Could a single day of radiation replace weeks of treatment for breast cancer?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Female * New diagnosis of Ductal Carcinoma in Situ (DCIS) and/or invasive breast carcinoma per histologic evaluation * Age 40-85 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 (HER2)-positive, the patient is planning to receive or has already received 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 (ER)+, progesterone receptor (PR)+/-, HER2- * Grade 1-2 breast cancer * Tumor ≤2 cm in size Note: If patients meet all the following criteria, the decision to avoid sentinel lymph node biopsy can be at the discretion of the breast surgeon: * 50-69 years of age * Grade 1-2 breast cancer * Clinically negative axilla by ultrasound and/or magnetic resonance imaging (MRI) * ER+, PR+, HER2- * Tumor ≤2 cm in size * Agrees to comply with aromatase inhibitor recommendation * Ability to begin brachytherapy within 12 weeks following lumpectomy, re- excision of margins, or completion of chemotherapy * Ability to understand and the willingness to sign a written informed consent document Exclusion Criteria: * Pregnant or breastfeeding * Active collagen-vascular disease * Paget's disease of the breast * Any prior history of DCIS or invasive breast cancer prior to the current diagnosis * Any prior history of breast radiation therapy (RT) or thoracic 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 * Treatment with neoadjuvant chemotherapy * Excision cavity that cannot be clearly delineated or is not amenable to implant per the treating investigator * 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