Access Type

Open Access Dissertation

Date of Award

January 2024

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Medical Physics

First Advisor

Michael Snyder

Abstract

Radiotherapy plays an essential role in post-operative management of breast cancer. Unfortunately, the doses required to eradicate malignant tissue also cause radiation-induced skin damage. The more severe effects often require treatment postponement or cessation, which can impact the probability of local control and lasting negative effects.Acute skin reactions are subjectively evaluated by the clinician according to NCI’s CTC or RTOG scoring systems. The criteria for acute radiation morbidity ranges from grade 1 to 4 for adverse advents. The onset of symptoms typically occurs approximately two weeks into treatment and is dose dependent. Given radiation-induced skin injury remains a dose limiting complication, a means to detect skin changes prior to clinical manifestation for potential treatment adaptation is needed. If one could relate skin toxicity to a measurable quantity, the clinician could prophylactically adapt any number of parameters from the treatment to help reduce the patient’s risk. Utilizing microcirculation as a surrogate for this radiation skin response would provide quantitative metrics for the prediction of acute skin toxicity prior to clinical manifestation. We aim to identify an optical imaging technique to assess changes in microcirculation and identify patients at risk for impending skin reactions. As the blood flow changes are non-visible, signal post-processing methods are required to magnify these changes for visualization and quantification. Overall, the methods developed were able to use a simple digital camera to acquire videos of 10 second or less duration to capture cardiac signals. Accurate determination of a single heart rate was plausible in humans and limited to a broader range in mice. The Eulerian video magnification technique was built into a framework to amplify pixel values corresponding with extracted heart rates to depict nonvisible signals. The extracted heart rate was also utilized to determine the amplitude of this signal in the frequency-domain and plotted onto a two-dimensional pulse map. Various pre-clinical studies were utilized to fine tune workflows for these techniques. Ultimately, a breast radiotherapy clinical trial found agreement between EVM amplitude and pulse mapping with thermal imaging temperature results prior to the clinician noticing any toxicity, indicating their potential to predict impending reactions. Overall, both the EVM and pulse mapping techniques show promise as a means to diagnose skin reactions in breast radiotherapy prior to clinical manifestation.

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