Inclusion Criteria, if receiving postoperative radiation therapy

• Radiation oncologist recommends radiation treatment to the supraclavicular and infraclavicular fossa (i.e. RNI).
  
• Pathologically-confirmed invasive breast cancer. If patients undergo upfront surgery, the pathologic stage must be T0-T3, N0-N2a or N3a. If patients receive neoadjuvant chemotherapy prior to surgery, the clinical stage must be T0-T3, N0-N2a or N3a. T4b disease is permitted if the patient undergoes breast conserving surgery.
  
• Treatment with mastectomy or segmental mastectomy and axillary evaluation (sentinel node evaluation, axillary sampling, or axillary lymph node dissection). If the patient has T0 disease, breast surgery is not required.
  
• Age 18 years or older.
  
• If enrolling on in the arm lymphedema assessment cohort, documentation of arm volume measurement by perometer prior to axillary surgery.
  
• 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.
  
• Patients must be enrolled on the trial within 24 weeks of the later of two dates: the final breast cancer surgical procedure or administration of the last cycle of cytotoxic chemotherapy. If after trial enrollment it is determined the patient requires additional cytotoxic chemotherapy or additional breast cancer surgery prior to radiation therapy the patient may stay on trial but the patient must start radiation therapy within 24 weeks of the final breast cancer surgical procedure or administration of the last cycle of cytotoxic chemotherapy.

Inclusion Criteria, if receiving preoperative radiation therapy

• Surgeon and radiation oncologist recommend preoperative radiation therapy
•  Radiation oncologist recommends radiation treatment to the supraclavicular and infraclavicular fossa (i.e. RNI).
• Pathologically-confirmed invasive breast cancer. The clinical stage must be T0-T3, N0-N3b
•  Planned treatment with mastectomy and axillary evaluation (sentinel node evaluation, axillary sampling, or axillary lymph node dissection).
• Planned breast reconstruction with autologous reconstruction.
• Age 18 years or older.
• 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.

Exclusion Criteria, if receiving postoperative radiation therapy

• Pathologic or clinical evidence for a stage T4 breast cancer. However, T4b disease is permitted if the patient undergoes breast conserving surgery.
  
• Pathologic or clinical evidence for a stage N2b, N3b, or N3c breast cancer (supraclavicular, or internal mammary lymph node involvement).
  
• Clinical or pathologic evidence for distant metastases.
  
• Current diagnosis of invasive breast cancer in the contralateral breast (ductal carcinoma in situ is permitted).
  
• Prior diagnosis of invasive breast cancer in the contralateral breast.
  
• If enrolling on in the arm lymphedema assessment cohort, current diagnosis of bilateral breast cancer.
  
• History of therapeutic irradiation to the breast, lower neck, mediastinum or other area in which there could potentially be overlap with the affected breast. Except those patients enrolled and treated on the PRECISE trial (MD Anderson 2017-0362).
  
• Patient is pregnant.
  
• Patients who are cognitively impaired. Subjects will undergo a brief physical exam including a brief exam to determine cognitive review.
  

Exclusion Criteria, if receiving preoperative radiation therapy

• Pathologic or clinical evidence for a stage T4 breast cancer.
  
• Pathologic or clinical evidence for a stage N3c breast cancer (supraclavicular lymph node involvement).
  
• Clinical or pathologic evidence for distant metastases.
  
• Current diagnosis of invasive breast cancer in the contralateral breast (ductal carcinoma in situ is permitted).
  
• Prior diagnosis of invasive breast cancer in the contralateral breast.
  
• History of therapeutic irradiation to the breast, lower neck, mediastinum or other area in which there could potentially be overlap with the affected breast. Except those patients enrolled and treated on the PRECISE trial (MD Anderson 2017-0362).
  
• Patient is pregnant.
  
• Patients who are cognitively impaired. Subjects will undergo a brief physical exam including a brief exam to determine cognitive review.