Date Approved

8-12-2026

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

School of Interdisciplinary Health

First Advisor

Addah Riebschleger

Second Advisor

Kristen Vu

Academic Year

2025/2026

Abstract

Purpose:

To evaluate the dosimetric performance and delivery efficiency of 6MV flattening filter free (6FFF) and 10MV flattening filter free (10FFF) VMAT beam energies for deep inspiration breath- hold (DIBH) liver stereotactic body radiation therapy (SBRT), with emphasis on treatment time, breath-hold demands, and organ at risk (OAR) sparing.

Methods:

Ten previously treated DIBH liver SBRT patients were retrospectively replanned using standardized VMAT geometry, identical optimization objectives, and consistent contouring. Each patient received paired 6FFF and 10FFF plans generated in Eclipse using AcurosXB. Dosimetric endpoints included target coverage, conformity index (CI), gradient index (GI), and OAR dose metrics based on institutional and RTOG guidelines. Efficiency metrics included monitor units (MUs), beam‑on time, and estimated breath‑hold cycles. Paired Wilcoxon signed‑rank testing was used to assess statistical significance.

Results:

Both beam energies achieved all target coverage goals, with no significant differences in CI or GI, indicating comparable conformity and dose falloff. OAR doses were largely equivalent between techniques, though 10FFF produced significantly lower kidney mean dose (P = .031) and stomach/duodenum maximum dose (p= .031). Treatment efficiency strongly favored 10FFF, reducing average MUs by ~290 and decreasing mean beam‑on time from 115.3 s (6FFF) to 60.3 s (10FFF), a 47.7% reduction. Shorter beam‑on times translated to fewer breath‑hold cycles and improved delivery reproducibility.

Conclusions:

10FFF VMAT provides equivalent dosimetric quality to 6FFF while substantially improving treatment efficiency for DIBH liver SBRT. The marked reduction in beam‑on time may enhance patient comfort, breath‑hold stability, and overall treatment safety. These findings support the preferential use of 10FFF for DIBH liver SBRT when clinically appropriate.

Download

Share

COinS