Inclusion Criteria:

1. Pathologically confirmed ductal carcinoma in situ of the breast or early invasive
breast cancer defined as pathologic stage Tis, T1, or T2, N0, N1mic, or N1a
(pathologic staging of the axilla is required for all patients with invasive disease
but is not required for patients with DCIS only).

2. Treatment with breast conserving surgery.

3. Final surgical margins must be negative, defined as no evidence for ductal carcinoma
in situ or invasive breast cancer touching the inked surgical margin. If the invasive
or in situ breast cancer approaches within less than 1 mm of the final surgical
margin, then a reexcision is strongly encouraged. Lobular carcinoma in situ at the
final surgical margin will be disregarded.

4. Age 40 years or older. This age cutoff is justified because breast cancers in women
under the age of 40 are known to have a significantly higher risk of IBTR presumably
due to underlying biologic differences.

5. Female sex.

6. Attending radiation oncologist declares intention to treat the whole breast only and
that a third radiation field to treat regional lymph nodes is not planned (radiation
of the undissected level I/II axilla with high tangents is allowed).

7. If the patient has a history of a prior non-breast cancer, all treatment for this
cancer must have been completed prior to study registration and the patient must have
no evidence of disease for this prior non-breast cancer.

8. Patients must be enrolled on the trial within 12 weeks of the later of two dates: the
final breast conserving surgical procedure or administration of the last cycle of
cytotoxic chemotherapy.

Exclusion Criteria:

1. Pathologic or clinical evidence for a stage T3 or T4 breast cancer.

2. Pathologic evidence for involvement of 4 or more axillary lymph nodes, or imaging
evidence of involvement of infraclavicular, supraclavicular, or internal mammary
lymph nodes.

3. Clinical or pathologic evidence for distant metastases.

4. Any prior diagnosis of invasive or ductal carcinoma in situ breast cancer in either
breast.

5. Current diagnosis of bilateral breast cancer.

6. History of therapeutic irradiation to the breast, lower neck, mediastinum or other
area in which there could potentially be overlap with the affected breast.

7. Patients not fluent in English or Spanish. (The Informed Consent will be available in
these two languages)

8. Patient is pregnant.