Quality assurance of radiation therapy after breast-conserving surgery among patients in the BOOG 2013-08 trial

•In the BOOG 2013-08 trial, RT-protocol adherence was 98.5%.•Patients in a subanalysis received a mean breast dose of ≥95% of the prescribed dose.•The majority of patients received limited incidental RT dose on the nodal levels.•Incidental RT dose was comparable between treatment arms.•The lymph node volumes were never unintentionally treated with a V95%≥95%.