Date Approved

7-30-2026

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

School of Interdisciplinary Health

First Advisor

Alyssa Capizzi

Second Advisor

Jared Scroggins

Third Advisor

Kristen Vu

Fourth Advisor

Yue Yan

Fifth Advisor

Daniel Alexander

Academic Year

2025/2026

Abstract

Purpose: Craniospinal irradiation (CSI) is essential for treating pediatric and adult central nervous system malignancies, yet it exposes large volumes of normal tissue to low‑dose radiation, contributing to significant long‑term toxicity. This study evaluated whether incorporating anterior‑avoidance sectors (AVD) into volumetric modulated arc therapy (VMAT) planning would improve normal tissue sparing while maintaining target coverage and plan quality.

Materials and Methods: 8 previously treated CSI patients were retrospectively replanned using two VMAT techniques: Full Arc and AVD. All patients were simulated supine with standardized immobilization and planned in Eclipse. Identical target volumes, optimization structures, and planning objectives were used for both techniques. Dosimetric endpoints included PTV coverage (V95%), conformity index (CI), homogeneity index (HI), hotspot magnitude (D0.035cc), organ-at-risk (OAR), mean doses, low‑dose bath volumes and integral dose ratios. Statistical comparisons were performed using paired t‑tests.

Results: Target coverage, conformity, homogeneity, and hotspot magnitude were similar between Full Arc and AVD plans, with no statistically significant differences across PTV metrics (p = 0.430–0.818). AVD plans produced significant reductions in mean dose to multiple anterior abdominal organs, including bowel space, heart, liver, pancreas, spleen, and stomach (all p < 0.01 except stomach p = 0.003)—without increasing dose to thoracic structures. Normalized normal tissue integral dose was significantly and consistently lower with AVD for all patients (p < 0.001). Dose‑wash images demonstrated visibly reduced low‑dose spread with AVD.

Conclusion: AVD‑VMAT substantially reduces normal tissue doses while preserving target coverage and plan quality. Given the long‑term toxicity risks associated with CSI, particularly in pediatric patients, AVD represents a promising and clinically relevant planning strategy warranting broader adoption and prospective validation.

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