Date Approved

7-23-2025

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Health Professions

First Advisor

Brian Loughery

Second Advisor

Kristen Vu

Academic Year

2024/2025

Abstract

Abstract

Introduction: Accelerated partial breast irradiation (APBI) has emerged as a targeted alternative to whole-breast irradiation for early-stage breast cancer, particularly for patients with medially located, left-sided tumors. Static intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) offer advanced dose conformity, yet no direct comparisons between static IMRT and VMAT have been conducted specifically for medially located, left-sided APBI, a uniquely challenging anatomical subgroup. This study evaluates dosimetric differences between static IMRT and VMAT plans to determine which modality provides superior target coverage and organ-at-risk (OAR) sparing in left-sided APBI.

Methods: Ten patients with medially located left-sided breast cancer were selected for retrospective analysis. Each patient had static IMRT and VMAT plans generated using consistent target volumes and dose constraints aligned with APBI guidelines. Beam arrangements were selected to minimize dose to nearby organs while maintaining full coverage of the tumor bed. Dosimetric evaluation focused on target coverage, conformity, and dose to the heart, lungs, and contralateral breast. All comparisons were analyzed using the sign test.

Results: VMAT plans showed statistically significant improvements in target coverage, dose conformity, and lung sparing compared to static IMRT. No statistically significant differences were observed in heart dose or contralateral breast dose, though trends favored VMAT across these metrics.

Conclusion: VMAT provides significantly improved target coverage, superior moderate-dose conformity, and reduced low-dose lung exposure compared to static IMRT in medially located, left-sided APBI, while heart dose differences remain directionally favorable. These findings support VMAT as the preferred planning technique in anatomically challenging APBI cases, warranting further validation in larger cohorts.

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