Date Approved

8-4-2025

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Allied Health Sciences

First Advisor

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

Second Advisor

Addah Riebschleger, M.S., CMD,

Academic Year

2024/2025

Abstract

This study aimed to evaluate whether a single-beam or two-beam configuration in GRID therapy offers superior tumor coverage to the Gross target volume(GTV) and organ-at-risk (OAR) sparing in head and neck cancer patients. Ten patients previously treated with GRID therapy to the left neck were retrospectively selected. For each patient, single-beam and two-beam plans were generated using consistent field size and energy. Dosimetric comparisons were performed using dose-volume histograms (DVHs), focusing on the highest dose received at any single point( dmax) and the average radiation dose delivered across an entire volume (dmean), and the volume covered by the 70% and 80% of the prescription. The Wilcoxon Signed-Rank test was used due to non-normal data distribution. Both techniques achieved clinically acceptable tumor coverage, with the two-beam approach showing modest improvements in 70% and 80% isodose line coverage. The two-beam plans also demonstrated potential benefits in reducing maximum and mean doses to certain OARs—most notably the mandible and brachial plexus. While spinal cord doses were slightly lower in single-beam plans for dmax, differences did not reach statistical significance (p =0.1094). All effect sizes ranged from negligible to moderate. Two-beam GRID therapy demonstrated favorable trends in tumor dose conformity and OAR sparing but did not show statistically significant advantages over single-beam plans. These findings support further investigation with a larger patient cohort to validate potential clinical benefits of different beam configurations in spatially fractionated radiation therapy (SFRT).

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