Partial breast irradiation (PBI) is becoming a new paradigm for breast cancer radiation.[1] No type I or II evidence is currently available to demonstrate equivalence to standard whole breast radiotherapy, and a prospective randomized trial jointly sponsored by NSABP and RTOG (NSABP B-39 and RTOG 0413) is currently accruing patients, comparing whole breast radiotherapy to PBI, either by brachytherapy or external beam techniques (EB). Until the results of this or similar trials are available, PBI remains a research domain, and it should be offered to patients only in the context of a clinical experimental protocol.

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. Finally, in terms of health care economics, an external beam approach spares the costs of an extra surgical procedure and that of several days of hospitalization (in the case of LDR brachytherapy).

Inclusion Criteria:

• Post-menopausal women defined as either:

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

• pT1 breast cancer, excised with negative margins

• pN0 or sentinel node negative or N0 clinically if the tumor is < 1 cm in size

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)