Date Approved

8-8-2023

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Health Professions

First Advisor

Alan Mayville

Academic Year

2022/2023

Abstract

Objective

This retrospective study aimed to investigate the impact of CT slice thickness and isotropic grid size on treatment planning parameters for stereotactic radiosurgery (SRS).

Introduction

Stereotactic radiosurgery (SRS) enables the precise delivery of high doses of radiation to treatment volumes while sparing nearby normal tissues. Accurate measurement of these doses relies on the sampling of dose distribution across the treated structure. To achieve optimal dose accuracy, it is recommended to plan SRS treatments using thin computed tomography (CT) slice thickness and a small isotropic calculation grid. The American Association of Physicists in Medicine (AAPM) recommends a simulation CT slice thickness of no more than 1.25 mm and a calculation grid size of 2 mm or finer. While previous studies have explored the effects of grid size on dose calculation for spine stereotactic body radiation therapy (SBRT), the influence of thinner treatment planning CT scans on dose accuracy remains understudied. This study aims to investigate the impact of thinner treatment planning CT scans on dose calculation accuracy in the context of SRS, aiming to provide valuable insights for optimizing SRS treatment planning and enhancing the precision of dose delivery.

Methods

Data from The Cancer Imaging Archive (TCIA), specifically the Glioma Image Segmentation for Radiotherapy dataset, was utilized. Six previously treated patients with various malignancies were included. CT image sets were retrospectively reconstructed using the Eclipse treatment planning system to create datasets with CT slice thicknesses of 1.25mm and 0.625mm in addition to the original 2.5mm. Various treatment planning parameters, including maximum and minimum dose to the planning target volume (PTV), conformality index, gradient index, and PTV volumes, were analyzed using statistical methods, including two-way repeated measures ANOVA.

Results

The results revealed that the combination of CT slice thickness and isotropic grid size had a significant interaction effect on the absolute dose maximum, indicating the importance of selecting appropriate parameters for optimizing dose delivery. Isotropic grid size had a more pronounced effect on conformality index, while both CT slice thickness and isotropic grid size individually had statistically significant effects on the gradient index. PTV volumes increased with decreasing CT slice thickness, highlighting the impact of higher-resolution imaging on target volume delineation.

Conclusion

The findings of this study demonstrate the significance of CT slice thickness in treatment planning for SRS. Optimizing imaging parameters, such as CT slice thickness and isotropic grid size, can lead to improved dose delivery and treatment plan quality. However, further research with larger patient cohorts is warranted to validate and expand upon these findings, considering potential confounding factors and additional parameters that may influence treatment outcomes in the context of stereotactic radiosurgery.

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