Master of Science (MS)
Physics and Astronomy
Purpose: To determine if bolus electron conformal therapy (BECT) combined with volumetric modulated arc therapy (VMAT) and flattening filter free volumetric modulated arc therapy (FFFVMAT (6x and 10x)) can maintain equal or better dose coverage than standard volumetric modulated arc therapy (VMAT) while reducing doses to organs at risk (OARs). Methods: BECT+VMAT, FFFVMAT (6x and 10x), and VMAT treatment plans were produced for ten post-mastectomy radiotherapy (PMRT) patients previously treated at our clinic. The treatment plans were created on a commercially available treatment planning system (TPS) and all completed treatment plans were reviewed and approved by a radiation oncologist. The plans were evaluated based on planning target volume (PTV) coverage, tumor control probability (TCP), dose homogeneity index (DHI), conformity index (CI), dose to organs at risk (OARs), and second risks for OARs. Results: All techniques produced clinically acceptable PMRT plans. Overall, BECT+VMAT plans exhibited significantly higher maximum dose compared to all VMAT techniques. BECT+VMAT and FFFVMAT10x had slightly improved TCP over FFFVMAT6x and VMAT (p > 0.05). However, all VMAT techniques showed statistically significant improvement in CI and DHI over BECT+VMAT. All techniques showed no statistical significant difference in mean lung dose. BECT+VMAT exhibited a reduced mean heart dose over VMAT (p = 0.06). FFFVMAT6x had significantly higher mean heart dose compared to VMAT. In addition, BECT+VMAT was able to reduce mean dose to the contralateral breast with statistical significance, compared to VMAT. Both FFFVMAT techniques had comparable but slightly reduced dose compared to VMAT with FFFVMAT6x showing statistical significance. Conclusion: This work has shown that BECT+VMAT produces clinically acceptable plans while reducing OARs doses. Both FFFVMAT techniques are comparable to VMAT with FFFVMAT6x having slight improvements. In addition, FFFVMAT techniques exhibited reduced treatment times over VMAT. Even though all VMAT techniques produce more homogenous and conformal dose distributions, BECT+VMAT is a viable option for treating post-mastectomy patients. This work has demonstrated that patients with increased risk of cardiovascular disease or radiation-induced cancer of the contralateral breast may benefit from BECT+VMAT. Also, patients with increased risk of radiation-induced cancer of the contralateral breast may benefit from FFFVMAT6x.
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Heins, David Elward, "Comparison of Advanced Radiotherapy Techniques for Post-Mastectomy Breast Cancer Patients" (2016). LSU Master's Theses. 1882.