Feasibility of an In-House Phantom for Mechanical and Geometrical QA

We designed an in-house phantom for mechanical quality assurance (QA) and compared its performance against commercial available QA tools. The QA phantom is an acrylic cubic shape with dimensions of 150 mm × 150 mm × 150 mm, and with a pocket into which various adapter plates can be inserted. The plates were classified into three types (A, B, and C) according to their location and shape. An additional accessory can be used to check the alignment of lasers to the center of CT image scans. We evaluated the usefulness of the phantom by checking mechanical isocentricity, field size accuracy, isocenter and position coincidence between the treatment beam and the image guidance systems, and alignment of the lasers. All the tests carried out were within the tolerance limits. The isocenter of the gantry and collimator was within 1 mm and the field size was within 2 mm for both the commercial tool and the new phantom. The kV image of the isocenter was within 0.5 mm for both the commercial tool and the new phantom and that of the displacement of the off-center position from the isocenter was within 0.5 mm for both phantoms. Displacement between the laser origin and the center of a CT image scan was within 0.5 mm for the commercial tool and new phantom. The developed phantom can also be used to easily check the geometrical and mechanical parameters of medical linear accelerators (LINAC) and CT simulators.