Date Approved

7-31-2023

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Allied Health Sciences

First Advisor

Kristen Vu

Second Advisor

Jessica Fountain

Academic Year

2022/2023

Abstract

Abstract

Introduction

Patients with a large breast volume are more at risk of adverse skin effects with radiation therapy. Studies concerning these patients are very limited, especially in regard to comparison of planning techniques. While traditional tangent 3D conformal radiation therapy has been the standard of care, recent literature has shown possible benefits of hybrid planning for average breast volume patients. Little has been studied regarding breast cancer patients with large breast volumes and the possible benefits of hybrid planning of this patient demographic. Creating a hybrid plan could have the benefits of both different treatment modalities to provide a better overall outcome for these types of patients.

Methods

This study was a plan comparison study of 10 hypofractionated breast cancer patients. A list of patients with a breast volume greater than 1300cc and a separation greater than 24cm was compiled. From this list of patients, those that received a hypofractionated treatment were selected. The retrospective nature means that all patients were already previously treated with a 16-fraction plan. The previously treated plan was copied and a partial arc was added starting at the angle of the medial tangent and ending at the angle of the lateral tangent. This beam set was given a low dose per fraction of 30%. The plans were compared on the basis of predetermined metrics to evaluate overall plan quality.

Results

Statistical analysis was performed on the quantitative data that was collected. The analysis was run by the GVSU statistics center using IBM SPSS Statistics. The paired T-Test was used to compare the 3D CRT plan to the hybrid treatment plan to find out if there is a dosimetric difference between the two planning techniques. Means, standard deviations, and p values were recorded. Results were given from metrics and objectives regarding the PTV, and OARs.

Conclusion

A hybrid 3D CRT and VMAT approach, when compared to a standard conventional 3D CRT tangent technique, may allow for the best of both techniques to be utilized. The results showed that while PTV coverage stays the same, the amount of 105% prescription dose, as well as the max dose, are decreased in the hybrid plan. There is significantly less prescription dose located outside of the PTV in the hybrid plan which, based on other studies, can decrease the toxicity to the skin. There were no significant differences regarding the ipsilateral lung constraint, the heart constraint, and the contralateral breast dose constraint. There was a difference in regards to the contralateral lung as the amount of 5Gy was higher for the hybrid plan. While there may be a trade off when looking at different planning techniques, it should be noted that a hybrid plan can be a more superior technique to 3D CRT in regards to patients with a larger breast volume.

Download

Included in

Oncology Commons

Share

COinS