Date Approved

7-20-2021

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Health Professions

First Advisor

Dr. Heather Wallace

Academic Year

2020/2021

Abstract

Introduction

Total body irradiation (TBI) plays a critical role in the myeloablative conditioning regimen for stem cell transplantations due to its ability to deliver dose to all tissues including sanctuary sites, giving an opportunity for cure in children suffering a relapse of leukemia. VMAT-TBI techniques have become the standard practice, but toxic doses to organs at risk (OARs) can lead to long-term complications, particularly in children who are living longer as cure rates improve. The purpose of this study is to demonstrate the feasibility of a simultaneous integrated boost (SIB) TBI technique to deliver a sufficient dose to the marrow, while reducing doses to sensitive OARs.

Methods

In this retrospective study, five pediatric patients who were previously treated with the institution’s traditional VMAT-TBI technique were replanned using an SIB-TBI approach. The planning aims for the conventional TBI were designed to deliver 12 Gy in six fractions to a minimum of 90% of the total body. Planning aims for the SIB-TBI technique were to deliver 12 Gy to at least 90% of the marrow and 8 Gy to at least 90% of the total body while limiting the mean lung dose to less than 8 Gy.

Results

All five patients had significant reductions in mean dose to the lungs, heart, kidneys, and bowel, while achieving 12 Gy to at least 90% of the marrow and 8 Gy to at least 90% of the total body. Additionally, coverage of sanctuary sites in the central nervous system was maintained and maximum doses less than 16 Gy (130%) were achieved in the SIB-TBI plans.

Conclusion

This study supports the feasibility of SIB-TBI technique as an alternative to the institution’s conventional VMAT-TBI regimen. SIB-TBI provided adequate doses to the marrow and sanctuary sites, while delivering reduced doses to the OARs. Future research should evaluate the radiobiological effects to OARs with the reduction in dose associated with the use of an SIB-TBI technique.

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