Date Approved

7-8-2026

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Allied Health Sciences

First Advisor

Emilie Soisson

Second Advisor

Kristen Vu

Academic Year

2025/2026

Abstract

Purpose: Palliative radiotherapy is commonly used for the treatment of thoracic spine metastases; however, conventional beam arrangements can expose nearby organs at risk (OAR), including the heart, to unnecessary radiation dose. This study evaluated whether replacing a static anterior beam with a conformal anterior arc could reduce cardiac dose while maintaining adequate target coverage.

Methods: Fifteen thoracic spine treatment plans were retrospectively replanned using an experimental technique in which the static anterior beam from the original plans was replaced with a 3D anterior conformal arc. All other planning parameters, including beam geometry, wedges, and multi-leaf collimator margins (MLC), were kept the same between the control and experimental plans. Dosimetric metrics were pulled from dose volume histograms (DVH) and were compared between the control and experimental plans. Statistical tests were carried out using the sign test. Significance was set at P < 0.05. Effect sizes were also calculated to evaluate the magnitude of differences between planning techniques.

Results: The target coverage was similar between the techniques, while ensuring that at least 95% of the planning target volume (PTV) received 100% of the prescription dose. Significant reductions in heart doses were achieved with the experimental 3D arc technique, including mean heart dose (819.56 cGy vs 667.33 cGy, P < 0.0001), heart D0.03cc (3310.05 cGy vs 3060.29 cGy, P = 0.001), heart V20 (0.12 vs 0.04, P = 0.001), heart V25 (0.03 vs 0.02, P = 0.0001), and heart V5 (0.55 vs 0.53, P = 0.0352). The mean lung dose and low dose lung volume dose metrics were slightly higher in the experimental plans.

Conclusion: Replacing a static anterior beam with a 3D conformal arc maintained target coverage while significantly reducing several heart dose metrics. This technique may provide a simple planning modification to improve cardiac sparing in thoracic spine palliative radiotherapy.

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