Date Approved

9-27-2021

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Allied Health Sciences

First Advisor

Lauren Rydquist

Second Advisor

Kristen Vu

Academic Year

2020/2021

Abstract

Introduction

VMAT planning techniques have been used more to treat difficult‐to‐plan post‐mastectomy cases. The primary advantage of VMAT is the better performance at intermediate-high dose sparing and mean heart dose, without sacrificing target coverage. The location of the chest wall leads to clinical target volumes (CTV) adjoined to the skin which would generate a planning target volume (PTV) located outside the body. To overcome these limitations a virtual bolus is used during optimization. The purpose of the study is to evaluate if a VMAT technique without a bolus, with 5 mm virtual bolus, or 1 cm virtual bolus provides better conformity and homogeneity while delivering adequate dose to the skin of the chest wall.

Methods

Three VMAT plans were created for ten female left sided breast cancer patients post-mastectomy treatments. A virtual bolus was created in various thickness of 5 mm and 1 cm for the optimization phase only. The plans were labeled NB- no bolus, 5 mm- 5 mm bolus and 1 cm- 1 cm bolus. In total thirty plans were created for the study.

Results

The main effect of bolus on CI and HI was not significant. CI: WL= .984, F (2, 8) = .066, p = .94; HI: WL = .567, F (2, 8) = 3.06, p = .10. The results showed that there was no significant effect of bolus on skin V5 or skin V85. Skin V5, WL = .668, F (2,8) = 1.99, p = .199; skin V85, F (1.06, 9.5) = .256, p = .638.

Conclusion

The results were not statistically significant in the metrics of conformity, homogeneity, and dose to the skin of the chest wall. The 1 cm bolus plans did have higher means in conformity, homogeneity, and skin V5.

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