Date Approved

8-6-2024

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Allied Health Sciences

First Advisor

Mubin Shaikh

Second Advisor

Kristen Vu

Academic Year

2023/2024

Abstract

Abstract

Introduction

Soft tissue sarcomas (STS) affect about 13,500 people annually in the United States, and those in the lower extremities present unique challenges in radiation therapy due to the wide variability in tumor sizes, sometimes exceeding 30cm. Traditional treatment involves C-Arm linear accelerators using Volumetric Modulated Radiation Therapy (VMAT), which provides precise targeting while sparing nearby organs. Helical Tomotherapy (HT) is another option, delivering radiation in a helical pattern with a binary MLC for a uniform dose distribution. However, no studies have compared VMAT and HT for lower extremity sarcomas of different sizes. This study aims to compare these modalities to identify superior planning metrics for various tumor sizes.

Methods

We retrospective analyzed 12 patients with lower extremity sarcomas, categorized by tumor size: small (<10cm), medium (>10cm but <15cm), and large (>15cm). HT plans were created using Accuray Precision, while VMAT plans were generated with Pinnacle 3, adhering to ASTRO guidelines. Metrics assessed included Conformity Index (CI), Homogeneity Index (HI), mean skin strip dose, and Monitor Unit (MU) Factor.

Results

Results showed HT achieved a better HI (mean 1.070) compared to VMAT (mean 1.090, p=0.020), indicating more uniform dose distribution. However, VMAT had a superior CI (mean 0.988) compared to HT (mean 1.050) for small and medium tumors (p<0.001). HT also resulted in higher mean skin strip doses (944.25cGy vs. 616.71cGy for VMAT, p=0.002) due to its delivery pattern.

Conclusion

In conclusion, HT offers better dose homogeneity, while VMAT excels in conformity, particularly for smaller tumors. This study aids clinicians in optimizing treatment plans based on tumor characteristics, balancing treatment efficacy with practical considerations like skin dose and treatment time.

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