Standard or Hypofractionated Radiotherapy Versus Accelerated Partial Breast Irradiation (APBI) for Breast Cancer

Following breast conservative surgery, patients will be stratified according to the following prognostic factors using a minimisation technique: age (\<70 vs ≥70), HER2 status (HER2+ vs HER2-), hormonal receptor status (RH+ vs RH-) and lymph node invasion (pN0 vs pN0i+). Patients will be allocated to receive either standard treatment, hypofractionated treatment or APBI. Radiation therapy should be started between 4 and 12 weeks after the last surgery. Patients treated with standard whole breast irradiation will receive a total dose of 50 Gy in 25 fractions, 2 Gy per day, 5 days a week. The boost of 16 Gy will be delivered in 8 fractions for all patients after completion of the 50 Gy, without interruption. All patients will receive one fraction per day, 5 fractions a week. Patients treated with hypofractionated irradiation will receive a total dose of either 40 Gy (in 15 fractions, 2.66 Gy per day) or 42.5 Gy (in 16 fractions, 2.65 Gy per day) 5 days a week. Patients treated with APBI will receive a total dose of 40 Gy in 10 fractions, delivered twice a day over a time period of 5-7 days. Each daily dose must be separated by 6 hours. Patients will be followed at 3 and 6 month after the last dose of irradiation, at 12 months after the date of last surgery and then on a yearly basis during 10 years.