Inclusion Criteria:

- Female gender

- Age ≥18 years

- An invasive primary breast cancer of any histology arising from breast parenchyma

- Patient must be status post mastectomy or partial mastectomy with an assessment of
axillary nodes via sentinel lymph node biopsy and/or axillary lymph node dissection

- Pathologic confirmation of metastatic disease in at least one regional lymph node.
Regional lymph nodes are defined as the ipsilateral axillary lymph nodes, ipsilateral
supraclavicular lymph nodes, and ipsilateral internal mammary lymph nodes. Thus, any
T stage is allowed as long as the N stage is ≥1 and M stage is 0.

- Patient signed study-specific consent form.

Exclusion Criteria:

- Patients with distant metastasis.

- Patients who are pregnant or breastfeeding.

- Patients with psychiatric or addictive disorders that would preclude obtaining
informed consent.

- Time between initial diagnosis of breast cancer and start of radiation therapy
exceeds 13 months.

- Estimated life expectancy judged to be less than one year by patient's treating
radiation oncologist.

- Prior radiation therapy to the ipsilateral or contralateral breast or thorax.

- Primary breast cancer is a lymphoma or sarcoma histology.

- Patients with a history of non-skin malignancy <5 years prior to the diagnosis of
breast cancer.

- Patients requiring radiation to the bilateral breasts.