Evaluation of an improved picket fence style test for routine MLC positional QA.

IF 2 4区 医学 Q3 RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING
Michael Barnes, Therese Standen, Renee Blackmore, Peter Greer
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引用次数: 0

Abstract

Purpose: The aim was to develop and evaluate an EPID-based MLC positional test that addresses known weaknesses of the picket fence test and has sufficient accuracy so that the AAPM MPPG 8.b. MLC position action limit of ± 0.5 mm can be implemented.

Methods: Weaknesses and inaccuracies in the picket fence test were identified and a new test plan and analysis algorithm named stakitt was developed. Stakitt was evaluated for repeatability and for sensitivity on the Varian TrueBeam linac with both Millennium MLC and HDMLC and on a Varian Clinac with Millennium MLC. Sensitivity was tested via deliberate introduction of errors into the test plan of magnitude: ± 0.1, ± 0.5, ± 1.0 and ± 1.5 mm. Measured sensitivity was compared to published sensitivity of the picket fence test. Additionally, a use case was presented based on results from a TrueBeam linac to highlight the effect of MLC backlash on MLC positions at non-zero gantry angles.

Results: Repeatability was observed to within 0.04 mm (3 SD) with the TrueBeams being more repeatable than the Clinac. The deliberately introduced errors were accurately measured to within 0.28 mm and were comparable to the traditional picket fence. Reduced accuracy was recorded for the HDMLC small leaves, which was attributed to an apparent variation in measured leaf width across the range of travel, which impacted the measurement of the leaf tip position. The clinical use case demonstrated variability in MLC leaf positions between gantry 90° and gantry 270° that were of the magnitude of the MLC backlash.

Conclusion: The stakitt test addresses the weaknesses of the picket fence test and has accuracy appropriate for implementation of a ± 0.5 mm action limit. However, such an action limit may not be currently practical at non-zero gantry angles due to the impact of MLC leaf backlash.

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来源期刊
CiteScore
3.60
自引率
19.00%
发文量
331
审稿时长
3 months
期刊介绍: Journal of Applied Clinical Medical Physics is an international Open Access publication dedicated to clinical medical physics. JACMP welcomes original contributions dealing with all aspects of medical physics from scientists working in the clinical medical physics around the world. JACMP accepts only online submission. JACMP will publish: -Original Contributions: Peer-reviewed, investigations that represent new and significant contributions to the field. Recommended word count: up to 7500. -Review Articles: Reviews of major areas or sub-areas in the field of clinical medical physics. These articles may be of any length and are peer reviewed. -Technical Notes: These should be no longer than 3000 words, including key references. -Letters to the Editor: Comments on papers published in JACMP or on any other matters of interest to clinical medical physics. These should not be more than 1250 (including the literature) and their publication is only based on the decision of the editor, who occasionally asks experts on the merit of the contents. -Book Reviews: The editorial office solicits Book Reviews. -Announcements of Forthcoming Meetings: The Editor may provide notice of forthcoming meetings, course offerings, and other events relevant to clinical medical physics. -Parallel Opposed Editorial: We welcome topics relevant to clinical practice and medical physics profession. The contents can be controversial debate or opposed aspects of an issue. One author argues for the position and the other against. Each side of the debate contains an opening statement up to 800 words, followed by a rebuttal up to 500 words. Readers interested in participating in this series should contact the moderator with a proposed title and a short description of the topic
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