Date Approved

8-5-2024

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Health Professions

First Advisor

Kristen Vu

Second Advisor

Jeannie Anderson

Third Advisor

Alex Zaharakis

Academic Year

2023/2024

Abstract

Introduction

This research was conducted for carcinoma of the left breast without nodal involvement using the 3D deep inspiration breath hold (DIBH) treatment technique. Limiting dose to healthy tissues is crucial in radiation treatment planning. The impact of dosimetric uncertainty due to isotropic variations on constraints and goals is often overlooked. This study investigates dose metric differences due to inherent patient misalignment modeled by isotropic variations in treatment planning.

Methods

10 patient subjects were randomly selected with carcinoma of the left breast without nodal involvement, each using the 3D hypofractionated, deep inspiration breath hold (DIBH) technique. All plans had 24 different plan iterations created using the uncertainty analysis tool in the Eclipse treatment planning system (TPS). Nine dose constraints were evaluated in which data was collected and statistically analyzed based on metrics such as standard deviation, mean, percentage differences and absolute deviation.

Results

Based on the analyzed data, most metrics ended with a passing result based on department standards for goals and constraints, regardless of the shift magnitude. Larger shift magnitudes created larger percentage differences, specifically in the posterior and right directions, especially in terms of ipsilateral lung and heart constraints.

Conclusion

Uncertainty in treatment planning is unavoidable. When considering setup uncertainties, there is a directional dependence on planning goal failures. This warrants a departmental discussion and further research, during planning and daily setup, when using a surface guided technique or daily imaging.

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