The purpose of this study is to test whether a radiotherapy regimen of 8 GY x 3 days over 5 days (every other day) is as safe (well-tolerated) and effective as 6 Gy x 5 over five consecutive days

Despite the fact that less extensive experience than that of brachytherapy is available, PBI delivery through an external-beam has many advantages. First of all, it is likely to be more acceptable to the patient since it is non-invasive and it does not require a surgical procedure or anesthesia. Moreover, since it is delivered after surgery, the pathological analysis of the segmental mastectomy specimen is available to inform the selection of the best candidates. In addition, EB-PBI is likely to become more widely reproducible, since it does not rely on the experience and skills of the radiation oncologist performing the brachytherapy implant. Besides, once the technique is established, it can be widely applied at any facility provided with a linear accelerator, without the risk presented by some brachytherapy approaches that can not be completed because of the unfavorable interplay of patient's anatomy with the technical limitations of the applicator.

The women in this study will receive either 5 or 3 radiation fractions to the tumor bed. We have chosen to study T1 post menopausal women because in this subset: 1) the tumor is small enough to be treated by partial breast radiation 2) the odds of having multicentric disease are low, making it ethical to avoid whole breast irradiation, 3) the most benefit from reducing the radiation schedule from 5 to 3 could be expected.

All patients will receive either 8 Gy x 3 over 5 days, every other day or 6 Gy x 5 over 5 days, on five consecutive days

Inclusion Criteria:

• Post-menopausal women defined as either:

  1. at least 2 years without menstrual period
  2. patients older than 50 with serological evidence of post-menopausal status
  3. hysterectomized patients of any age with FSH confirmation of post- menopausal status

• pT1 breast cancer, excised with negative margins. Criteria for low risk-pTis:

  1. Screen-detected
  2. Low to intermediate nuclear grade
  3. < 2.5cm in size
  4. Resected with negative margins at >3mm)

• clinically N0 or pN0 or sentinel node negative breast cancer

Exclusion Criteria:

• previous radiation therapy to the ipsilateral breast
• presence of a proportion of DCIS in the core biopsy specimen which is compatible with extensive intraductal component (EIC)

Baseline data was collected and analyzed for all participants.

From the date that subjects signed the ICF until the 5 years follow up visit (EOS)

Clinical assessment