Date Approved

7-11-2025

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Health Professions

First Advisor

Lee Culp, M.S., CMD, RT(T)

Second Advisor

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

Third Advisor

Bethany Marshall, M.S., CMD, RT(T)

Academic Year

2024/2025

Abstract

Purpose

This study intended to retrospectively compare the dosimetric effects of dwell times used in ring and tandem high-dose radiation (HDR) procedures in cervical and endometrial cancer patients. Specifically, whether reusing dwell times from the initial treatment to subsequent treatments creates a clinically significant dosimetric impact on a subject's treatment course.

Methods

Ten samples were picked for this retrospective study. The plans used in the actual treatment of each sample were compared to a newly created treatment plan reusing the exact dwell times used in the initial treatment in subsequent treatments. For each sample, the doses for individual constraints were summed across all five fractions to calculate a total dose for eleven separate constraints for statistical analysis. This step was completed for each planning style (reused and manually adjusted dwell times). A matched pairwise and sample t-test were conducted to compare radiation doses between plans using reused and newly generated dwell times.

Results and conclusions

The comparative dosimetric analysis between reused and newly generated dwell time plans revealed no statistically significant differences across all eleven dose constraint measures, including organs at risk (OARs), target volumes, and reference points. While several constraints showed near-normal distribution and some approached showing a statistical significance, all comparisons yielded small effect sizes, indicating minimal clinical impact. The results of this study suggest that reusing dwell times could offer a clinically comparable treatment plan to those with newly generated dwell times. This information could increase efficiency during treatment planning, without compromising treatment accuracy or patient safety. Due to the small effect size, future studies should use a larger sample size to understand further the clinical impact of dwell times on OARs and targets in ring and tandem radiation treatments.

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