A phase II study investigating the acute toxicity of targeted intraoperative radiotherapy as tumor-bed boost plus whole breast irradiation after breast-conserving surgery in Korean patients

Background: There are concerns regarding local toxicity when IORT is applied in Asian women with a smaller breast volume than that of Western women. Trials are required to develop safety profiles for this technique. The aim of this trial was to evaluate acute toxicity after intra-operative radiotherapy (IORT) with low-energy X-ray plus whole breast irradiation (WBI) in Asian patients with breast cancer. Methods: This single-arm, single-institute, phase II trial investigated acute toxicity after completion of radiotherapy (targeted IORT followed by WBI) in Korean patients treated with breast-conserving surgery (BCS). In the conventional WBI arm from the TARGIT-A trial, the incidence of acute toxicity within 6 months was 15%. To prove the non-inferiority of the acute toxicity rate, 215 patients were required. This trial is registered with ClinicalTrials.gov (NCT02213991). Results: Two-hundred and fifteen women were enrolled, and 198 underwent IORT. In 33 patients, clinically significant complications during the acute period were noted. The incidence of acute toxicity was 16.7% (95% CI 11.5–21.9%). There were 29 patients with seroma needing more than 3 aspirations, 4 with wound infection, and 2 with skin breakdown. There was no difference in the rate of complications according to the tumor volume or the tumor-breast volume ratio. Advanced age and high BMI were risk factors for acute complications. Conclusions: Targeted intra-operative radiotherapy using Intrabeam® is a safe procedure for Korean patients with breast cancer with an acceptable toxicity profile in the acute period.