Can breast radiation be cut from three weeks to one?

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

Inclusion Criteria: * Female patients with an estimated life expectancy greater than 5 years. * Meets criteria for either primary invasive breast cancer or pure ductal carcinoma in situ (DCIS). * For invasive breast cancer: Age 40-75 years; Underwent breast-conserving surgery with sentinel lymph node biopsy or axillary lymph node dissection; pT ≤ 3 cm (unicentric/unifocal or total multifocal size ≤ 3 cm); favorable histology (invasive ductal, mucinous, tubular, or solid papillary carcinoma, DCIS component permitted); ER+ and/or PR+; pN0(i- or i+); M0; surgical margins ≥ 2 mm. * For pure DCIS: Age 18-75 years; Underwent breast-conserving surgery with or without sentinel lymph node biopsy; low-to-intermediate nuclear grade; tumor size ≤ 2.5 cm; surgical margins ≥ 3 mm. * Presence of surgical clips or distinct postoperative seroma/tissue changes in the tumor bed allowing precise target delineation. * ECOG performance status 0 or 1. * Eligible for systemic therapy, without prior neoadjuvant systemic therapy. * Able to tolerate radiotherapy procedures and position immobilization. * No contraindications to radiotherapy. * Written informed consent provided. Exclusion Criteria: * Unfavorable histological subtypes (e.g., invasive lobular carcinoma, invasive micropapillary carcinoma). * Positive axillary, internal mammary, or supraclavicular lymph nodes. * Presence of distant metastasis. * Paget's disease of the nipple. * History of prior ipsilateral or contralateral invasive breast cancer or DCIS. * Bilateral breast cancer. * Known germline BRCA1 or BRCA2 mutation. * Prior radiotherapy to the ipsilateral breast, chest wall, or regional lymph nodes. * Active or prior second malignancy (except adequately treated non-melanoma skin cancer). * Severe non-malignant comorbidities (e.g., cardiovascular disease, pulmonary disease, systemic lupus erythematosus, or scleroderma) precluding definitive radiotherapy. * Pregnant or lactating patients. * Inability or unwillingness to comply with scheduled follow-up visits. Inability or unwillingness to provide written informed consent.