A Phase I Dose-escalation Trial of Definitive Single Dose Stereotactic Body Radiotherapy in Low-risk Breast Cancer Patients: DESERT I Trial

Inclusion Criteria: * Over 18 years of age * Female gender * ECOG score 0-2 * Positive biopsy for invasive non-lobular breast tumor histology * Tumor \< 3 cm in diameter as measured by MRI or contrast mammography * Tumor located ≥ 0.5 cm from the skin or rib cage, clinically or radiologically * Positive estrogen and/or progesterone receptors * HER2 negative * No lymphovascular invasion in the biopsy * Tumor must be clinically and radiologically N0 (no lymph node involvement). If a suspicious lymph node is seen, it must be biopsied and show a negative result * Patient weight below 220 kg (weight limit for the treatment table) * Ability to tolerate the supine position for 20 minutes during treatment * Able to undergo MRI and/or contrast mammography * Not pregnant; women of childbearing potential will undergo a pregnancy test to rule this out * Contraindication to or refusal of surgical treatment, which must be explicitly documented in the medical record. Exclusion Criteria: * Under 18 years of age * Male gender * ECOG score 3-4 * Positive biopsy for invasive lobular carcinoma or ductal carcinoma in situ * Tumor ≥ 3 cm in diameter as measured by MRI * Tumor located \< 0.5 cm from the skin or rib cage, clinically or radiologically * Negative estrogen and progesterone receptors * HER2 positive * Presence of lymphovascular invasion in the biopsy * Positive BRCA mutation * Multicentric tumor * Tumor with positive axillary lymph nodes * Patients with metastatic disease * History of previous breast cancer in the same breast * Previous thoracic radiotherapy * Pregnant or actively breastfeeding * Unable to undergo MRI or contrast mammography * Unable to tolerate the supine position * Patient with breast implants * Patients with pacemakers * Scleroderma, lupus, or other connective tissue diseases with active flares * Inability to understand and sign the informed consent