Inclusion Criteria:

   1. Diagnosed with clinical or pathologic stage I-III invasive breast cancer with TX-T3
   tumor

   2. Has been treated with mastectomy

   3. Has undergone immediate reconstructive surgery with placement of a tissue expander or
   permanent implant at time of mastectomy

   4. Is a candidate for unilateral post-mastectomy radiation therapy as per National
   Comprehensive Cancer Network (NCCN) guidelines (post-mastectomy radiation therapy is
   indicated for most patients with positive lymph nodes at time of surgery and
   infrequently for selected node-negative patients)

   5. Use of bolus is permitted, but not required

   6. Age ≥18

Exclusion Criteria:

   1. T4 cancer

   2. Recurrent breast cancer or history of prior breast radiation therapy

   3. Uncontrolled intercurrent illness including, but not limited to, ongoing or active
   infection, symptomatic congestive heart failure, unstable angina pectoris, and/or
   mental health illness that the consenting investigator feels would affect patient's
   ability to participate in this study

   4. Pregnant or nursing

   5. History of a different malignancy except for the following circumstances:

      - Disease-free for at least five years and deemed by the investigator to be at low
      risk for recurrence of that malignancy (<5 %).

      - Cervical cancer in situ and basal cell or squamous cell carcinoma of the skin

   6. Breast cancer requiring bilateral breast/chest wall radiation therapy.