Date Approved

7-2020

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Diagnostic & Treatment Sciences

First Advisor

Kristen Vu

Academic Year

2020/2021

Abstract

Introduction: Whole breast irradiation (WBI) for early stage left-sided breast cancer (BC) exposes critical structures to additional radiation and increases risk of long-term complications. Partial breast irradiation (PBI) treatments have been pursued to help reduce dose to critical structures, but some patients may not be good candidates for current PBI deliveries. Evaluating how robust optimization (RO) effects target coverage and dose to critical structures is critical in developing new methods of delivering PBI.

Methods: This retrospective study consisted of 10 randomly selected female patients with early stage left-side BC previously treated with 3-dimensioinal conformal radiotherapy (3D-CRT) WBI. Each patient had two new 5-field non-coplanar intensity modulated radiotherapy (IMRT) PBI plans created. One plan utilized RO, and the other plan was optimized without using RO. Target coverage, and dose to the lung, heart, and healthy breast tissue was measured and dosimetrically evaluated for each treatment planning technique.

Results: Results of the study indicated that the RO IMRT PBI plans delivered a statistically significant lower dose to the target compared to the 3D-CRT WBI and non-RO IMRT PBI plans; however, RO IMRT was able to significantly limit dose to critical structures compared to 3D-CRT WBI.

Conclusion: Using RO for IMRT PBI may provide adequate target coverage while limiting dose to critical structures for patients that are not good candidates for other PBI delivery methods. Having a 10-phase 4DCT that tracks the respiratory cycle for treatment planning opposed to a 3DCT may provide additional information to determine how RO truly effects prescription dose to the target.

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