Date Approved

8-3-2026

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

School of Interdisciplinary Health

First Advisor

Karen Chin Snyder, M.S., DABR

Second Advisor

Yimei Huang, PhD, DABR

Third Advisor

Kristen Vu, M.S., CMD, RT(T)

Academic Year

2025/2026

Abstract

Daily adaptive prostate stereotactic body radiation therapy (SBRT) is now feasible with advances in adaptive radiotherapy and automated optimization. However, the dosimetric quality of Ethos Intelligent Optimization Engine version 2 (IOE v2) automated plans may vary because optimization is based on user-defined templates rather than patient-specific dose guidance. This retrospective study evaluated whether integrating RapidPlan knowledge-based planning (KBP)–derived optimization objectives into the Ethos IOE v2 adaptive planning workflow improved dosimetric quality for prostate SBRT. Fifteen intact prostate SBRT patient datasets were evaluated. For each patient, three plans were generated: a baseline Ethos IOE v2 reference plan (Ref), a plan incorporating the initial RapidPlan model (RP1), and a plan incorporating the refined second RapidPlan model iteration (RP2). All plans used identical computed tomography (CT) datasets, structure sets, prescription doses, beam arrangements, and calculation parameters. Plans were compared using dose-volume histogram (DVH) metrics for target coverage and organ-at-risk (OAR) sparing, as well as total monitor units (MU). Compared with Ref, RP1 and RP2 showed statistically significant reductions in several OAR metrics, including bladder mean dose, bladder V15 Gy, penile bulb dose, and sigmoid dose. Urethral maximum dose increased with both RapidPlan-guided approaches, while urethral mean dose was not significantly different. Target dose differences were most notable for PTV_3625, while boost target coverage for PTV_mb_4250 was generally maintained. Both RapidPlan-guided approaches also significantly reduced total MU compared with Ref, suggesting reduced plan modulation and complexity. Overall, RapidPlan guidance improved selected OAR dose metrics in Ethos IOE v2 adaptive prostate SBRT planning, but further refinement may be needed to better balance target coverage and OAR sparing.

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