"Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it is the only thing that ever has."

Margaret Mead
Original article
peer-reviewed

A Novel Method for Quality Assurance of the Cyberknife Iris Variable Aperture Collimator



Abstract

Objective: To characterize a novel method for field-size quality assurance of a variable approximately circular aperture collimator by means of dose-area product measurements and to validate its practical use over two years of clinical application.

Methods:  To assess methodical limitations, we analyze measurement errors due to change in linac output, beam tuning, uncertainty in MU delivery, daily factors, inherent uncertainty of the large-area parallel-plate ionisation chamber, and misalignment of the large-area parallel-plate ionisation chamber relative to the primary beam axis. To establish a baseline for quality assurance, the dose-area product is measured with the large-area parallel-plate ionisation chamber for all 12 clinical iris apertures in relation to the 60 mm fixed reference aperture. To evaluate the long-term stability of the Iris collimation system, deviation from baseline data is assessed monthly and compared to a priori derived tolerance levels.

Results: Only chamber misalignment, variation in output, and uncertainty in MU delivery contribute to a combined error that is estimated at 0.2 % of the nominal field size. This is equivalent to a resolution of 0.005 mm for the 5 mm, and 0.012 mm for the 60 mm field. The method offers ease of use, small measurement time commitment, and is independent of most error sources. Over the observed period, the Iris accuray is within the tolerance levels.

Conclusions:  The method is an advantageous alternative to film quality assurance with a high reliability, short measurement time, and superior accuracy in field-size determination.



Want to read more?

Create a free account to continue reading this article.

Already a member? Login.



Original article
peer-reviewed

A Novel Method for Quality Assurance of the Cyberknife Iris Variable Aperture Collimator


Author Information

Sarah-Charlotta Heidorn Corresponding Author

Medical Physicist, European CyberKnife Center Munich

Nikolaus Kremer

Medical Physicist, European CyberKnife Center Munich

Christoph Fürweger

Chief Medical Physicist, European CyberKnife Center Munich


Ethics Statement and Conflict of Interest Disclosures

Human subjects: This study did not involve human participants or tissue. Animal subjects: This study did not involve animal subjects or tissue. Conflicts of interest: The authors have declared that no conflicts of interest exist.


Original article
peer-reviewed

A Novel Method for Quality Assurance of the Cyberknife Iris Variable Aperture Collimator


Figures etc.

Share
Original article
peer-reviewed

A Novel Method for Quality Assurance of the Cyberknife Iris Variable Aperture Collimator

  • Author Information
    Sarah-Charlotta Heidorn Corresponding Author

    Medical Physicist, European CyberKnife Center Munich

    Nikolaus Kremer

    Medical Physicist, European CyberKnife Center Munich

    Christoph Fürweger

    Chief Medical Physicist, European CyberKnife Center Munich


    Ethics Statement and Conflict of Interest Disclosures

    Human subjects: This study did not involve human participants or tissue. Animal subjects: This study did not involve animal subjects or tissue. Conflicts of interest: The authors have declared that no conflicts of interest exist.

    Acknowledgements


    Article Information

    Published: May 21, 2016

    DOI

    10.7759/cureus.618

    Cite this article as:

    Heidorn S, Kremer N, Fürweger C (May 21, 2016) A Novel Method for Quality Assurance of the Cyberknife Iris Variable Aperture Collimator. Cureus 8(5): e618. doi:10.7759/cureus.618

    Publication history

    Received by Cureus: April 03, 2016
    Peer review began: April 06, 2016
    Peer review concluded: May 20, 2016
    Published: May 21, 2016

    Copyright

    © Copyright 2016
    Heidorn et al. This is an open access article distributed under the terms of the Creative Commons Attribution License CC-BY 3.0., which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

    License

    This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Abstract

Objective: To characterize a novel method for field-size quality assurance of a variable approximately circular aperture collimator by means of dose-area product measurements and to validate its practical use over two years of clinical application.

Methods:  To assess methodical limitations, we analyze measurement errors due to change in linac output, beam tuning, uncertainty in MU delivery, daily factors, inherent uncertainty of the large-area parallel-plate ionisation chamber, and misalignment of the large-area parallel-plate ionisation chamber relative to the primary beam axis. To establish a baseline for quality assurance, the dose-area product is measured with the large-area parallel-plate ionisation chamber for all 12 clinical iris apertures in relation to the 60 mm fixed reference aperture. To evaluate the long-term stability of the Iris collimation system, deviation from baseline data is assessed monthly and compared to a priori derived tolerance levels.

Results: Only chamber misalignment, variation in output, and uncertainty in MU delivery contribute to a combined error that is estimated at 0.2 % of the nominal field size. This is equivalent to a resolution of 0.005 mm for the 5 mm, and 0.012 mm for the 60 mm field. The method offers ease of use, small measurement time commitment, and is independent of most error sources. Over the observed period, the Iris accuray is within the tolerance levels.

Conclusions:  The method is an advantageous alternative to film quality assurance with a high reliability, short measurement time, and superior accuracy in field-size determination.



Want to read more?

Create a free account to continue reading this article.

Already a member? Login.



Sarah-Charlotta Heidorn

Medical Physicist, European CyberKnife Center Munich

For correspondence:
sarah.heidorn@cyber-knife.net

Nikolaus Kremer

Medical Physicist, European CyberKnife Center Munich

Christoph Fürweger, Ph.D.

Chief Medical Physicist, European CyberKnife Center Munich

Sarah-Charlotta Heidorn

Medical Physicist, European CyberKnife Center Munich

For correspondence:
sarah.heidorn@cyber-knife.net

Nikolaus Kremer

Medical Physicist, European CyberKnife Center Munich

Christoph Fürweger, Ph.D.

Chief Medical Physicist, European CyberKnife Center Munich