Date of Graduation


Document Type

Dissertation (PhD)

Program Affiliation

Medical Physics

Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

David S. Followill, PhD

Committee Member

Peter A. Balter, PhD

Committee Member

Laurence E. Court, PhD

Committee Member

Jennifer L. Johnson, MS, MBA

Committee Member

Stephen F. Kry, PhD

Committee Member

Francesco C. Stingo, PhD


Accurate delivery of intensity modulation radiation therapy (IMRT) requires perfect execution of a long, complicated chain of events; failure of any component of this process may contribute to dose delivery errors, compromising treatment quality and, more importantly, patient safety. Prospective, process-wide risk mitigation techniques are becoming more prevalent in radiotherapy to establish comprehensive quality management (QM) programs, such as failure modes and effects analysis (FMEA). The subjective nature of the ordinal scores used for FMEA leads questionable reliability and validity of the results. Additionally, physics components are commonly grouped together, leaving out valuable details important to physics QM. While the process of performing an FMEA is beneficial, it does not guarantee accurate assessment of failure modes. The objective of this project was to provide quantitative severity scores for IMRT delivery failure modes to decrease variability and increase the validity and applicability of FMEA results for improvement of physics QM. The hypothesis of this proposed work was that quantified IMRT physical failure mode severity scores were significantly more likely to describe the true severity compared to conventional qualitative scores. To test this hypothesis, physical failure modes were simulated in clinical IMRT patient treatment plans and the ability of qualitative subjective scores and quantitative scores to accurately describe the magnitude of the resultant dose discrepancies in clinical plans were compared. Qualitative subjective scores were obtained through an online survey of the medical physicist community. Quantitative scores were obtained through phantom treatment planning studies and measurements. Each set of severity data for the identified failure modes were compared to the true clinical severities in ten oropharyngeal patient treatment plans using Wilcoxon Signed Rank Tests. 8/11 failure mode true severity scores were predicted by quantitative approaches and 6/11 were predicted by qualitative approaches (p


FMEA, severity score, IMRT, IMRT errors, failure modes and effects analysis, quantitative severity score



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