Date Approved

8-6-2024

Graduate Degree Type

Project

Degree Name

Medical Dosimetry (M.S.)

Degree Program

Health Professions

First Advisor

Mubin Shaikh

Academic Year

2023/2024

Abstract

Introduction: This study investigates the dosimetric differences between sequential boost (SeB) and simultaneous integrated boost (SIB) techniques in prone breast radiotherapy for patients with large breast volumes, utilizing a 3D-CRT planning technique. Prone positioning in radiotherapy has shown to be effective in reducing heart and lung doses, yet limited research exists to compare overall plan quality between SeB and SIB using this technique. This analysis aims to evaluate whether SIB provides better dosimetric coverage and reduced dose to organs at risk (OARs) compared to SeB in prone breast radiotherapy.

Methods: A retrospective analysis was conducted on data from ten patients with breast volumes exceeding 1500cc, treated in a Midwest radiation oncology center. Three treatment plans were generated for each patient: a whole breast initial treatment followed by a SeB to the tumor bed, and a SIB plan. The metrics that were assessed included target coverage of the breast (V95>95) and tumor bed (V100>95), conformality, dose to OARs (heart mean dose), and several other metrics to assess high doses in the breast and tumor bed. Statistical analysis was performed using univariate tests to determine the significance of differences between these plans.

Results: SEQ plans showed better breast PTV coverage (98.59% vs. 97.8%, t=5.47, p=0.0004) and boost PTV coverage (99.27% vs. 95.93%, t=2.77, p=0.0214). Additionally, the mean heart dose was significantly lower in SEQ plans (55.9 cGy vs. 79.3 cGy, M=-5, p=0.002). Conversely, SIB plans demonstrated superior conformality index (0.49 vs. 0.31, t=-7.84, p<0.0001), with a large effect size of 2.57 (Cohen’s D). SIB plans also had significantly lower volumes of 105% and 107% doses in the breast (105%: 41.75% vs. 51.86%, t=6.04, p=0.0002; 107%: 30.22% vs. 36.03%, t=2.86, p=0.0187) and less boost prescription dose outside the boost PTV (6.62% vs. 14.47%, M=5, p=0.002). While SEQ plans excelled in target coverage and minimizing heart exposure, SIB plans offered advantages in dose distribution and conformality.

Conclusion: This study indicates that SIB can improve conformality and dose distribution. However, SeB plans were shown to provide better target coverage to both the breast and boost volume, as well as lower mean heart doses. The findings highlight the need for further research to optimize SIB planning techniques, particularly to utilize different beam angles to minimize cardiac exposure or more advanced 3D planning techniques. Considering the limitations of this study, additional research could include a larger and more diverse sample group to truly assess its potential for improved prone breast radiotherapy treatment.

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