TH‐D‐M100J‐05: A Phantom and Software Analysis Tool for Quality Assurance (QA) of LINAC with Onboard KV X‐Ray Imaging Device

W. Mao, L. Xing

Research output: Contribution to journalArticle


Purpose: LINAC with integrated kV imaging device is emerging as an important clinical tool for radiation therapy. A novel strategy is developed to examine the system geometric and mechanical accuracies to ensure the adequate use of this new technology. Method and Materials: Three major issues that are crucial to the performance of the LINAC with onboard imager are in mind when designing the phantom system: (1) the coincidence of kV and MV beam isocenters; (2) the positional accuracy of kV and MV X‐ray sources; and (3) the positional and directional accuracy of the kV and MV imagers. After a computer simulation to maximize the detection sensitivity of these three sets of parameters, a QA phantom was built by placing 13 ball bearings (BBs) on the surface of the rectangular phantom (18×18×20 cm). A Varian Trilogy was used to validate the QA system design. The kV and MV projection data were collected with gantry rotating over 360°. The software analysis tool then computes those three sets of parameters by comparing the measured and predicted BB locations on each projection. Results: The performance of the QA package was assessed by intentionally introducing a number of errors. As a result, our QA system showed great sensitivity and accuracy in error detection. Specifically, it was found that the accuracy of the system in detecting angular uncertainties of the kV/MV sources was better than 0.2°. For spatial uncertainties, such as the kV/MV iso‐center mis‐alignment, the source position, or the detector position, the demonstrated accuracy was better than 1 mm. Furthermore, the system was able to reveal any combinational error of the angular and spatial variables at any gantry angle. Conclusions: Iso‐centers, source positions, and imager positions and directions for kV and MV can be examined accurately with this QA system.

Original languageEnglish (US)
Number of pages1
JournalMedical Physics
Issue number6
Publication statusPublished - 2007


ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging

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