Evaluating the Efficacy of Machine Performance Checks as an Alternative to Winston-Lutz Quality Assurance Testing in the TrueBeam Linear Accelerator with HyperArc.

HyperArc is a preferred technique for treating brain metastases, employing a single isocenter for multiple lesions. Geometrical isocentricity in the TrueBeam linear accelerator with HyperArc is crucial. We evaluated machine performance checks (MPCs) as an alternative to the Winston-Lutz (WL) test to verify the treatment isocenter. Between January and July 2023, we assessed 53 data points using MPC and Winston-Lutz tests. The isocenter size obtained from the MPC and its sum, including the rotation-induced couch shift, were compared with the maximum total delta value from the Winston-Lutz test. The maximum total delta was 0.68 ± 0.10 mm, while the isocenter size was 0.28 ± 0.02 mm. The sum of the isocenter size and rotation-induced couch shift measured by MPC was 0.61 ± 0.03 mm. During the Winston-Lutz test (without couch rotation), the maximum total delta value was 0.56 ± 0.13 mm. A t-test analysis revealed a significant difference in the isocenter size averages between the Winston-Lutz and MPC outcomes, whereas the Pearson's correlation coefficient yielded no correlation. Our study highlights the necessity for separate MPC and Winston-Lutz tests for isocenter verification. Therefore, the Winston-Lutz test should precede stereotactic radiosurgery for isocenter verification.

Application of multi-leaf collimator quality assurance phantom on Truebeam / 中华放射医学与防护杂志

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.