Inclusion Criteria:

- Histologically confirmed invasive breast cancer

- pT 1-2 (< 3 cm in diameter) pN0-N1 M0 according to TNM classification.

- Unifocal disease (confirmed radiologically and histologically)

- Eligible histotypes: all except for non-epithelial histotypes (lymphoma, sarcoma)

- Hormonal receptor status: indifferent

- Patients undergoing conservative breast surgery for neoplasms with a diameter < 3 cm
and with biopsy of the sentinel lymph node or first instance axillary dissection.

- Breast resection margins histologically negative (³ 2 mm) at first intervention or
after subsequent widening

- Radiological examination of the surgical specimen to assess the excision of the
hidden lesions and/or the microcalcifications if present in the mammography carried
out before surgery

- Positioning of 3-6 metallic clips, or in any case of an appropriate number to
delineate the area of surgical exeresis (tumor bed)

- At least two weeks must have elapsed from the end of the chemotherapy if this is
administered before the radiotherapy. In patients who do not receive chemotherapy,
radiotherapy should start < 12 weeks after surgery.

- No chemotherapy must be carried out during or at least two weeks after completion of
the radiotherapy

- Treatment with tamoxifen or aromatase inhibitors is allowed at the same time

- Age ³ 49

- Gender: female

- Menopause status: unspecified

- Performance status: 0-2 according to ECOG

- Life expectation: at least five years

- INFORMED consent: yes

- Non-hormonal contraception in patients of childbearing age

Exclusion Criteria:

- In situ carcinoma (CLIS and DCIS )

- Non-epithelial breast neoplasms (sarcoma, lymphoma etc.)

- Micro/macrometastases in > 3 axillary lymph nodes; micro/macrometastases in the
internal mammary and/or supraclavicular or subclavicular lymph nodes

- Multicentric carcinomas (lesions in different quadrants of the breast or in the same
quadrant but separated by at least 4 cm) or clinically or radiologically suspected
lesions in the ipsilateral breast, unless their tumoral nature was excluded through
biopsy or fine needle sample.

- Palpable radiologically suspected ipsilateral or contralateral axillary,
supraclavicular or infraclavicular, internal mammary nodes ( unless their tumoral
nature was excluded through biopsy or fine needle sample)

- Treatments for previous contralateral or ipsilateral breast cancers

- Paget's disease of the nipple

- Cutaneous involvement, independently of the tumor diameter

- Distant metastases

- Previous radiotherapy on the thoracic region

- Previous neoadjuvant chemotherapy

- Collagen diseases (systemic erythematosus lupus, scleroderma, dermatomiositis)

- Other pathological conditions that limit life expectancy to < 5 years

- Psychiatric diseases or disorders of other nature that prevent signing of informed
consent for the treatment

- Other neoplasms in the last 5 years with the exception of skin tumors apart from
melanoma and squamous intraepithelial lesions (SIL) of the uterine cervix

- Pregnancy and breast-feeding