Single-Fraction Very Accelerated Partial Breast Irradiation (sfVAPBI)

To investigate clinical outcomes, late side effects, and cosmetic results of a single-fraction very accelerated partial breast irradiation as postoperative local treatment for the treatment of early stage breast cancer.

Inclusion Criteria: * Stage 0 \& I \& II (\< 3 cm) breast carcinoma * Lesions of \< 3 cm diameter * Invasive carcinoma of any subtype and grade or ductal carcinoma in situ (DCIS) * Nodal status: node-negative (pN0) or micro-metastatic (pN1mi) (patients with pN1mi status can be treated, but due to the limited clinical evidence, individual decision is needed) * M0: Absence of distant metastasis * Clear resection margins by National Surgical Adjuvant Breast and Bowel Project (NSABP) definition (no tumor on ink) * Unifocal (multifocality limited within 2 cm) and unicentric breast cancer * Age\> 40 years * Luminal A or B tumors * Time interval from surgery preferably less than 12 weeks and no longer than 20 weeks, and from adjuvant chemotherapy less than 4 weeks * Human Epidermal growth factor Receptor 2 positive (HER2+) patients receiving postoperative anti-HER2 systemic therapy * Specific signed consent form prior to randomization Exclusion Criteria: * Stage III-IV breast cancer * Surgical margins that cannot be microscopically assessed * Extensive intraductal component (EIC+) * Extensive lymphovascular invasion (LVI+) (focal is allowed) * Triple negative breast cancer * BReast CAncer gene (BRCA) 1-2 mutation * Human Epidermal growth factor Receptor 2 positive (HER2+) patients not receiving postoperative anti-HER2 systemic therapy * Neoadjuvant systemic therapy * Paget's disease or pathological skin involvement * Synchronous or previous breast cancer. * Pregnant or lactating women