Date Approved

8-5-2025

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Health Professions

First Advisor

Sarah Johnson

Second Advisor

Kristen Vu

Academic Year

2024/2025

Abstract

Purpose This study aims to compare the dosimetric performance of 6 MV and 10 MV photon beam energies in stereotactic body radiation therapy (SBRT) for adrenal tumors. Given the anatomical complexity of the adrenal region and its proximity to critical organs, optimizing beam energy selection is essential to maximize tumor control while minimizing normal tissue toxicity. Methods and Materials A retrospective study analysis was conducted using treatment plans from ten patients with adrenal metastases. Each case was planned with volumetric modulated arc therapy (VMAT) using both 6 MV and 10 MV beam energies. Dosimetric metrics assessed included target coverage, conformity index (CI), homogeneity index (HI), gradient index (GI), and dose to organs at risk (OARs). Plans were evaluated using the Eclipse treatment planning system. Statistical comparisons were made using the sign test, with significance set at p < 0.05. Results Both energies achieved clinically acceptable PTV coverage with no significant differences in CI, HI, or D95%, D98%, and D100%. However, 6 MV plans demonstrated a significantly lower GI (mean 3.82, p = 0.0391), indicating a steeper dose fall-off. In contrast, 10 MV plans provided superior sparing of critical organs, with significantly reduced doses to the skin and the heart at 0.5 cc volumes (p = 0.0215). No significant differences were observed in MU efficiency or dose to other OARs. Conclusion Both 6 MV and 10 MV photon beams are dosimetrically suitable for adrenal SBRT. 6 MV offers sharper dose gradients, making it preferable when a steep fall-off is needed near sensitive structures. Conversely, 10 MV provides better sparing of certain OARs, particularly the skin and heart. These findings support the selection of energy tailored to tumor location and proximity to critical organs, especially in settings without access to flattening filter-free (FFF) beams.

Download

Share

COinS