Date Approved


Graduate Degree Type


Degree Name

Medical Dosimetry (M.S.)

Degree Program

Diagnostic & Treatment Sciences

First Advisor

Kristen Vu

Academic Year



Utilization of a bellyboard device reduces small bowel dose for patients receiving radiation therapy for rectal cancer. The reduction of small bowel dose with the bellyboard is even more significant in intensity modulated radiation therapy rectal treatments, as opposed to conventional 3D treatments. However, there is evidence of increased setup variation with prone bellyboard positioning, especially in pitch and roll. The purpose of this study is to determine the margin needed between the clinical target volume and the planning target volume to adequately account for these setup variations when planning volumetric modulated arc therapy rectal cases utilizing the bellyboard device. The most preferable margin will provide the highest clinical target volume (CTV) dose coverage without significantly increasing normal tissue dose, as assessed through on-treatment cone beam computed tomography imaging.