Outcome of hypofractionated breast irradiation and intraoperative electron boost in early breast cancer: A randomized non‐inferiority clinical trial

Background Intraoperative electron radiotherapy (IOERT) followed by hypofractionated whole breast irradiation (HWBI) provides the shortest possible time of adjuvant breast irradiation. The efficacy of either method has been described in previous reports; however, to our knowledge, the efficacy of combined therapy has not been reported. Aim To compare the toxicity and cosmetic outcome of IOERT as a tumor bed boost followed by HWBI with conventional whole breast irradiation (CWBI) followed by external electron tumor bed boost (EETBB) after breast conserving surgery (BCS) in patients with invasive breast cancer. Methods In 2019, a prospective noninferiority trial (IRCT20180919041070N2) was started. After BCS, early‐stage breast cancer patients were treated by IOERT (10 Gy) and HWBI (42.56 Gy in 16 fractions) or CWBI (50 Gy in 25 fraction) and EETBB (10 Gy in 5) in a double‐arm design. Acute/late toxicity and cosmetic outcome were evaluated by common toxicity criteria (CTC) after 1‐year follow‐up (FUP) at the level of p