Master of Science in Biomedical Sciences (MSBS), University of Toledo, 2020, Biomedical Sciences (Medical Physics: Radiation Oncology)

Breast cancer patients are often treated in the prone position to improve dose homogeneity and cosmetic outcome. This is especially common when the patient's anatomy is more pendulous. A breast board is used to support the patient on the treatment table. This breast board creates a source of setup error as well as a source of error in the dose calculations of the treatment planning system. This study looks at two different methods for characterizing the board in the treatment planning system, compares the robustness of two different treatment planning methods across seven patients, and investigates the scatter contribution from the breast board. The first characterizing method was the material override method where a bulk density was assigned to the board shell and interior. The second characterizing method was the ROI type external method where the native CT numbers calculated during the simulation were used. A vertical transmission factor profile of the breast board was produced using each method and compared to the profiles obtained from an experimental setup. Seven previously anonymized patients were retrospectively selected, and two plans were made for each patient using the control point method and the augmented wedge method. The control point method is also known as “field-in-field”. This is when hot spots are covered with MLCs and the relative weights of the fields are changed to remove the hot spot. The augmented wedge method was when wedges and control points were used in the same plan. Planning with wedges alone was found to not be feasible. The plans had to have matching prescription coverage of 95%, as well as similar dose statistics. The robustness was compared by calculating the change in dose to a point in the dose shadow of the board when the board was completely removed, as well as the change in hotspot dose when the isocenter was slightly perturbed. The scatter contribution was investigated by measuring the skin dose of a virtual breast pha (open full item for complete abstract)

Committee: David Pearson (Committee Chair); E Parsai (Committee Member); Nicholas Sperling (Committee Member) Subjects: Physics; Radiation