This randomized Phase III study aims to show major complication rate of hypofractionation radiation therapy is not inferior, compared to conventional fractionation radiation therapy in breast cancer patients undergoing mastectomy and reconstruction surgery.

This study is a multicenter, randomized, phase 3 clinical trial. For breast cancer patients who underwent breast reconstruction after mastectomy, the hypofractionation radiotherapy group (experimental group) and the conventional fractionation radiotherapy group (control group) were divided 1:1 and compared to reveal the non-inferiority with hypofractionation in terms of major complication rate.

I. Primary Objective

• To show the non-inferiority of major complication rate in reconstructed-breast between the hypofractionation radiotherapy group (experimental group) and the conventional fractionation radiotherapy group (control group) at 2 years after radiation therapy.
• The main complications are defined at those requiring hospitalization or surgery among complications.

II. Secondary Objective:

• Comparison of other side effects between the two groups.

• Comparison of complication rate stratified by reconstruction timing and type of reconstruction

  • Immediate implant-based reconstruction
  • Immediate autologous reconstruction
  • Delayed-immediate implant reconstruction (2-stage)

• Comparison of quality of life between the two groups.

• Comparison of local and regional control rates between the two groups.

III. Tertiary Objective:

• Comparison of cosmetic evaluations between the two groups.
• Dosimetry analysis for correlation between the occurrence of complications and the dose profile.

Inclusion Criteria:

• Female patient who underwent mastectomy for invasive breast cancer
• Patients who have undergone breast reconstruction after mastectomy or who have inserted a tissue expander
• (y)p patients with stage IIIA or lower (excluding T4 and N3 patients) who need adjuvant radiation therapy
• Eastern Cooperative Oncology Group Performance ≤ 2
• Age ≥ 19 years
• Patients who agreed to participate in the study

Exclusion Criteria:

• Patients who already had implants at the time of diagnosis of breast cancer or who have already undergone reconstructive surgery
• Patients who underwent reconstruction after partial resection or breast conserving surgery rather than mastectomy
• Patients who are using or planning to use an air expander
• Patients receiving radiation therapy for salvage or palliative purposes
• Patients with distant metastases at the time of diagnosis
• Patients who are scheduled to undergo concurrent chemoradiation therapy
• Patients with bilateral breast cancer
• Male breast cancer patients
• Patients who have previously received radiation therapy for the ipsilateral breast or supraclavicular area
• Patients with history of cancers other than thyroid cancer, intraepithelial cancer of the cervix, or skin cancer
• Patients diagnosed with ductal breast carcinoma in situ, lobular carcinoma in situ, phyllodes, metaplastic cancer, or other benign tumors based on histological diagnosis