Date Approved


Graduate Degree Type


Degree Name

Medical Dosimetry (M.S.)

Degree Program

Health Professions

First Advisor

Kristen Vu

Second Advisor

Dr. Kathryn Barnhart

Academic Year




As age increases, so does the chance of developing prostate cancer. The key to a successful outcome is early screening and diagnosis. Treatment options for prostate cancer include observation, surgery, radiation therapy, and/or hormonal therapy depending on the stage of disease. The purpose of this study was to analyze the dosimetric impact of using 4DOF versus 6DOF when aligning patients for treatment, specifically focusing on metrics including the PTV V95, PTV V105, Max Bladder dose, rectum V50, and femoral heads V20.


Eight patients with intermediate to high-risk prostate cancer treated in 2018-2019 from a Midwestern Hospital were selected to participate in this retrospective, quantitative study. The patients were treated with a Varian Linear Accelerator equipped with a Varian Medical System Perfect Pitch™ Couch and VMAT, IGRT, and CBCT capabilities. All patients included in the study were treated with a VMAT technique with two full arcs.


Key findings reveal PTV V105% was highest in the 4DOF ProstBST plan and lowest in the 4DOF ProstSV plan. PTV V95% was similar among all plans. Median OAR doses for each plan were also almost equal, with the greatest difference being in the bladder maximum value. The maximum bladder dose was higher in the 4DOF plan than the 6DOF plan. The V20 for the Left femoral head was higher in the 4DOF plan and the right femoral head V20 was higher in the 6DOF plan. The rectum V50 was also higher in the 6DOF plan. According to the results, the 6DOF plan had greater coverage for PTV1 than the 4DOF plan, while the coverage for PTV2 was higher in the 6DOF plan.


Results indicated that utilizing all 6 DOF does not have a statistically significant impact on the coverage of the target volume or dose to critical structures. Future studies with larger sample sizes are necessary to gain a better prospective of findings with more data.