SU-E-T-184: LINAC Commissioning Measurements Utilizing the Cylindrical Arc Check Phantom.

Abstract

New devices for IMRT and VMAT QA are continually becoming available. Despite the availability of these devices they are underutilized for routine mechanical QA. In this work we take advantage of the cylindrical geometry of the Arc Check phantom to perform tests that are an integral part of commissioning and routine QA. The Arc Check is a cylindrical phantom with a diameter of 26.59cm and a 1386 diode array arranged on a cylindrical plane. Owing to its cylindrical design it is capable of measuring entry and exit radiation. For this experiment the Arc Check was set up using the mechanical pointer at 86.7cm SSD. The device was leveled using its inclinometer and was properly rotated to align with the lasers and cross-hair. With the phantom set up at the expected isocenter of the LINAC, 100MUs with a 10×10 field were delivered at different gantry angles, couch and collimator rotations. Each delivery was recorded individually and for each one the radiation center at the entry and exit levels of the detector were estimated. That provided the path of the radiation center through the device. The radiation path was reconstructed for each rotation individually and the coincidence of the mechanical and radiation isocenter was evaluated. A procedure and MATLAB routine were developed that accepted as input the text files that are the output of the Arc Check measurement and geometrically reconstructed in 3-dimensions the isocenter and radiation central axis for each rotation. The coincidence of the radiation and mechanical isocenter was verified. This work demonstrates that by utilizing the geometry of a commercially available device multiple mechanical LINAC tests that are part of routine QA can be evaluated in one single setup.