ASHBY: Accelerated Super-Hypofractionated Breast Brachytherapy

Inclusion Criteria:

* Female
* New diagnosis of ductal carcinoma in situ (DCIS) and/or invasive breast carcinoma per histologic evaluation
* Age 45-79 at diagnosis
* Previous lumpectomy with surgical margins histologically free of invasive tumor and DCIS as determined by the pathologist.
* T stage of Tis, T1, or T2.
* T2 tumors must be ≤3 cm in maximum diameter
* If the tumor is human epidermal growth factor receptor 2 (HER2)-positive, the patient must receive HER2-directed therapy.
* For patients with invasive breast cancer, an axillary staging procedure must be performed (either sentinel node biopsy alone or axillary dissection \[with a minimum of 6 axillary nodes removed\]) and the axillary node\[s\] must be pathologically negative.
* Note: N0(i+) is not an exclusion criterion.
* Note: Patients meeting all of the following criteria are not required to undergo the axillary staging procedure:

  * ≥70 years of age
  * estrogen receptor, Her2 = human epidermal growth factor receptor 2, PR = progesterone receptor negative (ER+PR+HER2-)
  * G1-2
  * Tumor ≤2 cm in size
  * Agrees to comply with aromatase inhibitor recommendation
* Ability to understand and the willingness to sign a written informed consent document in English

Exclusion Criteria:

* Pregnant or breastfeeding
* Active collagen-vascular disease
* Paget's disease of the breast
* History of DCIS or invasive breast cancer prior to the current diagnosis
* Prior breast or thoracic radiation therapy (RT) for any condition
* Multicentric carcinoma (DCIS or invasive)
* Synchronous bilateral invasive or non-invasive breast cancer
* Surgical margins that cannot be microscopically assessed or that are positive
* Excision cavity that cannot be clearly delineated per the treating investigator
* Any of the dosimetric treatment criteria defined in Section 6.1 have not been met. Patients who become ineligible due to inability to meet dosimetric criteria should not receive treatment as - defined in this protocol and will come off the study. Any subsequent adjuvant radiation will be delivered at the discretion of the treating physician
* Medical, psychological, or social condition that, in the opinion of the investigator, may increase the patient's risk or limit the patient's adherence with study requirements