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Doctor of Philosophy (PhD)
Dr. Wei Luo
The technological advancements in brachytherapy have allowed for increased precision and better-quality treatments. This is apparent in treating GYN cancers of the uterine cervix. Lengthy low dose rate (LDR) treatments, implant systems, and two-dimensional (2D) image-guided treatments have been replaced by quicker high dose rate (HDR) treatments and adaptive treatment planning with three-dimensional (3D) imaging modalities. However, this increased precision can result in reduced dosimetric accuracy. Implant systems were designed to conform to the prescribed dose, and 2D plans were only concerned with dose to two organs at risk (OAR) parameters. Now, planners must consider added OAR position data and multiple OAR dosimetric parameters when planning adaptive 3D HDR cervical cancer brachytherapy treatment plans. This results in interfraction dose variations, and dose variations (DV) from the prescribed dose.
The purpose of this dissertation is the investigation of the dosimetric and clinical effects of DVs from the prescribed dose. DVs are uncertainties in the context of brachytherapy. The reduction of uncertainties for patient treatments is the goal of any physicist. And the first step to reducing uncertainties is to identify and quantify them. DV uncertainty was quantified using statistical models to identify trends in the DV data and to determine the effect on OARs. This DV uncertainty quantification established the DV portion of the cervical cancer brachytherapy uncertainty budget. The known DV uncertainty from the statistical models was used to hypothesize the clinical effect of DV uncertainty on clinical outcomes via Monte Carlo simulations of patient treatments. Lastly, the actual clinical outcomes were evaluated under the influence of DV uncertainty to determine the clinical effect of DV uncertainty.
In this dissertation, we have found that DV uncertainty results in tumor coverage loss and affects clinical outcomes. There is a 32.5% probability of under-dosing the high-risk clinical target volume (HRCTV), 1% of local control is loss for every -5% DV uncertainty, and 1% of pelvic control is loss for every -1.4% DV uncertainty. This effect is more profound for larger tumors. DV uncertainty reduces the local control probability by as much as 2.68% for large HRCTVs, DV uncertainty increases the treatment failure rate by as much as 1.7% (24σ) for large HRCTVs, and 1% of local control is loss for every 7.23 𝑐𝑐𝑚𝑚3 increase in HRCTV size. From the results of this dissertation, DV uncertainty has a profound effect on HDR brachytherapy for cervical cancer. DV uncertainty must be mitigated in clinic to improve treatment quality and clinical outcomes.
Lyman T. Johnson Fellowship (2019-2021)
University of Kentucky Department of Radiation Oncology (2019-2023)
Washington, Brien, "DOSIMETRIC AND CLINICAL INVESTIGATION INTO DOSE VARIATIONS OF THE TARGET AND ORGANS AT RISK IN HIGH DOSE RATE GYNECOLOGICAL BRACHYTHERAPY" (2023). Theses and Dissertations--Radiation Medicine. 6.
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