The purpose of this study is to determine whether high dose of radiation therapy (RT) are effective over standard 6-week radiation treatment in patients with breast cancer

Hypo-fractionation (several large fractions as the only radiation treatment) for breast cancer irradiation was common in the forties and 50s and, while very successful in achieving tumor control, was found to leave significantly inferior cosmetic results due to severe fibrosis and telangiectasia compared to those obtained with multiple fraction regimens (38-40). These complications were due to the use of very large fields, with the inclusion of a large proportion of uninvolved skin and tissue surrounding the tumor.

Based on these assumptions, a few large fractions can be safely delivered to breast cancers provided that 1) the target volume is sufficiently small and 2) the radiation technique assures maximum sparing of the surrounding normal tissue. Conformal RT to the tumor bed of T1 breast cancers satisfies both requirements.

Inclusion Criteria:

• Post-menopausal women (at least 2 years without menstrual period):

hysterectomized patients need follicle-stimulating hormone (FSH) confirmation of post-menopausal status.

• Original tumor non-palpable (mammographically detected).
• Small primary tumor (pT1) breast cancer, excised with negative margins (defined as at least a 5 mm margin).
• N0 or sentinel node negative or N0 clinically if the tumor is <1 cm in size.
• Patient offered six weeks of post-segmental mastectomy conventional radiation therapy and declined.
• Prescribed antihormonal therapy as part of their management.

Exclusion Criteria:

• Previous radiation therapy to the ipsilateral breast.
• Presence of a proportion of ductal carcinoma in situ (DCIS) in the pathology specimen which is compatible with extensive intraductal component (EIC).
• Women incapable of providing their own consent. Mental status will be assessed by the Principal Investigator using the Radiation Therapy Oncology Group (RTOG) Mini-Mental Status Examination.
• Women with a diagnosis of multifocal breast cancer.