Clinical Research Directory

Inclusion Criteria: * Female patients ≥ 51 years * Ipsilateral breast cancer; recurrence or second primary * Either histologically proven invasive adenocarcinoma (invasive adenocarcinoma with DCIS component is also accepted) or DCIS alone (calcification associated on imaging) * Histologically proven estrogen receptor positive * HER2neu negative * In case of invasive adenocarcinoma: tumor size ≤ 3 cm. In case of DCIS alone: affected area ≤ 2.5 cm * Grade I or grade II (biopsy) * cN0M0 (No evidence of nodal or distant metastases on axillary ultrasound and, if indicated, positron emission tomography-computed tomography (PET-CT) scan) * Unifocal lesions on mammogram and MRI (small satellite lesions adjacent to the tumor are accepted as long as it is suitable for local excision) * Interval since completion of local treatment of primary tumor \> 12 months * Previous radiotherapy (whole breast or partial) of the ipsilateral breast * Repeat breast conserving surgery feasible * World Health Organization (WHO) performance ≤ 2 * Written informed consent * The patient is legally competent Exclusion Criteria: * ≥ grade 3 radiotherapy toxicity in the breast after treatment of the primary tumor * Previous boost radiotherapy is not allowed, UNLESS the protocol tumor lies outside of the original boost area * Distant metastases and/or synchronous contralateral invasive or in situ carcinoma * Invasive lobular carcinoma (ILC) or pleiomorphic lobular carcinoma in situ (LCIS) * ER negative subtype * Lymphovascular invasion in biopsy * Neoadjuvant systemic treatment for the protocol tumor (except for pre-surgery hormonal therapy ≤ 2 months) * (Planned) oncoplastic surgery with major tissue displacement * Participation in another clinical trial that interferes with the locoregional treatment of this protocol. * It is expected that dosimetric constraints cannot be met, such as lung/heart constraints. * Patients with proven BRCA-mutations