Date Approved

8-11-2021

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Health Professions

First Advisor

Dr. Kathryn Barnhart

Academic Year

2020/2021

Abstract

Abstract Introduction The purpose of the work is to see if there is a dosimetric benefit to using one treatment modality over another when treating centrally located brain tumors. These modalities include helical tomotherapy, non-coplanar VMAT, and coplanar VMAT. Methods Thirty plans were created from ten previously treated patient’s datasets. All patients were planned using a simultaneously integrated boost with a PTV54 and PTV 60. The conformity index and homogeneity index were compared for targets. Dose maximums and means were compared for critical structures between the plans and modalities. Results A significant difference was found for the conformity index for 5400 cGy where helical tomotherapy was the furthest from 1 by more than 10%. For 95% of the higher prescription dose of 6000cGy (5700cGy), the mean conformity index was significantly closer to 1 for helical tomotherapy by more than 20% compared to the other two modalities. Helical Tomotherapy had a significantly higher dose to both lenses and both optic nerves as well as a higher mean dose for the brain stem and normal brain subtracting the PTVs. Helical tomotherapy met all dose constraints for all plans where coplanar VMAT and non-coplanar VMAT did not for two patients where the brainstem was within 3mm of the PTV60. Conclusion For centrally located brain tumors, helical tomotherapy was able to meet all constraints and had a higher CI for 95% of higher target volume. Non-coplanar and coplanar VMAT’s dose to normal structures were comparable and lower than helical tomotherapy but were unable to 3 meet brain stem dose constraints for 2 patients. While all modalities have proven acceptable and useful in treating centrally located brain tumors, the author recommends using HT.

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