Date Approved

8-11-2026

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Allied Health Sciences

First Advisor

Dr. Shaikh Mubin

Second Advisor

Kriten Vu

Academic Year

2025/2026

Abstract

Abstract

Purpose: To compare dosimetric outcomes between volumetric modulated arc therapy (VMAT)-only and hybrid VMAT plus three-dimensional conformal radiotherapy (3D-CRT) techniques for accelerated partial breast irradiation (APBI) in patients with early-stage left-sided breast cancer.

Methods and Materials: Thirty patients treated with APBI at a single institution were retrospectively replanned using both VMAT-only and hybrid (VMAT + 3D-CRT) techniques. All plans were prescribed 26 Gy in 5 fractions. Each patient was planned using the same target volumes, optimization objectives, and evaluation criteria for both techniques. Planning target volume (PTV) coverage, conformity index (CI), homogeneity index (HI), hotspot control, organ-at-risk (OAR) doses, and monitor units (MU) were compared. Statistical analyses were performed using paired Student's t-tests or Sign tests, as appropriate, with p < 0.05 considered statistically significant.

Results: Both techniques achieved excellent target coverage. Mean PTV_eval V95 % was 99.13 % ± 2.95 for VMAT and 99.20 % ± 2.78 for hybrid plans. The hybrid technique demonstrated significantly improved hotspot control, with lower V105 % (0.17 % ± 0.28 vs. 1.53 % ± 1.96, p = 0.0003) and improved dose homogeneity. Hybrid plans significantly reduced mean heart dose (.95 Gy vs. 1.17 Gy, P < 0.0001), heart V15 %, ipsilateral lung V10 %, contralateral lung V5 %, and contralateral breast mean dose. Hybrid plans also required fewer monitor units (976 vs. 1319.97, P < 0.0001). VMAT provided improved sparing of the ipsilateral breast, with lower V50 % and V95 % values.

Conclusions: Hybrid APBI planning maintained target coverage while reducing monitor units and dose to the heart, lungs, and contralateral breast. Hybrid planning may be a valuable alternative for selected patients when minimizing dose to surrounding normal tissues is a priority.

Download

Share

COinS