Date Approved

7-8-2021

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Health Professions

First Advisor

Kristen Vu

Academic Year

2020/2021

Abstract

Abstract

Introduction

The purpose of the present work was to determine if the use of biological-based objectives on target volumes and critical structures in the optimizer could produce a superior plan when compared to using only physical objectives for patients with intermediate-risk prostate cancer with insertion of SpaceOAR Hydrogel.

Methods

Three planning techniques were created and compared retrospectively for 10 different radiation therapy patients using Varian Eclipse treatment planning system utilizing volumetric modulated arc therapy (VMAT) treatment planning. Each technique used different planning objectives including dose volume (DV) objectives, target generalized equivalent uniform dose (gEUD) objectives, and a combination of DV objectives with target and critical structure gEUDs. Doses to target volumes and organs at risk were analyzed using dose volume histograms and dose statistics for each plan.

Results

Based on dose volume histograms and dose statistics it was determined the utilization of biological-based objectives produced improvements to plan quality. The target gEUD allowed for decreased maximum dose and better fall off to the targets receiving 103% of the dose. The target gEUD reported more conformal and homogeneous treatment plans. The addition of upper gEUD objectives on the bladder and rectum resulted in significant improvements with reduction in dose mainly to the volumes receiving 80 Gy or more.

Conclusion

For the cases in this study, the addition of biological-based objectives resulted in improved maximum doses and critical structure dose sparing that is on par with, and mostly significantly lower than physical-based planning objectives. Recommendations were provided for alpha values and priorities for gEUD values on target volumes and critical structures.

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