| Breast cancer is the most common cancer in women and the second highest cause of cancer related deaths among women in the United States. A woman has a 1-in-8 lifetime risk of developing breast cancer and a 1-in-35 lifetime risk of dying from the disease. Most breast cancers are treated by some form of surgical intervention. Mastectomies remove the entire breast and were the gold standard for breast cancer surgery for almost 100 years. Eventually, surgeons began to gradually remove less and less breast tissue while achieving the same survival rates. Today, many women are eligible for breast conservation therapy, which is meant to preserve breast shape and structure by removing only the tumor and a small margin of surrounding non-cancerous tissue (known as a lumpectomy). An immense amount of evidence shows that there is no difference in overall survival rates between lumpectomy and the much more radical option of mastectomy, provided that complete tumor removal is achieved. A successful lumpectomy, therefore, includes negative margins (meaning that there are no cancer cells at the edges of the excised tissue) and an acceptable cosmetic outcome. Unfortunately, women eligible for breast conservation therapy may elect for a mastectomy due to surgical uncertainties. This is well founded considering a majority of studies report that positive margins occur in 16.5--40% of patients undergoing lumpectomy, resulting in an unacceptable rate of second surgeries and mastectomies. Surgical difficulties arise due to the inability to visualize the tumor in the operating room. Images of the tumor taken before surgery are acquired with the patient lying prone or standing up, while surgery is performed with the patient lying on her back. There can be drastic shape and location changes of the tumor between these two anatomical positions. A recent study published in the New England Journal of Medicine captures this backdrop well referring to breast cancer re-excision rates as " The Other Breast Cancer Epidemic". Reoperations cause patient pain, depression, anxiety, poor cosmetic outcomes, and an overall decrease in quality of life. Furthermore, reoperations are estimated to cost $53.7 million a year in surgical costs alone (Appendix A). This does not include hospital operational costs or outpatient costs.;This thesis addresses the need for improved surgical tools to localize tumors intraoperatively with the ultimate goal of reducing the number of reoperations associated with lumpectomy surgeries. The localization approach developed herein utilizes volumetric images of the breast taken prior to surgery and digitization technology to map patient images to the surgical space. Patient-specific tissue properties and biomechanical models are incorporated to correct the deformation that occurs between the breast geometry acquired by preoperative imaging and the breast geometry observed in the surgical setup. Once the preoperative images are corrected and co-registered to the patient in the operating room, surgeons can effectively navigate to tumors by using the co-registered preoperative images as patient-specific maps. The development of this image-guidance system for breast cancer surgery is detailed within this thesis, with chapters focusing on relevant background material, important research methods, initial assessment of tools and methods needed for an image guidance system, registration approaches, validation frameworks, the creation and integration of patient specific models, and a look into future studies to be performed. |
