SU‐E‐T‐234: Daily Quality Assurance for a Six Degrees of Freedom Couch Using a Novel Phantom

Abstract

Purpose:To test the accuracy and reproducibility of both translational and rotational movements for a couch with six degrees of freedom (6DoF) using a novel phantom designMethods:An end‐to‐end test was carried out using two different phantoms. A 6 cm3 cube with a central fiducial BB (WL‐QA Sun Nuclear) and a custom fabricated rectangular prism (31 cm × 8 cm × 8 cm), placed on a baseplate with known angular offsets for pitch, roll and yaw with a central fiducial BB and unique surface structures for registration purposes, were used. The end‐to‐end test included an initial CT simulation for a reference study, setup to an offset mark on each phantom, registration of the reference CT to the acquired cone‐beam CT, and final Winston‐Lutz delivery at four cardinal gantry angles. Results for both translational and rotational movements were recorded and compared for both phantoms.Results:Translational and rotational measurements were performed with a PerfectPitch (Varian) couch for 10 trials for both phantoms. Distinct translational shifts were [−5.372±0.384mm, −10.183±0.137mm, 14.028±0.155mm] for the cube and [7.520±0.159mm, −9.117±0.101mm, 16.273±0.115mm] for the prototype phantom for lateral, longitudinal, and vertical shifts, respectively. Distinct rotational adjustments were [1.121±0.102o, −1.067±0.235o, −2.662±0.380o] for the cube and [2.534±0.059o, 1.994±0.025o, 2.094±0.076o] for the prototype for pitch, roll, and yaw, respectively. Winston‐Lutz test results performed after 6DoF couch correction from each cardinal gantry angle ranged from 0.26–0.72mm for the cube and 0.55–0.86mm for the prototype.Conclusion:The prototype phantom is more precise for both translational and rotational adjustments compared to a commercial phantom. The design of the prototype phantom allows for a more discernible visual confirmation of correct translational and rotational adjustments with the prototype phantom. Winston‐Lutz results are more accurate for the commercial phantom but are still within tolerance for the prototype phantom.