Date Approved

8-7-2023

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Health Professions

First Advisor

Bethany Marshall

Academic Year

2022/2023

Abstract

Introduction

Breast cancer is a prevalent disease in the United States, affecting approximately one in eight women during their lifetime (Leaver & Washington, 2010). Advancements in medical treatments have evolved from mastectomy to a multidisciplinary approach. Radiation therapy plays a crucial role in preventing local recurrence after breast conserving surgery. Traditionally, whole breast irradiation has been administered over 25-28 fractions to a total dose of 45-50 Gray (Gy), followed by a boost of 5-8 fractions to the tumor bed. In recent times, hypofractionation, which involves a shorter treatment schedule of 15-16 fractions to a total dose of 42.5 Gy, followed by a boost of 10 Gy in 5 fractions, has emerged as a standard for whole breast irradiation. Hypofractionation offers shorter treatment schedules without compromising outcomes.

Materials and Methods

This retrospective study aimed to assess the dosimetric benefits of reducing the inferior border from 2 centimeters(cm) to 1.5cm in tangential right-sided intact breast radiation plans receiving hypofractionated treatment schedules. The primary objective was to evaluate the liver volume receiving 30Gy and the maximum liver dose comparatively between the two treatment plans. Twenty-five female patients who underwent a lumpectomy and received a hypofractionated treatment prescription with free breathing were included. Additional parameters of coverage, V16Gy (%) and V8Gy (%) of the right lung, were also evaluated.

Results

Results showed that reducing the inferior border to 1.5cm led to decreased dose to the liver and right lung, indicating potential benefits in terms of reducing radiation-induced side effects. However, there was a minor decrease in coverage when compared to the standard 2cm border plans. Outliers were observed in large livers, necessitating further studies to evaluate a patient's liver size and weight as potential risk factors for liver side effects.

Conclusion

Further research with a larger patient population is needed to validate these findings and explore potential risk factors for right-sided free breathing breast irradiation receiving a hypofractionated schedule. This study also highlights the importance of radiation oncologists' careful planning to minimize exposure to organs at risk (OAR) while maintaining adequate coverage and accounting for set-up accuracy and reproducibility.

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