Date Approved

8-10-2026

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

School of Interdisciplinary Health

First Advisor

Kristen Vu

Second Advisor

Sarah Johnson

Academic Year

2025/2026

Abstract

Purpose: To evaluate whether implementing a staggered beam arrangement in volumetric modulated arc therapy (VMAT) improves treatment plan quality by enhancing normal tissue and organ-at-risk (OAR) sparing in patients with localized prostate cancer.

Methods: Ten patients meeting the study inclusion criteria were retrospectively replanned using both a standard arc technique and a staggered arc arrangement. Both plans were generated using identical optimization objectives and planning parameters. Dosimetric comparisons were performed after normalizing both plans to equivalent planning target volume (PTV) coverage. Dose-volume metrics were evaluated for the PTV, rectum, bladder, and penile bulb.

Results: The staggered beam arrangement produced statistically significant improvements in selected OAR dosimetric parameters. The greatest reductions were observed in select rectal and penile bulb dose metrics, whereas bladder dose-volume parameters remained unchanged. Although statistically significant, the magnitude of the dosimetric improvements was modest.

Conclusion: A staggered VMAT beam arrangement resulted in modest improvements in selected rectal and penile bulb dosimetric parameters while maintaining equivalent PTV coverage. Although these differences reached statistical significance, their clinical relevance remains uncertain. Further investigation with larger patient cohorts and additional treatment sites is warranted to determine the clinical significance and broader applicability of this planning approach.

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