Overview

This non-inferiority, phase 3 clinical trial evaluates the cosmetic non-inferiority of a one-week regimen (26 Gy/5 Fx) versus a three-week regimen (40 Gy/15 Fx) using intensity-modulated radiation therapy (IMRT) for partial breast irradiation (PBI) in low-risk breast cancer patients post-breast-conserving surgery.

Eligibility

Inclusion Criteria:

• Female patients with an estimated life expectancy greater than 5 years. Meets criteria for either primary invasive breast cancer or pure ductal carcinoma in situ (DCIS).
• For invasive breast cancer: Age 40-75 years; Underwent breast-conserving surgery with sentinel lymph node biopsy or axillary lymph node dissection; pT ≤ 3 cm (unicentric/unifocal or total multifocal size ≤ 3 cm); favorable histology (invasive ductal, mucinous, tubular, or solid papillary carcinoma, DCIS component permitted); ER+ and/or PR+; pN0(i- or i+); M0; surgical margins ≥ 2 mm.
• For pure DCIS: Age 18-75 years; Underwent breast-conserving surgery with or without sentinel lymph node biopsy; low-to-intermediate nuclear grade; tumor size ≤ 2.5 cm; surgical margins ≥ 3 mm.
• Presence of surgical clips or distinct postoperative seroma/tissue changes in the tumor bed allowing precise target delineation.
• ECOG performance status 0 or 1.
• Eligible for systemic therapy, without prior neoadjuvant systemic therapy.
• Able to tolerate radiotherapy procedures and position immobilization.
• No contraindications to radiotherapy.
• Written informed consent provided.

Exclusion Criteria:

• Unfavorable histological subtypes (e.g., invasive lobular carcinoma, invasive micropapillary carcinoma).
• Positive axillary, internal mammary, or supraclavicular lymph nodes.
• Presence of distant metastasis.
• Paget's disease of the nipple.
• History of prior ipsilateral or contralateral invasive breast cancer or DCIS.
• Bilateral breast cancer.
• Known germline BRCA1 or BRCA2 mutation.
• Prior radiotherapy to the ipsilateral breast, chest wall, or regional lymph nodes.
• Active or prior second malignancy (except adequately treated non-melanoma skin cancer).
• Severe non-malignant comorbidities (e.g., cardiovascular disease, pulmonary disease, systemic lupus erythematosus, or scleroderma) precluding definitive radiotherapy.
• Pregnant or lactating patients.
• Inability or unwillingness to comply with scheduled follow-up visits.