Date Approved

8-12-2026

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

School of Interdisciplinary Health

First Advisor

Addah Riebschleger

Second Advisor

Kristen Vu

Third Advisor

Raj Mitra

Academic Year

2025/2026

Abstract

Purpose: This phantom study looked at whether changing the Hounsfield unit (HU) value for radiopaque scar wires in Eclipse changed the calculated electron dose distribution. Methods and Materials: Radiopaque wires were placed in the same abdominal area on an anthropomorphic phantom. The wires were set up in a circle. The CT images were brought into Eclipse, the wires were contoured, and the planning target volume was made 1 cm inside the circle of wire. For every wire size and electron energy, two matching plans were made: one plan with no density override and one plan with a density override applied to the wire contour. The dataset contained 40 observations across 4 wire sizes (0.3 mm, 0.8 mm, 1.2 mm, and 2.0 mm), 5 electron energies (6, 9, 12, 16, and 20 MeV), and 2 planning conditions. The DVH metrics were Min Dose, Mean Dose, and D95. All dose values were reported as a percentage of the prescription dose. Results: Density override and Min Dose are two different things. Density override is the planning condition. Min Dose is one DVH dose metric. When density override was applied to the 0.3-mm wire, the Min Dose decreased in a statistically significant way. The average Min Dose was 67.42% with no override and 56.20% with an override. This was a mean difference of -11.22 percentage points (t=130.4, P< .001). No statistically significant override effect was found for the 0.8-mm, 1.2-mm, or 2.0-mm wires for Min Dose, Mean Dose, or D95. Conclusion: Applying an HU override to the wire contour changed the calculated Min Dose only for the 0.3-mm wire. It did not meaningfully change the larger target coverage metrics, including Mean Dose and D95. These results support using caution with HU overrides and making decisions based on the specific wire size rather than automatically overriding every radiopaque scar wire.

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