquisition.