Date Approved

7-29-2025

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Health Professions

First Advisor

Bethany Marshall

Second Advisor

Kristen Vu

Academic Year

2024/2025

Abstract

Abstract

Purpose: This study explored how the contralateral esophagus (CE) moves during a course of radiation therapy and how often it overlaps with the planning target volume (PTV) in patients with lung cancer. As far as it is known, no prior research has specifically measured how the CE behaves across treatment sessions.

Methods: A retrospective review was conducted on 10 patients out of an original 210 who met the inclusion criteria of esophageal overlap with the PTV. All patients received 60 Gy in 30 fractions using VMAT. For each patient, one CT simulation scan and seven cone-beam CT (CBCT) scans taken throughout treatment were analyzed. Key regions of interest included the measured esophagus (ME), speculated contralateral esophagus (SCE), and the portion of the esophagus within the PTV (MEWP). Rigid registration and manual contouring were performed, followed by binomial proportion exact testing and confidence intervals to evaluate volume changes over time.

Results: Significant variability was observed across all three measured regions. Five patients showed consistent reductions in ME volume, while only one met the desired criteria for SCE and MEWP across all time points. The largest observed volume increases were 211.24% (ME), 292% (SCE), and 217% (MEWP); the greatest decreases were 41.8%, 71.5%, and 35.0%, respectively. Confidence intervals were wide, reflecting variability among subjects.

Conclusions: These findings suggest that CE movement and volume changes occur throughout treatment, indicating that adaptive radiation therapy or periodic re-simulation may help improve accuracy and reduce toxicity, especially when the esophagus overlaps with the PTV. Further studies with larger cohorts are warranted.

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