SU-E-T-269: Differential Hazard Analysis For Conventional And New Linac Acceptance Testing Procedures

Authors

  • Harry T,

    1. Oregon State University, Corvallis, OR
    2. Washington University School of Medicine, Saint Louis, MO
    3. Washington University in St. Louis, St. Louis, MO
    4. Washington University, St. Louis, MO
    5. Washington University, St. Louis, MO
    6. Washington University School of Medicine, Saint Louis, MO
    7. UCSD Medical Center, La Jolla, CA
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  • Yaddanapudi S,

    1. Oregon State University, Corvallis, OR
    2. Washington University School of Medicine, Saint Louis, MO
    3. Washington University in St. Louis, St. Louis, MO
    4. Washington University, St. Louis, MO
    5. Washington University, St. Louis, MO
    6. Washington University School of Medicine, Saint Louis, MO
    7. UCSD Medical Center, La Jolla, CA
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  • Cai B,

    1. Oregon State University, Corvallis, OR
    2. Washington University School of Medicine, Saint Louis, MO
    3. Washington University in St. Louis, St. Louis, MO
    4. Washington University, St. Louis, MO
    5. Washington University, St. Louis, MO
    6. Washington University School of Medicine, Saint Louis, MO
    7. UCSD Medical Center, La Jolla, CA
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  • Goddu S,

    1. Oregon State University, Corvallis, OR
    2. Washington University School of Medicine, Saint Louis, MO
    3. Washington University in St. Louis, St. Louis, MO
    4. Washington University, St. Louis, MO
    5. Washington University, St. Louis, MO
    6. Washington University School of Medicine, Saint Louis, MO
    7. UCSD Medical Center, La Jolla, CA
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  • Noel C,

    1. Oregon State University, Corvallis, OR
    2. Washington University School of Medicine, Saint Louis, MO
    3. Washington University in St. Louis, St. Louis, MO
    4. Washington University, St. Louis, MO
    5. Washington University, St. Louis, MO
    6. Washington University School of Medicine, Saint Louis, MO
    7. UCSD Medical Center, La Jolla, CA
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  • Mutic S,

    1. Oregon State University, Corvallis, OR
    2. Washington University School of Medicine, Saint Louis, MO
    3. Washington University in St. Louis, St. Louis, MO
    4. Washington University, St. Louis, MO
    5. Washington University, St. Louis, MO
    6. Washington University School of Medicine, Saint Louis, MO
    7. UCSD Medical Center, La Jolla, CA
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  • Pawlicki T

    1. Oregon State University, Corvallis, OR
    2. Washington University School of Medicine, Saint Louis, MO
    3. Washington University in St. Louis, St. Louis, MO
    4. Washington University, St. Louis, MO
    5. Washington University, St. Louis, MO
    6. Washington University School of Medicine, Saint Louis, MO
    7. UCSD Medical Center, La Jolla, CA
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Abstract

Purpose:

New techniques and materials have recently been developed to expedite the conventional Linac Acceptance Testing Procedure (ATP). The new ATP method uses the Electronic Portal Imaging Device (EPID) for data collection and is presented separately. This new procedure is meant to be more efficient then conventional methods. While not clinically implemented yet, a prospective risk assessment is warranted for any new techniques. The purpose of this work is to investigate the risks and establish the pros and cons between the conventional approach and the new ATP method.

Methods:

ATP tests that were modified and performed with the EPID were analyzed. Five domain experts (Medical Physicists) comprised the core analysis team. Ranking scales were adopted from previous publications related to TG 100. The number of failure pathways for each ATP test procedure were compared as well as the number of risk priority numbers (RPN's) greater than 100 were compared.

Results:

There were fewer failure pathways with the new ATP compared to the conventional, 262 and 556, respectively. There were fewer RPN's > 100 in the new ATP compared to the conventional, 41 and 115. Failure pathways and RPN's > 100 for individual ATP tests on average were 2 and 3.5 times higher in the conventional ATP compared to the new, respectively. The pixel sensitivity map of the EPID was identified as a key hazard to the new ATP procedure with an RPN of 288 for verifying beam parameters.

Conclusion:

The significant decrease in failure pathways and RPN's >100 for the new ATP mitigates the possibilities of a catastrophic error occurring. The Pixel Sensitivity Map determining the response and inherent characteristics of the EPID is crucial as all data and hence results are dependent on that process.

Grant from Varian Medical Systems Inc.

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