Hypofractionated Regional Nodal Irradiation in Breast Cancer

Inclusion Criteria:

* Female
* Age ≥ 18 years old
* Life expectancy of \>5 years
* ECOG (Zubrod) performance status 0-1
* Histologically confirmed invasive carcinoma of the breast, including ductal, lobular, mammary, medullary, and tubular histologies
* Clinical T stage of cT0, cT1, cT2, or cT3
* Clinical N stage of cN0, cN1, or cN2a
* Clinical M stage of cM0Definitive surgery must be performed (either partial mastectomy or mastectomy without immediate reconstruction) with negative surgical margins (defined as no invasive tumor or DCIS on ink).
* Must have pathologic T stage of pT1, pT2, or pT3, or if receiving neoadjuvant chemotherapy, ypT0, ypTis, ypT1, ypT2, or ypT3
* Pathologic N stage of pN0, pN1, pN2a, or pN3a, or if receiving neoadjuvant chemotherapy, ypN0,ypN1, ypN2, or ypN3a) NOTE: any patient with clinically involved but undissected lymph nodes that would require a radiation boost will not be eligible.
* The radiation oncologist is planning to treat the breast/chest wall and ipsilateral regional lymphatics (including the axillary, supraclavicular, and internal mammary chains)
* Patient is able to understand and willing to sign an IRB approved written informed consent document
* All dosimetric constraints outlined in protocol section 3.5 can be met

Exclusion Criteria:

* Clinical or pathologic T4 disease, including inflammatory breast cancer
* Clinical N stage of cN2b, cN3 disease, pathologic N stage of pN2b, pN3b, or pN3c disease, or if receiving neoadjuvant chemotherapy, ypN2b, ypN3b, or ypN3c disease
* Radiologic evidence of gross residual disease
* History of prior ipsilateral breast cancer (invasive disease or DCIS)
* Active or history of another malignancy within 5 years of registration with the exception of basal cell or squamous cell carcinoma of the skin treated with local resection only or carcinoma in situ of the cervix
* Prior history of radiation therapy to the neck, breast, or thorax. Prior radioactive oral iodine is permitted.
* History of active collagen vascular disease including systemic lupus erythematosis, scleroderoma, or dermatomyositis with an elevated CK level
* Pregnancy, active breast feeding, or refusal or inability to use highly effective means of contraception in participants of child-bearing potential.
* The patient is a prisoner.