Date Approved

8-8-2022

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Health Professions

First Advisor

Sarah Johnson

Academic Year

2021/2022

Abstract

Introduction

Prevalence of early-stage breast cancer is increasing with the aid of preventative screenings and early diagnosis. The standard of care is transforming from conventional approaches with long treatment regimens towards hypofractionation and tissue sparing techniques. Based on studies over the past ten years, there are reasons to consider a partial-breast, hypo fractionated treatment option in the supine position. In practice, aPBI is often produced using several static intensity modulated beams to control dose to the normal breast tissue and limit dose to the heart and lungs. Patients may also be treated in the prone treatment setup in order to maximize the potential for tissue and organ sparing. These techniques: accelerated partial breast irradiation and prone treatment planning, combined, can conclude whether patients with early-stage breast cancer can benefit from furthering research and treatment planning in this modality.

Methods

This study gathers ten patients and uses their anonymized data scans to formulate a retrospective analysis comparing static IMRT and IMRT VMAT plans for evaluating dose to the heart, lungs, contralateral breast and affected breast tissue. Planning target volumes that coincide with the aPBI recommendations for treatment are created based on the tumor bed. Beam arrangements and plans are created with ALARA in mind and dose constraints based on a phase III study called the Florence Trial.

Results

Results were analyzed from SPSS data outputs and Wilcox sign rank tests. Tests ran show statistically significant lower dose to heart, lungs, and contralateral breast in the Static IMRT treatment plans compared to the VMAT IMRT plans.

Conclusion

The current method of using static IMRT fields has the lowest overall dose to the heart, lungs, contralateral breast, and normal breast tissue due to the ability to control the entrance and exit dose. The VMAT plans produced acceptable homogenous dose to the PTV but were statistically higher in dose due to the inability to prevent exit dose in critical organs at risk. This is partially due to the minimum arc length limitations, the need to cover the PTV and control high dose, clearance limitations for beam angles, and patient anatomy. Static IMRT beam arrangements would be beneficial for treating patients in the prone position.

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