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

Master of Science in Biomedical Sciences (MSBS), University of Toledo, 2015, Biomedical Sciences (Radiation Oncology)

The treatment regimen for breast cancer patients typically involves Whole Breast Irradiation (WBI). The coverage and extent of the radiation treatment is dictated by location of tumor mass, breast tissue distribution, involvement of lymph nodes, and other factors. The current standard treatment approach used at our institution is a 3D tangential beam geometry, which involves two fields irradiating the breast, or a four field beam arrangement covering the whole breast and involved nodes, while decreasing the dose to organs as risk (OARs) such as the lung and heart. The coverage of these targets can be difficult to achieve in patients with unfavorable thoracic geometries, especially in those cases in which the planning target volume (PTV) is extended to the chest wall. It is a well-known fact that exposure of the heart to ionizing radiation has been proved to increase the subsequent rate of ischemic heart disease. In these cases, inverse planned treatments have become a proven alternative to the 3D approach. The goal of this research project is to evaluate the factors that affect our current techniques as well as to adapt the development of inverse modulated techniques for our clinic, in which breast cancer patients are one of the largest populations treated. For this purpose, a dosimetric comparison along with the evaluation of immobilization devices was necessary. Radiation treatment plans were designed and dosimetrically compared for 5 patients in both, supine and prone positions. For 8 patients, VMAT and IMRT plans were created and evaluated in the supine position. Skin flash incorporation for inverse modulated plans required measurement of the surface dose as well as an evaluation of breast volume changes during a treatment course. It was found that prone 3D conformal plans as well as the VMAT and IMRT plans are generally superior in sparing OARs to supine plans with comparable PTV coverage. Prone setup leads to larger shifts in breast volume as well as in pos (open full item for complete abstract)

Committee: E. Parsai PhD (Advisor); D. Shvydka PhD (Committee Member); K. Reddy MD, PhD (Committee Member) Subjects: Medicine; Oncology; Physics; Radiation