Date Approved

6-25-2026

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

School of Interdisciplinary Health

First Advisor

Xuanfeng Ding

Second Advisor

Kristen Vu

Third Advisor

Xiaoda Cong

Fourth Advisor

Congxiao Chen

Academic Year

2025/2026

Abstract

Head and neck cancer patients often experience anatomical changes during radiation therapy, including weight loss and tumor regression. These changes can alter planned dose distribution and affect treatment accuracy. Based on the previous understanding, IMPT offers highly conformal dose delivery but is sensitive to the patient’s geometry changes and daily setup uncertainties, while VMAT may provide greater stability under these uncertainties. However, as of today, there is no quantitative analysis and comparison between the two modalities using real clinical data. The purpose of this study is to compare the robustness of IMPT and VMAT for head and neck cancer by evaluating target coverage and OAR sparing during the entire treatment course. This is a retrospective paired planning study that includes ten head and neck cancer patients previously treated with IMPT. A comparative VMAT plan was generated for each patient using the original planning CT scans. Fractional doses were accumulated over the treatment course. DVH analysis evaluated dose to 98% CTV coverage (D98), and the volume receiving 100% of the prescription dose (V100). Each OAR was accessed and compared in the doses they received, using a paired t test. Both modalities maintained comparable D98 target coverage after dose accumulation. However, VMAT demonstrated greater robustness in preserving V100 coverage throughout treatment. IMPT showed greater sensitivity to anatomical change, with larger dose variation in several OARs. Differences between IMPT and VMAT were higher for the oral cavity (Δ mean 0.15), spinal canal at 5000 cGy (Δ mean 0.50), left optic nerve (Δ mean 1.10), and right optic nerve (Δ mean 0.42). Significant differences favoring VMAT stability were observed for the oral cavity (P = .0371) and left optic nerve (P =.0488). Although IMPT provided strong initial conformality and reduced integral dose, it was more sensitive to anatomical change. VMAT demonstrated greater robustness in maintaining V100 target coverage. These findings support consideration of adaptive replanning, particularly for proton-treated head and neck cancer patients. Additionally, findings show that both modalities have beneficial effects for head and neck cancer patients.

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