Evaluating the Safety and Efficacy of a Novel Accelerated Partial Breast Irradiation Regimen

Inclusion Criteria:

• Ability to provide informed written consent.

• Eastern Cooperative Oncology Group (ECOG) performance status of ≤ 3 or a Karnofskyperformance score of ≥ 30%.

• Willingness to return to Sanford Cancer Center for follow-up.

• Radiation therapy is planned as part of routine care.

• On histological examination, the tumor must be either ductal carcinoma in-situ (DCIS) or an invasive ductal carcinoma of the breast.

• Patients must be ≥ 50 years old.

• Presence of unifocal tumor.

• Surgical treatment of the breast must have been a lumpectomy. Placement of surgicalclips to delineate the lumpectomy bed is highly recommended, though not required.

• The final margins of the resected specimen must be histologically free of tumor (≥ 2mm for invasive adenocarcinoma and ≥ 3 mm for DCIS). Re-excision of surgical marginsis permitted. Gross disease must be unifocal with a pathologic invasive tumor sizetumor size ≤ 2.0 cm or pathologic DCIS size ≤ 2.5 cm.

• Patients with invasive breast cancer are required to have axillary stagingconsisting of a sentinel lymph node biopsy. The sentinel lymph node(s) must benegative for regionally metastatic disease, both on routine H&E evaluation andimmunohistochemical staining. Axillary staging is not required for patients withDCIS.

• Absence of lymphovascular space invasion.

• The tumor must be positive for either the presence of the estrogen or progesteronereceptor, and either 0 or +1 for the HER-2/neu receptor on immunohistochemicalstaining.

• The target lumpectomy cavity must be clearly delineated and the target lumpectomycavity to the whole breast reference volume ratio must be ≤ 30% based on theCT-simulation scan.

• Life expectancy of 5 years or longer excluding breast cancer diagnosis(co-morbidconditions taken into considerations by the PI)

• Women of child-bearing potential must have a negative pregnancy test before their CTsimulation, and must agree to use an effective method of birth control during theirradiation therapy treatment course.

Exclusion Criteria:

• Pregnant women, or women of childbearing potential who are unwilling to employadequate contraception.

• Nuclear grade 3 DCIS or Nottingham grade 3 invasive ductal carcinoma.

• Invasive lobular carcinoma, any grade.

• Male sex.

• Any treatment with radiation therapy, and/or hormonal therapy administered for thecurrently diagnosed breast cancer prior to study enrollment

• Prior breast or thoracic radiation treatment for any reason.

• History of prior invasive breast cancer or DCIS. (Patients with a history of LCIStreated by surgery alone are eligible.)

• Paget's disease of the nipple.

• Palpable or radiographically suspicious ipsilateral or contralateral axillary,supraclavicular, infraclavicular, or internal mammary nodes, unless there ishistologic confirmation that these nodes are negative for tumor.

• Patients with a collagen vascular disease; specifically, SLE or scleroderma.

• Breast implants. (Patients who have had implants removed are eligible.)

• Psychiatric or addictive disorders or other conditions that, in the opinion of theinvestigator, would preclude the patient from meeting the study requirements.

• Women with a known or suspected predisposition to developing breast cancer (i.e.,BRCA1/2 mutations, p53 mutation, etc...)

• Women who are pregnant, or women of child-bearing potential who refuse to use aneffective method of birth control