Date Approved

4-28-2026

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Health Professions

First Advisor

Bethany Marshall

Academic Year

2025/2026

Abstract

Abstract

Purpose

The purpose of this study is to determine the dosimetric impact on rectal dose by comparing two arc versus three arc VMAT plans on prostate patients who have received SpaceOAR.

 

Methods

A retrospective planning technique was performed on eight prostate cancer patients who had been previously treated with three-arc VMAT plans. For each plan, a two-arc plan was generated by removing the third arc and re-optimizing the plans using identical constraints and objectives. Dosimetric parameters were analyzed using dose volume histogram (DVH) analysis, including rectal dose metrics, V60 Gy, V65 Gy, V70 Gy, target coverage, PTV V95%, conformity index (CI), maximum dose (Dmax), and PTV minimum dose (PTV_Min).

Results

According to the comparative analysis conducted between the two planning techniques, the results demonstrated no statistically significant difference between the two-arc and three-arc plans. There were, however, improvements in the CI, 100% isodose volume, Dmax, and PTV minimum dose with the three-arc technique. Despite these differences, the magnitude of change in some of these parameters were relatively small, indicating that there was no clinical significance.

Conclusion

While the three-arc plans provided the best dose conformity and PTV coverage, it did not result in significantly reduced rectal dose, suggesting that two-arc plans may be more efficient without compromising clinical outcomes.

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