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An Analysis of 13,000 Patient-Specific IMRT QA Results From 13 Different Clinical Treatment Services

K Pulliam

K Pulliam1*, D Followill1, L Court1, L Dong2, M Gillin1, K Prado3, S Kry1, (1)UT MD Anderson Cancer Center, HOUSTON, TX, (2) Scripps Proton Therapy Center, SAN DIEGO, CA, (3) University of Maryland, Baltimore, MD

MO-D-BRB-5 Monday 2:00:00 PM - 3:50:00 PM Room: Ballroom B

Purpose: To review an institution's patient-specific IMRT quality assurance (QA) results, including absolute dose and gamma analysis measurements.

Methods: Patient-specific IMRT QA records were reviewed to obtain information on absolute dose difference (ion chamber measurement; ±3% agreement criteria) and percentage of pixels passing gamma (film measurement; 5%/3 mm agreement criteria) from 2005 to 2011. The 13,002 plans reviewed, were classified by treatment service: breast (n=67), central nervous system (n=1383), gastrointestinal (n=803), genitourinary (n=1831), gynecology (n=935), hematology (n=380), head and neck (n=3697), intensity-modulated stereotactic spine radiation therapy (n=341), melanoma (n=54), mesothelioma (n=52), pediatric (n=307), sarcoma (n=201), and thoracic (n=2951). All records were analyzed for trends according to measurement date and treatment service. Plans failing to meet QA criteria were further evaluated for subsequent measured data.

Results: Mean difference (± one standard deviation) between the measured and calculated doses was -0.29% ± 1.64% (with the calculated values being slightly higher). The mean percentage of pixels passing gamma was 97.7% (lower 95th percentile, 92.2%). The plan pass rates were 97.7% and 99.3% for absolute dose and gamma, respectively. We observed statistically significant differences (p < 0.05) in both absolute dose and gamma measurements as a function of treatment service (particularly for stereotactic spine and mesothelioma services) and measurement date (average agreement improved with time). However, despite improved agreement between measured and calculated doses, the percentage of treatment plans failing to meet the passing criteria has remained largely constant at ~2.3%.

Conclusions: Our retrospective review of 13,002 patient-specific IMRT QA plans demonstrated that plans continue to fail IMRT QA criteria at a consistent rate. This rate serves as a clinical reference for expected rates of QA plan pass and failure for a variety of treatment services.

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