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A Novel and Comprehensive Daily QA Tool Using EPID and KV Imagers


B Sun

B Sun1*, S Yaddanapudi2, D Yang3, H Li4, S Mutic5, S Goddu6, (1) Washington Univ. in St. Louis, St. Louis, MO, (2) Washington University in St. Louis, St. Louis, MO, (3) Washington University in St Louis, St Louis, MO, (4) Washington University School of Medicine, Saint Louis, MO, (5) Washington University School of Medicine, Saint Louis, MO, (6) Washington University, St. Louis, MO

WE-E-141-4 Wednesday 2:00PM - 3:50PM Room: 141

Purpose: As treatment delivery is becoming more and more complex, there is a pressing need for robust QA tools to improve efficiency and comprehensiveness. This work aims to present the hardware and software tools developed for comprehensive QA of LINAC using EPID and kV imagers.

Methods: Daily QA phantom, that includes a horizontal MV-phantom for QA MV-beams and a vertical kV-phantom for testing kV-imaging (OBI) system, hangs from the gantry to test both geometric and dosimetric components of the LINAC and the OBI. The MV phantom consists of a solid water block incorporating 11 circular steel plugs for dose measurements at multiple depths and resolution plug for MV-image quality. The kV-phantom consists of a Leeds phantom for testing the low contrast and high contrast resolutions of the kV-imager. On Varian TrueBeam machines the QA is automated to acquire MV and kV-portals for each modality and software tools were developed for simultaneously analyzing these images. Traditional QA parameters, such as output, flatness, symmetry, TPR20/10, and positional accuracy of the jaws and MLCs, were derived from these measurements. A QA report is automatically generated for physicist review and saved to a database. The QA tools were tested on a TrueBeam machine over two months and further validated on a detuned 6 MV beam by introducing errors in output, symmetry, energy and MLC positions.

Results:Machine output constancy, compared against a calibrated ion-chamber, shown to be within ±0.5% and the beam symmetry deviations of 1% can be detected. As expected, TPR20/10 is less sensitive to energy changes when compared to beam flatness. MLC position errors of 0.5mm can be detected. The field size and phantom positioning accuracy can be determined within 0.5 mm.

Conclusion:The EPID and kV imagers based QA tool has proved to be an efficient and thorough method in checking LINAC performance.

Funding Support, Disclosures, and Conflict of Interest: This work is partially supported by Varian Medical System.

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