Application of multi-leaf collimator quality assurance phantom on Truebeam

Abstract

Objective To perform a routine quality assurance procedure for Truebeam multi-leaf collimator (MLC) using MLC quality assurance (QA) phantom, verifying the reliability of MLC during the treatment. Methods MLC QA phantom was a specialized phantom for multi-leaf collimator QA, and contained five radio-opaque spheres that were embedded in an L-shape. The phantom was placed isocentrically on the Truebeam treatment couch for the tests. A quality assurance plan was settled up in the Eclipse v10.0 so that the fields for acquiring the necessary images could be created. The images were acquired by the electronic portal imaging device (EPID), and imported into the PIPSpro software for the analysis. The tests were delivered once a week for six weeks to verify consistency of the delivery, and the images were acquired in the same manner each time. Results For the leaf position test, the average position error was (0.21±0.02) mm. The leaf width was measured at the isocenter, and the average error was (0.04±0.02) mm for the leaf width test. Multi-Port test showed the dynamic leaf shift error, the average error was (0.26±0.04) mm. For the leaf transmission test, the average inter-leaf leakage value was 1.0%±0.14%. Conclusions The MLC system of Truebeam could operate very well and the QA phantom is a useful test tool for the MLC QA. Key words: Truebeam linear accelerator; Multi-leaf collimator; Quality assurance