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Establishing Institution-Specific Action Levels for EPID-Based QA for IMRT

A Gray

A Gray*, A Saldan, D Rosenzweig, R Meiler, D Clark, R Abu-Aita, M Schell, D Cavanaugh, The University of Rochester Cancer Cen, Rochester, NY

SU-E-T-207 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To establish institutionally specific action levels for quality assurance (QA) of
intensity-modulated radiation therapy (IMRT) treatment plans based on the guidelines and
statistical principles presented by Howell et al. in 2008 for the University of Texas MD

Methods: A review of 3937 fields of 364 patients treatment plans was undertaken to find
institutional action level values unique to this clinic. Data analysis focused on the commonly
used gamma parameter. Institutional averages and standard deviations were found for
maximum gamma, average gamma, and percentage of a field's fluence area exhibiting a gamma
value greater than 1.0. Additional analysis reviewed action level dependence on disease site and EPID acquisition software version.

Results: These observations were used to create action levels specific to this clinic and which were found to be substantially stricter than those recorded by Howell et al; this difference perhaps reflects institution-specific aspects such as updated acquisition software and individual treatment planning styles.

Conclusion: Results suggest that action levels for Portal Dosimetry-based IMRT QA should be
adjusted based on individual institutional experience.

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