Date Approved

7-28-2025

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Allied Health Sciences

First Advisor

Tasha Potts, MS., CMD, RT(T)

Second Advisor

Kristen Vu, M.S., CMD, RT(T)

Academic Year

2024/2025

Abstract

This study evaluated the impact of Pinnacle³ version 18.0 auto-planning advanced settings modulation amount, monitor unit (MU) level, and dose fall-off priority on volumetric modulated arc therapy (VMAT) plan quality for bilateral oropharyngeal cancer. A total of 64 plans were generated using all possible combinations of low, medium, high, and very high settings for each parameter. A standardized base of tongue case was optimized once per plan using a single-time point approach, with planned target volume 1 (PTV1) (6996 cGy) and planned target volume 2 (PTV2) (5412 cGy) coverage evaluated. Each parotid gland, the spinal cord, brainstem, and the oral cavity dose metrics were evaluated. Two-way analyses of variance were performed to assess main effects and interactions for each setting on target coverage and organ at risk (OAR) sparing. Dose fall-off priority was the only factor that demonstrated a statistically significant main effect on both PTV1 (F3,60 = 1165.84; P <  .0001) and PTV2 (F3,60  = 2315.30; P <  .0001) coverage. Significant two-way interactions were also observed between dose fall-off priority and both modulation amount and MU level. For OARs, very high dose fall-off provided the most sparing to the brainstem and spinal cord, while low fall-off was optimal for parotid sparing. Seven unique setting combinations achieved both high PTV coverage and favorable OAR sparing. These results identify dose fall-off priority as the most influential planning parameter and suggest that balanced settings can improve plan quality and efficiency. Standardizing these advanced parameters may support more consistent, high-quality VMAT planning in clinical practice.

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