Ultra-hypofractionated for Whole Breast Irradiation (WBI) Compared to Partial Breast Irradiation (PBI)

Ultra-hypofractionated for Whole Breast Irradiation (WBI) Compared to Partial Breast Irradiation (PBI): A Single-Institution Prospective Phase 2 Trial

Female patients undergoing surgical treatment for early breast cancer and meeting the inclusion criteria for adjuvant breast radiotherapy were randomized into two groups. One group will receive adjuvant whole-breast radiotherapy in ultra-hypofractionated regimen of 26 Gy in 5 fractions. In contrast, the other group will receive partial breast irradiation with a dose of 26Gy in 5 fractions.

The study's objective is to compare the effects of both breast radiotherapy protocols in terms of locoregional disease control and survival and to compare the adverse effects of radiotherapy between the two protocols. To determine if there is a correlation between different parameters and the efficacy and degree of toxicity for both protocols.

Radiation therapy should ideally start 6-8 weeks after breast-conserving surgery but no later than 12 weeks after the surgery.

If adjuvant chemotherapy has been administered, it is recommended to start radiation therapy three weeks after chemotherapy (optionally, it can be completed before beginning chemotherapy).

The radiation therapy procedure follows the existing clinical protocol for breast radiotherapy. For radiation therapy planning, the patient is positioned supine using immobilization devices (such as a wing board or similar) to ensure daily reproducibility within a range of 5 mm. The clinical target volume (CTV) is delineated according to the recommendations of the Danish Breast Cancer Cooperative Group (DBCG) and the European Society for Radiotherapy and Oncology (ESTRO).

A total dose of 26Gy in 5 fractions every working day using the Volumetric Modulated Arc Therapy (VMAT) technique. Daily portal images are obtained, and a breathing control protocol is applied based on clinical assessment (for left breast radiation therapy, active breath control is used - in deep inspiration or respiratory gating).

Inclusion Criteria:

• Breast-conserving surgery
• Invasive ductal carcinoma
• Age ≥ 50
• Tumor size ≤ 3 cm
• R0 resection
• Unicentric/unifocal carcinoma or multifocal carcinoma within 2 cm of the primary neoplasm
• pN0 (sentinel lymph node biopsy or axillary lymph node dissection performed), N1mi
• Hormone receptor status - any
• Histological grade G1 or G2

Exclusion Criteria:

• Neoadjuvant systemic therapy
• TNBC (triple-negative breast cancer)
• Extensive intraductal component (EIC)
• Lymphovascular invasion (LVI)
• associated DCIS > 2.5 cm in size or high nuclear grade