Semester of Graduation

Summer 2024

Degree

Master of Science (MS)

Department

Physics & Astronomy

Document Type

Thesis

Abstract

Radiotherapy is a common form of cancer treatment with approximately two thirds of patients receiving some form of radiation as part of their care. The increasing complexity of modern radiotherapy treatments has necessitated the practice of patient specific quality assurance (PSQA). PSQA typically is performed prior to a patient’s first treatment and consists of delivering the radiotherapy treatment to a device containing dosimeters. These measurements are compared with calculation using gamma index analysis to ensure the machine is capable of delivering an accurate treatment. However, measurement and calculation never agree perfectly, and it is difficult to estimate how small discrepancies as measured by PSQA devices will translate to the patient’s actual treatment. This has led to interest in log-file based PSQA in which records of the machine state during treatment delivery are used to reconstruct the dose to the patient. This work’s purpose is to compare log-file based PSQA methods to standard measurement based PSQA at a radiotherapy clinic. A group of clinical prostate and head-and-neck treatment plans were anonymized for this work. In specific aim 1, the reproducibility of log-file based PSQA methods is compared to measurement over repeated deliveries on a single machine as well as deliveries on two matched treatment machines. In specific aim 2, the sensitivity of PSQA to simulated treatment delivery errors is compared with measurement by intentionally modifying certain delivery parameters and comparing the results of each PSQA method. In specific aim 3, a variation of log-file based PSQA that compares changes between planned and log-file reconstructed patient dose volume histograms (DVHs) as an alternative to gamma index analysis is tested. The in-house log-file PSQA method performed similarly to the standard measurement based method. All unmodified plans passed both PSQA methods, and variations in the results of x each method across multiple deliveries and multiple machines were also similar. Standard PSQA was more sensitive to simulated errors than log-file PSQA based on gamma index analysis, but log-file PSQA based on DVH metrics was most sensitive, but also resulted in some unmodified plans failing. This work suggests log-file PSQA is a viable alternative to measurement.

Date

5-28-2024

Committee Chair

Christopher Schneider

DOI

https://doi.org/10.31390/gradschool_theses.5991

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Available for download on Friday, May 16, 2031

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